DOI: 10.1148/rg.233025134
(Radiographics. 2003;23:645-662.)
© RSNA, 2003
Primary Neoplasms of the Appendix: Radiologic Spectrum of Disease with Pathologic Correlation1
Perry J. Pickhardt, LCDR, MC, USNR,
Angela D. Levy, LTC, MC, USA,
Charles A. Rohrmann, Jr, MD and
Amir I. Kende, Maj, MC, USAF
1 From the Department of Radiology, National Naval Medical Center, 8901 Wisconsin Ave, Bethesda, MD 20889-5600 (P.J.P.); the Department of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md (P.J.P., A.D.L.); the Departments of Radiologic Pathology (A.D.L., C.A.R.) and Gastrointestinal Pathology (A.I.K.), Armed Forces Institute of Pathology, Washington, DC; and the Department of Radiology, University of Washington, Seattle (C.A.R.). Recipient of a Certificate of Merit award for an education exhibit at the 2001 RSNA scientific assembly. Received August 1, 2002; revision requested September 9 and received September 17; accepted September 18. Address correspondence to P.J.P. (e-mail: pjpik@hotmail.com).
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Abstract
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Although uncommon, primary appendiceal neoplasms often result in clinical symptoms that may lead to abdominal imaging. Acute appendicitis from luminal obstruction is the most common manifestation for most tumor types. Other manifestations include intussusception, a palpable mass, gastrointestinal bleeding, increasing abdominal girth (from pseudomyxoma peritonei), and secondary genitourinary complications. Asymptomatic appendiceal neoplasms may be discovered incidentally. Mucoceles from either benign or malignant mucinous neoplasms represent the majority of appendiceal tumors detected at imaging but are the least likely to manifest as appendicitis. Pseudomyxoma peritonei is a common manifestation of mucinous adenocarcinoma. Colonic-type (nonmucinous) adenocarcinoma of the appendix is much less common than mucinous tumors and typically manifests as a focal mass without mucocele formation. Carcinoid tumor is the most common appendiceal neoplasm but is less often detected radiologically because it is typically small and relatively asymptomatic. Goblet cell carcinoid tumor and non-Hodgkin lymphoma of the appendix are rare and usually infiltrate the entire appendix. Cross-sectional imaging, particularly computed tomography (CT), is effective in the evaluation of these neoplasms. CT appears to be the modality of choice whenever an appendiceal mass is suspected. CT will help rule out or confirm an appendiceal tumor and may suggest a more specific diagnosis.
© RSNA, 2003
Index Terms: Appendix, CT, 751.1211 • Appendix, neoplasms, 751.31, 751.32 • Carcinoid, 751.316 • Mucocele, 751.317
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- List the primary neoplasms that most commonly affect the vermiform