DOI: 10.1148/rg.276065170
RadioGraphics 2007;27:1613-1634
© RSNA, 2007
Cross-sectional Imaging of Extranodal Involvement in Abdominopelvic Lymphoproliferative Malignancies1
Nuno Pinto Leite, MD,
Norbert Kased, BS,
Robert F. Hanna, BS,
Michele A. Brown, MD,
Jose M. Pereira, MD,
Rui Cunha, MD, and
Claude B. Sirlin, MD
1 From the Department of Radiology, Division of Body Imaging, University of California–San Diego, 200 W Arbor Dr, San Diego, CA 92103 (N.P.L., N.K., R.F.H., M.A.B., C.B.S.); and Department of Radiology, Hospital São João, Oporto Medical School, Miramar, Arcozelo, Portugal (N.P.L., J.M.P., R.C.). Presented as an education exhibit at the 2004 RSNA Annual Meeting. Received September 18, 2006; revision requested October 4 and received February 21, 2007; accepted May 10. C.B.S. received research funding from Bayer and from GE Healthcare; all remaining authors have no financial relationships to disclose.
Address correspondence to C.B.S. (e-mail: csirlin{at}ucsd.edu).
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Abstract
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Extranodal lymphoproliferative diseases are common, and their prevalence is increasing. Non-Hodgkin lymphomas and Hodgkin disease, in particular, frequently involve extranodal structures in the abdomen and pelvis, including both the solid organs (liver, spleen, kidneys, and pancreas) and the hollow organs of the gastrointestinal tract. Because virtually any abdominopelvic tissue may be involved, many different imaging manifestations are possible, and lymphoproliferative diseases may mimic other disorders. Familiarity with the imaging manifestations that are diagnostically specific for extranodal lymphoproliferative diseases is important because imaging plays an important role in the noninvasive management of disease. However, a definitive diagnosis requires a biopsy (of bone marrow, a lymph node, or a mass), a peripheral blood analysis, and other laboratory tests. In patients with known disease, the goals of imaging are staging, evaluation of response to therapy, and identification of new or recurrent disease or of complications of therapy. In patients without known disease, imaging permits a provisional diagnosis.
© RSNA, 2007
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Outline appropriate imaging strategies for the diagnosis of extranodal lymphoproliferative diseases in the abdomen and pelvis.
- Recognize key abdominopelvic imaging features that allow differentiation of extranodal lymphoproliferative diseases.
- Describe the implications of imaging findings for disease management.
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Introduction
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Lymphoproliferative disorders are a subgroup of hematologic malignancies that comprises four different malignancy types: non-Hodgkin lymphomas, Hodgkin disease, lymphocytic leukemias (acute or chronic), and plasma cell myeloma (multiple myeloma). The first two types, non-Hodgkin lymphomas and Hodgkin disease, frequently involve nodal and extranodal structures in the abdomen and pelvis; these disorders are the subject of this article (Table 1). Lymphocytic leukemias and multiple myeloma, apart from the possible occurrence of enlarged lymph nodes and bone lesions, are typically associated with normal abdominopelvic findings and thus are not discussed here.
The article reviews pathologic and imaging manifestations of extranodal lymphoproliferative diseases in the abdomen and pelvis, with emphasis on involvement of the solid abdominal organs (liver, spleen, kidneys, and pancreas) and hollow organs of the gastrointestinal tract (stomach, small bowel, and colon). Correlative imaging strategies with computed tomography (CT), magnetic resonance (MR) imaging, and ultrasonography (US) are described, and characteristic findings and diagnostic pitfalls are discussed in detail.
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Basic Concepts
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Non-Hodgkin Lymphomas and Hodgkin Disease
The group of non-Hodgkin lymphomas comprises more than 30 subtypes of lymphoma that have clinical and pathologic features distinct from those of Hodgkin disease. At imaging, non-Hodgkin lymphomas and Hodgkin disease show considerably different patterns of nodal involvement (Table 2).
Extranodal Lymphoma
The term extranodal lymphoma refers to non-Hodgkin lymphoma or Hodgkin disease in sites other than the lymph nodes, spleen, thymus, tonsils, and pharyngeal lymphatic ring (Waldeyer throat ring) (1,2). The classification of disease as nodal or extranodal is identical for Hodgkin disease and non-Hodgkin lymphomas except in cases of splenic involvement: In Hodgkin disease, splenic involvement is considered nodal, whereas in non-Hodgkin lymphomas it is considered extranodal (3). Nevertheless, splenic Hodgkin disease is described in this article to complete the discussion of solid organ involvement.
In general, extranodal involvement is more common in non-Hodgkin lymphomas than in Hodgkin disease (20%–40% vs 4%–5% of cases) (1,2,4) and more common in patients with recurrent disease (5) or immunodeficiency-related disease (5–9) than in patients with an initial manifestation. In addition, because of the increased use of immunosuppressive therapy and the more prolonged survival of patients with a deficient immune status (including those with acquired immunodeficiency syndrome [AIDS]), the prevalence of immunodeficiency-related lymphoma has increased. Although the introduction of highly active antiretroviral therapy in 1995 led to a dramatic reduction in the incidence of some AIDS-related malignancies (eg, Kaposi sarcoma and primary central nervous system non-Hodgkin lymphoma), the incidence of systemic non-Hodgkin lymphoma has remained stable. Consequently, non-Hodgkin lymphoma is now the most common AIDS-related cancer (10).
Posttransplantation lymphoproliferative disease is a serious and relatively common (2%–5%) complication of immunosuppressive therapy related to solid organ transplantation (11) and is particularly frequent after cyclosporine therapy (5,6). Imaging features of this disease are similar to those of AIDS-related non-Hodgkin lymphoma, with more than 80% of cases showing extranodal involvement. As many as one-half of these patients have disease confined to the abdomen (4,11,12).
Primary versus Secondary Lymphoma
Extranodal lymphoma is classified as primary if involvement is confined to a single organ and immediately adjacent lymph nodes (eg, lymph nodes in the organ hilum or in the surrounding fat). Extranodal lymphoma is classified as secondary if there is involvement of nodes other than those immediately adjacent to the primary organ or involvement of more than one extranodal site. In general, primary extranodal lymphoma is much less common than secondary extranodal lymphoma, usually by one or two orders of magnitude. Primary extranodal lymphoma is more common in patients with AIDS or immunodeficiency with another cause than in patients with normal immune systems, and it is more likely to be non-Hodgkin lymphoma than Hodgkin disease (10).
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Role of Imaging
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Although noninvasive imaging plays an important role in the management of lymphoid neoplasms, diagnosis requires biopsy (eg, bone marrow, lymph node, or mass), peripheral blood analysis, and other laboratory tests. In patients with known disease, the goals of imaging are staging, evaluation of response to therapy, and identification of new or recurrent disease or of complications of therapy. In patients without known disease, imaging permits a provisional diagnosis.
Currently, many imaging modalities are available for the assessment of lymphoid neoplasms. These modalities can be divided into three categories: anatomic, functional, and combined.
Anatomic Imaging
Anatomic imaging includes chest radiography, CT, lymphangiography, MR imaging, and US. CT is the preferred modality for anatomic imaging of non-Hodgkin lymphomas and Hodgkin disease because it permits assessment of lesion size, shape, and relation to adjacent structures. In addition, unlike other modalities (eg, radiography, lymphangiography, MR imaging, and US), CT allows anatomic imaging evaluation of almost all regions of the body (3,13). However, CT is limited in that as many as 20%–30% of patients with Hodgkin disease confined to supradiaphragmatic structures on the basis of CT have undetected infradiaphragmatic involvement, often of the spleen, at staging laparotomy (13,14).
Historically, lymphangiography has been considered the most reliable nonsurgical method for diagnosing diseases of the lymph nodes and lymphatic vessels. CT and positron emission tomography (PET)/CT have reduced the role of lymphangiography. However, unlike the newer modalities, lymphangiography has the theoretical advantage of being able to show internal architectural changes within normal-sized lymph nodes. This powerful capability makes lymphangiography more accurate than CT for some lymphomas (15,16).
Lymphangiography, however, does have some disadvantages. It is invasive and time consuming, requires technical expertise, and may cause patient discomfort and complications (17). In an attempt to overcome these limitations, contrast material–enhanced MR lymphangiography was developed. The MR imaging technique is performed with the concomitant administration of an intravenous or interstitial contrast agent to aid in visualization of the lymphatic system. Contrast agents being examined for this purpose include superparamagnetic iron oxide particles and some gadolinium chelates. The utility of MR lymphangiography is still under investigation (18).
MR imaging is more sensitive than CT for the detection of chest wall invasion, meningeal and spinal cord involvement, and bone marrow infiltration (3). It is necessary in patients with contra-indications to CT and for further characterizing nonspecific lesions detected at CT. In particular, MR imaging has higher accuracy for differentiating microabscesses from lymphoma nodules. However, MR imaging is less available than CT, is not as practical for full-body diagnostic imaging, and has limited accuracy for the detection of pulmonary parenchymal disease.
US is useful for characterizing focal lesions detected at CT as cystic or solid and for detecting renal obstruction in patients with acute renal failure. US does not play a routine role in lymphoma staging.
Functional Imaging
Functional imaging modalities available for the assessment of lymphoma include gallium 67 (67Ga) scintigraphy and 2-fluorine-18 (18F) fluorodeoxyglucose (FDG) PET. Regions in the body with increased levels of metabolic activity exhibit increased uptake of both FDG and 67Ga. PET and 67Ga scintigraphy take advantage of this property to enable better depiction of lymphoma. FDG PET has high sensitivity (88%–100%) for detection and staging of Hodgkin disease and non-Hodgkin lymphomas (2,13,19) and is rapidly replacing 67Ga scintigraphy as the functional imaging method of choice (20). Advantages of FDG PET over 67Ga scintigraphy are higher accuracy, better spatial resolution, same-day imaging, and a lower radiation dose (21). In addition, FDG PET has high diagnostic accuracy for differentiating recurrent or residual tumor from scar tissue and can help predict the response to therapy. If available, PET should be performed instead of 67Ga scintigraphy (20,21).
However, PET has disadvantages, which include its limited availability compared with that of anatomic imaging modalities such as CT (20) and the short half-life of the cyclotron-produced isotope. Also, certain normal tissues (eg, bone marrow) and tissues affected by benign conditions (eg, inflammation and infection) may show elevated FDG uptake, and low-grade lymphomas may have low FDG activity. Thus, overlap in the degree of FDG uptake between benign and malignant conditions may lead to diagnostic uncertainty (22). Moreover, the differential diagnosis for extranodal lymphoma may include fungal microabscesses, other opportunistic infections, and adenocarcinomas. PET often is not helpful for differentiating lymphoma from these other entities. Strategies to counteract these limitations include the following: obtaining baseline images before therapy, as references for posttreatment images; administering agents such as diazepam and furosemide to decrease the uptake of 18F FDG in nonmalignant lesions; and remaining attentive to the possibility of a condition mimicking lymphoma in an immunosuppressed patient (22).
Combined Anatomic and Functional Imaging
PET/CT is a recent technical advance that allows dual-modality imaging in a single session to obtain both anatomic and functional information. The acquisition of complementary PET and CT data in the same examination permits characterization of both the metabolic status and the structural appearance of lesions (2) and thus helps overcome the individual limitations of each modality. The capacity to use CT attenuation data to correct the emission data during PET image reconstruction is an important additional benefit of PET/CT compared with PET alone and allows a decrease of the total data acquisition time to 25 minutes or less per patient. After completion of the unenhanced PET/CT acquisition, contrast-enhanced CT may be performed; however, the latter is not necessary for lymphoma staging or restaging in most cases of Hodgkin disease and non-Hodgkin lymphomas (23). PET/CT images of extranodal lymphoma are available in the existing literature (2), and therefore none are included in the present article.
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Selection of the Imaging Strategy
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The selection of appropriate imaging modalities is complex and depends on the patient, the radiologist, and institutional constraints. If available, PET/CT, which offers higher accuracy and sensitivity than PET or CT alone for lymphoma detection, is the procedure of choice for initial staging and follow-up (23,24). If PET/CT is unavailable, a reasonable imaging strategy might include chest radiography and CT of the neck, abdomen, and pelvis; or CT of the neck, chest, abdomen, and pelvis might be performed, eliminating the need for chest radiography. The frequency of follow-up imaging examinations varies and is generally based on the stage and grade of disease, the initial site of involvement, and clinical evidence of recurrence. As described earlier, lymphangiography may be useful in selected patients.
In patients with extranodal abnormalities observed at PET/CT or at routine follow-up CT or PET, tailored examinations (eg, biopsy, multiphasic CT, or MR imaging) may be necessary to help characterize the abnormalities, narrow the differential diagnosis, and guide management (13). As technology evolves, the relative importance of different modalities undoubtedly will shift, but radiologists likely will continue to play an important role in helping determine the most appropriate imaging strategy for individual patients.
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Imaging Features of Extranodal Involvement
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The imaging characteristics of extranodal lymphomatous involvement are classified here according to the site of involvement in (a) the solid abdominal organs or (b) the hollow organs of the gastrointestinal tract.
Solid Organ Involvement
Involvement of the spleen, liver, kidneys, pancreas, adrenal glands, and testes in lymphoma is discussed in this section. Involvement of other organs, such as the uterus, ovaries, and prostate, is not discussed here because it is rare.
In general, lymphomatous involvement of the solid organs may occur as a focal, multifocal, or diffuse disease process. In focal and multifocal disease, discrete solid nodules are present; in diffuse disease, there is uniform infiltration of the involved site.
Unifocal (solitary) or multifocal (multiple) nodules are round, well-defined, and homogeneous. Enhancement after the administration of intravenous contrast material tends to be mild and uniform. However, central necrosis may occur and produce a heterogeneous appearance on unenhanced or contrast-enhanced images (25). Calcification is rare in the absence of treatment. Nodules may mimic metastases, primary cancer, infection, or granulomatous disease. Noninvasive differentiation of lymphoma from these other entities is important because the work-up, treatment, and prognosis may vary considerably.
On US images, nodules usually are homogeneously hypoechoic and may resemble cysts. The absence of posterior acoustic enhancement indicates that the lesions are solid and permits a correct diagnosis. Nodules may have a bull’s-eye appearance.
On CT scans, nodules commonly are hypoattenuating when compared with the surrounding organ parenchyma but have attenuation values higher than that of water. When multiple nodules are depicted at CT, an observation of similar attenuation in all the nodules (none of which have the attenuation of water) helps exclude a diagnosis of multiple complicated cysts. The observation of subtle enhancement or washout on images obtained during different enhancement phases after intravenous contrast material administration helps confirm that the nodules are solid.
At MR imaging, nodules tend to have low to intermediate signal intensity on T1-weighted images and moderately high signal intensity on T2-weighted images. However, the signal intensity of nodules is not as high as that of water on T2-weighted images. Moreover, images acquired with sequences that are highly fluid sensitive (eg, single-shot echo-train spin-echo or steady-state free precession sequences) may help reliably exclude a diagnosis of multiple cysts.
Compared with normal parenchyma, lymphoma nodules usually are hypovascular and enhance less after intravenous contrast material administration (3,25–27) (Figs 1, 2). A lesion that appears subtly enhanced on CT scans may be more obviously enhanced on MR images because of the greater sensitivity of MR to the contrast material.
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Figure 1. Diffuse hepatosplenic involvement in lymphoma. Axial CT scan obtained after the administration of oral and intravenous contrast media shows multiple round, homogeneous, hypoattenuating nodules (arrows) in both the liver and the spleen.
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Figure 2. Splenic involvement in non-Hodgkin lymphoma. Axial contrast-enhanced CT scan shows a large, hypoattenuating, heterogeneous round mass in the spleen (arrowhead). The mass appears less enhanced than the normal splenic parenchyma and has central areas of lower attenuation (arrow) that are suggestive of ischemia or necrosis.
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In contrast to the nodular form of disease, diffuse involvement of the solid organs may produce no structural abnormalities and tends to be difficult to detect with anatomic imaging. The most common finding is organomegaly, but this feature has very low sensitivity and specificity for the diagnosis of lymphoma. Organ contour usually is normal or only minimally abnormal, even if diffuse disease is advanced. Images obtained after the administration of an intravenous contrast material may depict subtle heterogeneous areas that are not visible on unenhanced images. FDG PET may be helpful for depicting lymphoma in organs such as the liver and spleen (13).
Lymphoma may infiltrate an organ from adjacent tissue. Alternatively, it may extend from an organ into tissue around that organ, as occurs commonly with lymphoma in the kidneys and pancreas. When lymphoma infiltrates tissues outside the organ, it tends to be amorphous and exerts a minimal mass effect for its size. These characteristics are suggestive of the diagnosis.
Spleen.—
Secondary involvement of the spleen is common in both non-Hodgkin lymphomas and Hodgkin disease (2). Primary splenic lymphoma is rare (28).
Diffuse, uniform infiltration is the most common form of splenic lymphoma. The imaging appearance of the affected spleen usually is normal, but ill-defined hypoenhancing foci with diameters of less than 1 cm may be apparent after intravenous contrast material administration. Splenomegaly may occur but is not diagnostically specific; even in the absence of splenic involvement, the spleen in a patient with lymphoma may enlarge because of a reactive process. However, findings of marked splenomegaly (3,26,27) and of splenomegaly in conjunction with splenic hilar adenopathy (27) are suggestive of splenic infiltration.
Discrete nodules (Fig 3) are present in a minority of patients with splenic lymphoma. Nodules may be missed on arterial phase and early venous phase images because of normal heterogeneous splenic enhancement. Late venous phase and equilibrium phase images allow a more reliable assessment of splenic involvement in lymphoma.
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Figure 3. Non-Hodgkin lymphoma involving the spleen. Axial CT scan obtained during equilibrium phase enhancement after the administration of oral and intravenous contrast media shows innumerable hypoattenuating lesions in the spleen (arrows).
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Patients affected by lymphoma may be immunocompromised and as a result may be vulnerable to disseminated fungal infections (eg, candidiasis and aspergillosis), which may appear as multiple nodules with diameters ranging from 2 to 20 mm in the spleen, liver, and other solid abdominal organs (29). The differentiation of multinodular splenic lymphoma (Figs 4, 5) from fungal microabscesses is critical but may be challenging. Fungal microabscesses typically are smaller than lymphoma nodules and characteristically occur in the absence of lymphadenopathy (Fig 6). In comparison with the homogeneous enhancement typical of lymphoma nodules (Fig 7), the contrast enhancement of fungal microabscesses tends to be more heterogeneous; common patterns include enhancement in the center of a nodule and peripheral rimlike enhancement. In addition, patients with fungal microabscesses usually are febrile and neutropenic (Table 3).
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Figure 4. Multinodular splenic lymphoma. Axial contrast-enhanced CT scan obtained during the venous phase shows heterogeneous splenic enhancement, with multiple faintly hypoattenuating lesions (arrowheads). Note the enlarged mesenteric and retroperitoneal lymph nodes, with encasement but not invasion of the surrounding vasculature (arrows).
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Figure 5. Hepatic, splenic, and lymph node involvement in non-Hodgkin lymphoma. Axial CT scan obtained after the administration of oral and intravenous contrast media shows relatively well-defined, hypoattenuating, hypoenhancing lesions in the liver (*) and spleen (arrows) and lymphadenomegaly around the aorta (arrowheads).
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Figure 6. Splenic microabscesses. Axial contrast-enhanced CT scan shows small hypoattenuating lesions throughout the spleen (arrows). The lesions are smaller than typical lymphoma nodules.
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Figure 7a. Non-Hodgkin lymphoma complicated by neutropenic colitis. (a) Axial CT scan obtained after the administration of oral and intravenous contrast media shows massive enlargement of the spleen, which has displaced the left kidney posteriorly, and a hypoattenuating focal mass in the anterior part of the spleen (arrow). (b) Axial contrast-enhanced CT scan obtained at a lower level than a shows mural thickening and stratification (arrowheads), features suggestive of submucosal edema, in the cecum.
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Figure 7b. Non-Hodgkin lymphoma complicated by neutropenic colitis. (a) Axial CT scan obtained after the administration of oral and intravenous contrast media shows massive enlargement of the spleen, which has displaced the left kidney posteriorly, and a hypoattenuating focal mass in the anterior part of the spleen (arrow). (b) Axial contrast-enhanced CT scan obtained at a lower level than a shows mural thickening and stratification (arrowheads), features suggestive of submucosal edema, in the cecum.
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Table 3. Frequency of Observation of Imaging and Clinical Features in Hepatic and Splenic Lymphoma Nodules and in Fungal Microabscesses
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No imaging technique consistently depicts hepatosplenic fungal infections, but MR imaging probably has the highest sensitivity for this purpose (30–32). The lesions generally have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images; however, the signal characteristics may change during the course of treatment (29). CT has lower sensitivity for the detection of small abscesses but is more readily available and therefore is more frequently used (25). Fungal microabscesses typically appear as round circumscribed lesions with low attenuation at CT. MR images may show the characteristic central or peripheral areas of enhancement with greater clarity than do CT scans.
Liver.—
Primary hepatic lymphoma is extremely rare and occurs most commonly in immunocompromised patients. Secondary involvement of the liver in advanced stages of lymphoma is relatively common. Both primary and secondary hepatic lymphomas are more often non-Hodgkin lymphoma than they are Hodgkin disease. At the time of presentation, the liver is involved in up to 15% of patients with non-Hodgkin lymphoma and in up to 10% of patients with Hodgkin disease (2,3,27). Hepatic Hodgkin disease almost always occurs in conjunction with splenic disease, and the more extensive the splenic disease, the greater the likelihood of hepatic involvement (27). In contrast, hepatic non-Hodgkin lymphoma may occur in the absence of splenic disease.
As secondary lymphoma is more common than primary lymphoma in the liver, lymph node disease is present in most patients with hepatic lymphoma. Typically, the paraaortic, celiac, mesenteric, and periportal nodes are involved. Histologically, liver parenchymal involvement in non-Hodgkin lymphoma or Hodgkin disease begins in the periportal tissue (27).
Diffuse infiltration is the most commonly occurring pattern of Hodgkin disease and non-Hodgkin lymphoma in the liver. This pattern is easily overlooked on cross-sectional images because the liver has a homogeneous appearance. Hepatomegaly may occur but is nonspecific for hepatic lymphoma.
Discrete nodules (Figs 8–10) occur in about 10% of cases of Hodgkin disease and non-Hodgkin lymphomas of the liver and may appear with a miliary pattern. Dominant liver masses are atypical in secondary lymphoma (3,25,26) but are characteristic of primary lymphoma. In contrast to the homogeneous nodules typical of secondary hepatic lymphoma, the dominant masses of primary hepatic lymphoma may be heterogeneous (Figs 8, 9) and may mimic primary or metastatic carcinoma of the liver.
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Figure 8. Primary non-Hodgkin lymphoma of the liver in a patient with a positive test result for human immunodeficiency virus (HIV). Sagittal US image of the liver shows a hypoechoic mass (demarcated by electronic calipers) that measures 60 x 49 mm and has smooth, regular margins. The higher echogenicity (*) at the center of the mass probably represents ischemia or necrosis.
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Figure 9a. Primary non-Hodgkin lymphoma of the liver in an HIV-positive patient (same patient as Fig 8). Axial CT scans obtained before the administration of contrast material (a), during arterial phase enhancement (b), and during delayed phase enhancement (c) show a hypoattenuating mass in the right hepatic lobe (black arrowhead in a), with an enlarged retrocaval node (* in a) and an incidental gallbladder stone (white arrowhead in a). The mass appears minimally enhanced after the administration of intravenous contrast material (b, c) and has a central region of hypoattenuation that likely represents ischemia or necrosis (white arrow in b). Note the transient change in attenuation of the parenchymal tissue around the mass during the arterial phase (black arrows in b). At image interpretation, a prospective diagnosis of carcinoma metastasis or primary liver carcinoma was considered. Subsequent biopsy results indicated lymphoma.
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Figure 9b. Primary non-Hodgkin lymphoma of the liver in an HIV-positive patient (same patient as Fig 8). Axial CT scans obtained before the administration of contrast material (a), during arterial phase enhancement (b), and during delayed phase enhancement (c) show a hypoattenuating mass in the right hepatic lobe (black arrowhead in a), with an enlarged retrocaval node (* in a) and an incidental gallbladder stone (white arrowhead in a). The mass appears minimally enhanced after the administration of intravenous contrast material (b, c) and has a central region of hypoattenuation that likely represents ischemia or necrosis (white arrow in b). Note the transient change in attenuation of the parenchymal tissue around the mass during the arterial phase (black arrows in b). At image interpretation, a prospective diagnosis of carcinoma metastasis or primary liver carcinoma was considered. Subsequent biopsy results indicated lymphoma.
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Figure 9c. Primary non-Hodgkin lymphoma of the liver in an HIV-positive patient (same patient as Fig 8). Axial CT scans obtained before the administration of contrast material (a), during arterial phase enhancement (b), and during delayed phase enhancement (c) show a hypoattenuating mass in the right hepatic lobe (black arrowhead in a), with an enlarged retrocaval node (* in a) and an incidental gallbladder stone (white arrowhead in a). The mass appears minimally enhanced after the administration of intravenous contrast material (b, c) and has a central region of hypoattenuation that likely represents ischemia or necrosis (white arrow in b). Note the transient change in attenuation of the parenchymal tissue around the mass during the arterial phase (black arrows in b). At image interpretation, a prospective diagnosis of carcinoma metastasis or primary liver carcinoma was considered. Subsequent biopsy results indicated lymphoma.
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Figure 10a. Primary non-Hodgkin lymphoma of the liver. Axial contrast-enhanced CT scans obtained during the portal venous phase (a) and the delayed phase (b) show a large, lobulated, hypoattenuating mass (arrows in a) that causes anterior protrusion of the liver border. Despite contrast material washout, there is no appreciable difference in the attenuation of the mass between the portal venous and delayed phases.
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Figure 10b. Primary non-Hodgkin lymphoma of the liver. Axial contrast-enhanced CT scans obtained during the portal venous phase (a) and the delayed phase (b) show a large, lobulated, hypoattenuating mass (arrows in a) that causes anterior protrusion of the liver border. Despite contrast material washout, there is no appreciable difference in the attenuation of the mass between the portal venous and delayed phases.
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Disseminated fungal microabscesses of the liver and spleen are an important diagnostic pitfall (Table 3) because they may mimic multifocal lymphomas (Fig 1). CT and US do not permit reliable differentiation on the basis of imaging findings alone. As mentioned earlier, MR imaging may be more helpful for differentiating between these two entities.
Differentiation of hepatic lymphomas from carcinoma metastases is usually more straightforward, as lymphoma nodules tend to be smaller and more homogeneous than carcinoma metastases and do not usually show the rimlike and targetlike enhancement patterns characteristic of carcinoma metastases.
Pancreas.—
The pancreas is involved secondarily in more than 30% of patients with non-Hodgkin lymphoma. Primary pancreatic lymphoma is uncommon (33); it accounts for less than 2% of extranodal non-Hodgkin lymphomas in immunocompetent hosts and 5% or less of cases in patients with AIDS (12,34–37). Pancreatic Hodgkin disease is extremely rare (3).
Diffuse pancreatic involvement causes organ enlargement as well as irregular peripancreatic fat infiltration, and it may resemble acute pancreatitis on imaging (38) (Fig 11). In comparison with the normal pancreas, an affected gland may have slightly lower attenuation on unenhanced CT scans, lower signal intensity on T1-weighted MR images, and higher signal intensity on T2-weighted MR images. Contrast enhancement is diffusely reduced, yet homogeneous (38,39). Although serum amylase levels may be elevated, patients do not have clinical signs of pancreatitis. Colon, lung, breast, and gastric cancers all may metastasize to pancreaticoduodenal nodes and mimic pancreatic or peripancreatic lymphoma.
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Figure 11a. Non-Hodgkin lymphoma of the pancreas. Axial contrast-enhanced CT scans (b at a lower level than a) show an amorphous hypoattenuating mass that involves the body and tail of the pancreas (arrowheads in a) but that has not invaded the vessels (arrows in b).
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Figure 11b. Non-Hodgkin lymphoma of the pancreas. Axial contrast-enhanced CT scans (b at a lower level than a) show an amorphous hypoattenuating mass that involves the body and tail of the pancreas (arrowheads in a) but that has not invaded the vessels (arrows in b).
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Unifocal pancreatic lymphoma manifests as a well-circumscribed mass. It may occur in any part of the gland. In the pancreatic head, it may cause mild dilatation of the duct of Wirsung and the common bile duct and may mimic pancreatic adenocarcinoma (Fig 12). Imaging features that help differentiate pancreatic lymphoma and adenocarcinoma are summarized in Table 4. In general, a bulky pancreatic head mass that causes relatively little pancreatic duct dilatation and little pancreatic tail atrophy is more characteristic of lymphoma than of adenocarcinoma. Both lymphoma and adenocarcinoma may be associated with peripancreatic lymph node enlargement; however, lymphadenopathy below the level of the renal veins is virtually never found in adenocarcinoma except at an advanced stage. Heterogeneous enhancement or calcification is suggestive of adenocarcinoma, whereas calcification in pancreatic lymphomas has not been reported. The envelopment of adjacent vessels without evidence of obstruction is suggestive of lymphoma (39) (Fig 13). Multifocal pancreatic lymphoma may occur but is uncommon (34); moreover, to our knowledge, it is not described in the radiology literature.
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Figure 12. Non-Hodgkin lymphoma of the pancreas. Axial CT scan obtained after the administration of intravenous contrast material shows a heterogeneously enlarged pancreatic head (white arrows) that encases the superior mesenteric vein and that is associated with enlarged retroperitoneal lymph nodes (black arrow). Heterogeneous enlargement of the spleen (*) and resultant posterior displacement of the left kidney also are depicted.
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Figure 13a. Adenocarcinoma of the pancreas. Curved planar reformatted images obtained with CT after the administration of oral and intravenous contrast media show a large hypoattenuating mass in the pancreatic head (* in a). The mass obstructs and causes dilatation of the pancreatic duct (arrows in a) and common bile duct (arrows in b).
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Figure 13b. Adenocarcinoma of the pancreas. Curved planar reformatted images obtained with CT after the administration of oral and intravenous contrast media show a large hypoattenuating mass in the pancreatic head (* in a). The mass obstructs and causes dilatation of the pancreatic duct (arrows in a) and common bile duct (arrows in b).
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Kidneys.—
Primary renal lymphoma is rare. Secondary renal lymphoma, which occurs mainly in late-stage disease, is more common; it is much more frequently non-Hodgkin lymphoma than Hodgkin disease, but the imaging features of the two entities are similar (40). About 7%–14% of patients with non-Hodgkin lymphomas develop renal lymphoma (41), usually by direct extension from contiguous retroperitoneal lymphoma or by hematogenous spread (5,40,42,43).
Diffuse infiltration occurs in approximately 20% of patients with renal lymphoma and is almost always bilateral (44). Lymphomatous proliferation begins in the renal interstitium and causes nephromegaly, usually with preservation of the renal contour (45). Renal enlargement may be the only imaging manifestation, although an infiltrating tumor may encase and deform the renal sinus (5,45) (Fig 14). Images obtained after the intravenous administration of contrast material may show poorly enhancing areas in the kidneys.
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Figure 14. Renal lymphoma. Axial contrast-enhanced CT image obtained during the late corticomedullary phase demonstrates stranding in the renal hilum and perirenal fat (arrows). There is a subtle increase in the heterogeneity of the kidney, with blurring of the renal cortex and renal pyramid interfaces. Note the renal enlargement with encasement and deformation of the renal sinus.
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The most frequent pattern of renal lymphoma (60% of cases) is multiple masses (5,41,43), usually in both kidneys (5) (Fig 15). The lesions are homogeneous and small (1–3 cm), and they enhance less markedly than does the normal renal parenchyma (41,43). Intralesional areas of heterogeneous low attenuation may occur after chemotherapy and are thought to represent tumor necrosis (41).
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Figure 15. Multifocal non-Hodgkin lymphoma involving both kidneys. Axial CT scan obtained during the nephrographic phase after the administration of oral and intravenous contrast media shows multiple hypoattenuating nodules throughout both kidneys (black arrows). Areas of soft-tissue attenuation in the perirenal fat (white arrows) likely represent perirenal infiltration by lymphoma.
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In about 10%–20% of patients with renal lymphoma, images depict a solitary renal mass that typically is homogeneous and hypovascular, with minimal enhancement. These features are not characteristic of renal cell carcinomas, which tend to be heterogeneous and enhance rapidly (40,43,44). The size of renal lymphoma masses varies from small to large, and large masses may distort the renal contour (44) (Figs 16, 17). Renal lymphomas also may invade the perirenal space or the renal hilum.
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Figure 16. Renal lymphoma. Axial CT scan obtained after the administration of oral and intravenous contrast media demonstrates a hypoattenuating well-defined mass (arrows) in the left kidney.
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Figure 17a. Renal lymphoma. Axial CT scans, obtained before the administration of oral and intravenous contrast media (a) and during corticomedullary (b), nephrographic (c), and 3-hour delayed (d) enhancement phases, show the right kidney. The delayed phase image also depicts a large hypoattenuating renal mass (arrows in d), a feature that is barely visible on the images from earlier phases because of attenuation or enhancement similar to that of the normal renal parenchyma. Multiple enlarged lymph nodes, some calcified, also are seen in the left paraaortic (arrow in a and c) and aortocaval (arrowheads in b) regions.
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Figure 17b. Renal lymphoma. Axial CT scans, obtained before the administration of oral and intravenous contrast media (a) and during corticomedullary (b), nephrographic (c), and 3-hour delayed (d) enhancement phases, show the right kidney. The delayed phase image also depicts a large hypoattenuating renal mass (arrows in d), a feature that is barely visible on the images from earlier phases because of attenuation or enhancement similar to that of the normal renal parenchyma. Multiple enlarged lymph nodes, some calcified, also are seen in the left paraaortic (arrow in a and c) and aortocaval (arrowheads in b) regions.
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Figure 17c. Renal lymphoma. Axial CT scans, obtained before the administration of oral and intravenous contrast media (a) and during corticomedullary (b), nephrographic (c), and 3-hour delayed (d) enhancement phases, show the right kidney. The delayed phase image also depicts a large hypoattenuating renal mass (arrows in d), a feature that is barely visible on the images from earlier phases because of attenuation or enhancement similar to that of the normal renal parenchyma. Multiple enlarged lymph nodes, some calcified, also are seen in the left paraaortic (arrow in a and c) and aortocaval (arrowheads in b) regions.
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Figure 17d. Renal lymphoma. Axial CT scans, obtained before the administration of oral and intravenous contrast media (a) and during corticomedullary (b), nephrographic (c), and 3-hour delayed (d) enhancement phases, show the right kidney. The delayed phase image also depicts a large hypoattenuating renal mass (arrows in d), a feature that is barely visible on the images from earlier phases because of attenuation or enhancement similar to that of the normal renal parenchyma. Multiple enlarged lymph nodes, some calcified, also are seen in the left paraaortic (arrow in a and c) and aortocaval (arrowheads in b) regions.
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The contiguous extension of a retroperitoneal mass into the kidney accounts for about 25% of cases of renal lymphoma. Lymphoma in such cases typically manifests as a homogeneous, bulky, retroperitoneal mass that cloaks but does not obstruct the renal vessels. It often invades the renal hilum and may cause hydronephrosis (41). The involved kidney occasionally is displaced (Fig 18).
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Figure 18. Non-Hodgkin lymphoma involving the right kidney. Axial contrast-enhanced CT scan shows a large, amorphous, predominantly hypoattenuating retroperitoneal mass (arrows) that has invaded the right kidney and distorts its contour. The mass also has encased but has not occluded the blood vessels. Note the enlarged lymph nodes in the left paraaortic region (*).
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Perirenal lymphoma manifests as an amorphous soft-tissue mass that surrounds but does not invade the kidney. Additional findings may include renal sinus infiltration and thickening of the Gerota fascia. Intravenous contrast material administration is important to allow differentiation between normally enhancing uninvolved renal parenchyma and mildly enhancing involved perirenal tissues (43) (Figs 19, 20). This pattern of enhancement is thought to result from the direct extension of retroperitoneal disease or of parenchymal disease through the renal capsule.
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Figure 19. Perirenal lymphoma. Unenhanced CT scan shows heterogeneous enlargement of both kidneys (*). The soft-tissue attenuation of the perirenal fat obscures the renal margins and is indicative of perirenal involvement. Bilateral renal vacuolar calcifications are incidentally depicted.
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Figure 20. Perirenal lymphoma. Axial contrast-enhanced CT scan shows a large perirenal soft-tissue mass (arrows) that displaces the left kidney laterally. The renal parenchyma appears normal, but small aortocaval nodes are visible.
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Findings that are atypical of renal lymphoma include spontaneous hemorrhage, necrosis, heterogeneous attenuation, cyst formation, and calcification (5). In cases where these features are present, biopsy usually is necessary to exclude renal cell carcinoma or metastases.
Adrenal Glands.—
Adrenal lymphoma is rare, and non-Hodgkin lymphoma is the most frequent subtype. According to published data, the adrenal gland is involved in 4% of patients with non-Hodgkin lymphoma (1,2). Involvement is bilateral in 50% of cases, and patients may present with adrenal insufficiency. Imaging findings are nonspecific. The most common finding is unilateral or bilateral diffuse enlargement of the adrenal gland (Figs 21, 22). In addition, retroperitoneal adenopathy or other extranodal lesions usually are identified.
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Figure 21. Adrenal gland lymphoma. Axial contrast-enhanced CT scan demonstrates a large homogeneous mass in the right adrenal gland (*). Note the normal size of the left adrenal gland (arrow) in contrast to that of the right gland.
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Figure 22. Adrenal gland lymphoma. Axial contrast-enhanced CT scan shows a hypoattenuating mass in the left adrenal gland (*) with extension to the left perirenal space (arrowheads). The mass abuts but has not invaded the kidney.
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Testes.—
Lymphoma accounts for only 5% of testicular tumors, but it is the most common testicular tumor in patients older than 60 years (2). Testicular involvement is more frequent in non-Hodgkin lymphoma, being virtually nonexistent in Hodgkin disease (1). Involvement is bilateral in up to 40% of cases (2). The testes may be the only site of disease, or, in cases of disease recurrence, may be one of multiple sites. Lymphoma usually involves the body of the testis and spares the tunica vaginalis. The epididymis and spermatic cord are frequently affected (1). The initial imaging modality of choice is US, but US findings are not diagnostically specific. The most common US features are well-defined hypoechoic areas within an enlarged testis (Fig 23).
Involvement of the Gastrointestinal Tract
Unlike adenocarcinoma, which arises from the mucosa, lymphoma may originate in and extend along the submucosa or the deep mucosal layer. Because of this pattern of extension, lymphomas may be missed at endoscopy. If a lymphomatous process is included in the differential diagnosis, the radiologist should alert the endoscopist, who then may closely evaluate the area of concern and perform a biopsy that extends deep to the mucosa (46).
CT is easy to perform and is accurate for the evaluation and staging of gastrointestinal lymphoma (46). It provides important pretherapeutic information about tumor location, morphology, and extension, as well as about the involvement of lymph nodes and other organs. CT staging has important therapeutic implications because stage I and II disease may be excised, whereas stage III and IV disease must be treated with radiation, chemotherapy, or both. In addition, CT allows accurate monitoring of the response to therapy.
Typical CT findings include mild to moderate circumferential thickening of the stomach or bowel wall. Luminal constriction, dilatation, or cavitation also may be observed. Lesions may be solitary or multiple and are usually homogeneous, although large lesions that include areas of internal hemorrhage or ischemia may appear heterogeneous. The tumor usually is hypoattenuating or isoattenuating in comparison with the normal bowel, and it enhances less than does the normal bowel after intravenous contrast material administration. Bulky, diffuse regional or mesenteric lymphadenopathy typically is present and helps differentiate lymphoma from other gastrointestinal lesions (27,47).
Lymphomatous involvement of the gastrointestinal tract may occur in the following morphologic forms: nodular, polypoid, infiltrative, aneurysmal or cavitary, ulcerative, and mixed. In the nodular form, there is nodular thickening of the involved segment, with a range of nodule sizes. In the polypoid form, which occurs most commonly in the stomach, solitary or multiple smooth polyp-like masses are present, and the surrounding tissue is normal or thickened.
In the infiltrative form, there is focal or diffuse thickening of the involved segment because of tumor extension along the submucosa and muscularis propria. Peristalsis may be impaired, and the involved segment may have a tubelike appearance. Rarely, there may be segmental luminal narrowing and obstruction. Diffuse infiltration may lead to destruction of the muscularis propria and autonomic plexus. The involved segment becomes nonperistaltic, circumferentially dilates, and assumes an aneurysmal appearance. The dilated segment usually has irregular, lobulated margins, which sometimes contain small nodules (48). The tumor may excavate the mesentery, producing a cavitated mass. In addition to lymphoma, the differential diagnosis in cases with the aforementioned features includes gastrointestinal stromal tumor (GIST), perforated colonic carcinoma (49,50), and metastatic disease (especially melanoma).
Infiltration by lymphoma also may lead to mural ulceration. When this occurs in the stomach, it produces an abnormal bulge in the gastric contour, that fills with oral contrast material; however, differentiation of this feature from a simple peptic ulcer or a superficial carcinoma may be difficult. In the small bowel, multiple ulcerative lesions typically are present, and fistulas and perforations may occur. As opposed to the aneurysmal or cavitary form, in which mural involvement tends to be circumferential, the ulcerative form usually affects the bowel wall asymmetrically and may be exophytic.
When a lengthy bowel segment is involved in lymphoma, alternating constriction and dilatation may occur (48). This pattern is referred to as a mixed form of involvement.
Stomach.—
The stomach is the portion of the gastrointestinal tract most frequently involved in lymphoma (approximately 50% of cases). Nevertheless, gastric lymphoma is much less common than gastric adenocarcinoma or GIST; lymphoma accounts for only 3%–5% of all malignant gastric neoplasms (51,52). Non-Hodgkin lymphoma is about ten times more common than Hodgkin disease among gastric lymphomas. In addition, secondary gastric lymphoma is more common than primary lymphoma (3,48). Gastric lymphoma has no site predilection, and all portions of the stomach are equally likely to be involved.
The most common primary gastric lymphoma is low-grade mucosa-associated lymphoid tissue (MALT) lymphoma (53), previously known as pseudolymphoma. This condition, which is responsible for 50%–70% of all primary gastric lymphomas, is associated with Helicobacter pylori infection and may regress completely after antibiotic therapy (54). MALT lymphoma also may progress to high-grade B-cell non-Hodgkin lymphoma, and it is now believed that most high-grade B-cell lymphomas arise from MALT lesions.
Of the patterns of gastrointestinal involvement noted above, those most commonly observed among gastric lymphomas are the infiltrative pattern with thickened folds, the polypoid pattern, the cavitary pattern, the nodular pattern, and the mixed pattern (52,55). Because the imaging features of MALT lesions overlap with those of high-grade lymphomas, differentiation is not possible on the basis of imaging alone, and a biopsy may be required.
Another important entity in the differential diagnosis is gastric adenocarcinoma (Table 5). The following characteristics favor a diagnosis of lymphoma: (a) diffuse, extensive, or severe gastric wall thickening; (b) minimal or mild tumor enhancement; (c) preservation of the perigastric fat plane; (d) distensibility of the gastric lumen; (e) bulky, smooth lymphadenopathy; and (f) lymphadenopathy below the renal pedicle, particularly if there is no associated perigastric lymphadenopathy (56) (Fig 24). The following findings favor a diagnosis of adenocarcinoma: (a) milder, more focal wall thickening; (b) relatively greater tumor enhancement; (c) direct tumor infiltration beyond the gastric wall (Figs 25, 26); and (d) gastric mural rigidity and luminal narrowing (linitis plastica), which may result in obstruction. Perigastric adenopathy is seen in 50%–60% of cases of both lymphoma and adenocarcinoma and therefore is unhelpful for differentiation when it is an isolated finding. Occasionally, a GIST may mimic a gastric lymphoma (Figs 27, 28).
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Figure 24a. Gastric non-Hodgkin lymphoma. Axial CT scans of the abdomen, obtained after intravenous contrast material administration, show circumferential thickening of the gastric wall (white arrows). A hypoattenuating area in the anterior part of the gastric wall (* in b) probably represents focal ischemia or necrosis. Multiple perigastric, mesenteric, and retroperitoneal nodes (black arrows in a) are visible. The spleen is enlarged and has displaced the left kidney anteriorly and medially.
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Figure 24b. Gastric non-Hodgkin lymphoma. Axial CT scans of the abdomen, obtained after intravenous contrast material administration, show circumferential thickening of the gastric wall (white arrows). A hypoattenuating area in the anterior part of the gastric wall (* in b) probably represents focal ischemia or necrosis. Multiple perigastric, mesenteric, and retroperitoneal nodes (black arrows in a) are visible. The spleen is enlarged and has displaced the left kidney anteriorly and medially.
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Figure 25. Gastric non-Hodgkin lymphoma. Axial contrast-enhanced CT scan shows mild thickening of the gastric wall (black arrows) and multiple enlarged nodes (white arrows), but a normal appearance of the duodenum (arrowheads).
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Figure 26. Gastric non-Hodgkin lymphoma. Axial CT scan obtained after oral contrast material administration, in a patient who recently underwent a splenectomy, shows focal and irregular thickening of the gastric wall (arrows).
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Figure 27. GISTs. Axial CT scan obtained after the administration of oral and intravenous contrast media shows a homogeneous mass with smooth margins (arrows) that has arisen in the gastric submucosa and that protrudes into the gastric lumen.
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Figure 28. GISTs. Axial CT scan obtained after the administration of oral and intravenous contrast media in another patient shows a hypervascular, heterogeneous mass that has arisen in the jejunal wall. Hypoattenuating areas in the wall (arrows) may be related to hemorrhage, ischemia, or necrosis. Note the central area of cavitation (*).
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Small Bowel.—
The small bowel is the second most common site of gastrointestinal lymphoma (27), and approximately 20% of all malignant tumors of the small bowel are lymphomas. Most cases involve non-Hodgkin lymphoma; Hodgkin disease only rarely affects the small bowel, in which it originates as part of a sprue-like syndrome (Fig 29). Steatorrhea has a higher association with Hodgkin disease. Small-bowel lymphoma usually occurs as a solitary lesion, but multiple sites are involved in 10%–25% of cases (Fig 30). Historically, the distal ileum was considered the most frequent site of involvement, presumably because of its greater amount of lymphoid tissue. However, some authors now believe that lymphoma occurs with approximately equal frequency in all parts of the small bowel (57) (Figs 31–33).
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Figure 30a. Jejunal and ileal non-Hodgkin lymphomas. Axial CT scans obtained after the administration of oral and intravenous contrast media (a–c at progressively lower levels) show diffuse and marked wall thickening of several segments of the jejunum and ileum (arrows). Despite the thickening of the bowel wall, the lumen is unobstructed.
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Figure 30b. Jejunal and ileal non-Hodgkin lymphomas. Axial CT scans obtained after the administration of oral and intravenous contrast media (a–c at progressively lower levels) show diffuse and marked wall thickening of several segments of the jejunum and ileum (arrows). Despite the thickening of the bowel wall, the lumen is unobstructed.
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Figure 30c. Jejunal and ileal non-Hodgkin lymphomas. Axial CT scans obtained after the administration of oral and intravenous contrast media (a–c at progressively lower levels) show diffuse and marked wall thickening of several segments of the jejunum and ileum (arrows). Despite the thickening of the bowel wall, the lumen is unobstructed.
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Figure 31. Jejunal and ileal non-Hodgkin lymphomas. Axial CT scan obtained after the administration of oral and intravenous contrast media in another patient shows homogeneous thickening of the wall of the distal ileum (arrowheads). The proximal ileum appears normal (arrows).
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Figure 32a. Axial CT scans acquired after the intravenous administration of a contrast medium and the oral administration of water show gastric, splenic, and ileocecal involvement in lymphoma. (a) Image obtained at the level of the upper abdomen shows focal lobulated thickening of the posterior gastric wall (arrows) and enlargement of the spleen. (b) Image obtained at the level of the pelvis and sacrum shows thickening of the ileal wall (arrowheads), a feature that is associated with intussusception of the ileum into the cecum. Pericecal nodes (arrow) also are visible. Dilated small-bowel loops (*) are suggestive of obstruction.
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Figure 32b. Axial CT scans acquired after the intravenous administration of a contrast medium and the oral administration of water show gastric, splenic, and ileocecal involvement in lymphoma. (a) Image obtained at the level of the upper abdomen shows focal lobulated thickening of the posterior gastric wall (arrows) and enlargement of the spleen. (b) Image obtained at the level of the pelvis and sacrum shows thickening of the ileal wall (arrowheads), a feature that is associated with intussusception of the ileum into the cecum. Pericecal nodes (arrow) also are visible. Dilated small-bowel loops (*) are suggestive of obstruction.
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Figure 33a. Small-bowel obstruction due to non-Hodgkin lymphoma. Axial contrast-enhanced CT scans show bowel wall thickening in a distal ileal segment (arrowheads in b) and dilatation and feces-like material in a more proximal segment (arrows in a). Free fluid also is visible in the right lower quadrant (* in b).
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Figure 33b. Small-bowel obstruction due to non-Hodgkin lymphoma. Axial contrast-enhanced CT scans show bowel wall thickening in a distal ileal segment (arrowheads in b) and dilatation and feces-like material in a more proximal segment (arrows in a). Free fluid also is visible in the right lower quadrant (* in b).
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Large Bowel.—
Colonic involvement in lymphoma is uncommon. Non-Hodgkin lymphoma is the histologic type most frequently found in this location, and its occurrence there is usually secondary to generalized disease. Primary colonic lymphomas are extremely rare and tend to arise in the cecum or rectum (50). Risk factors include immunosuppression (due to HIV infection or to immunosuppressive therapy after organ transplantation or another medical procedure) and inflammatory bowel disease (49,58–61). An important entity in the differential diagnosis is neutropenic colitis. Factors favoring a diagnosis of neutropenic colitis are contiguous involvement of the cecum and ascending colon (without involvement of other parts of the bowel) and mural stratification of the affected segment (62) (Fig 7). Large mass lymphomas in the colon may appear heterogeneous because of areas of internal necrosis, but mural stratification is unusual.
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Conclusions
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Extranodal disease is common in patients with lymphoproliferative disorders. Virtually any abdominopelvic tissue may be involved, and numerous imaging manifestations are possible. Imaging characteristics often are nonspecific and may be seen in various benign and malignant conditions.
In solid organs, lymphomatous involvement may be focal or diffuse. Typical findings in focal disease are round, well-defined, homogeneous nodules that appear hypoechoic with an absence of posterior acoustic enhancement at US; that are hypoattenuating in comparison with the organ parenchyma at CT; and that have low to intermediate signal intensity on T1-weighted MR images and moderately high signal intensity on T2-weighted images. Diffuse involvement may be difficult to detect at anatomic imaging. However, in diffuse involvement of the gastrointestinal tract, common CT findings include mild to moderate circumferential wall thickening. Luminal constriction, dilatation, or cavitation also may be observed. Lesions may be solitary or multiple and are usually homogeneous and hypo- or isoattenuating in relation to the attenuation of the normal bowel. Lymphadenopathy is usually present, and that finding aids in the diagnosis of lymphoma. Whether they occur in the solid organs or in the gastrointestinal tract, lymphomas are hypoenhancing and exert a minimal mass effect for their size.
Because some findings are nonspecific and because extranodal lymphoproliferative disease may mimic a broad spectrum of diseases and treatment-related complications, a familiarity with the features specific to lymphomas may help improve the accuracy of diagnosis and staging and thus allow better disease management.
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Footnotes
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Abbreviations: AIDS = acquired immunodeficiency syndrome, FDG = fluorodeoxyglucose, GIST = gastrointestinal stromal tumor, HIV = human immunodeficiency virus, MALT = mucosa-associated lymphoid tissue
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Abstract
LEARNING OBJECTIVES
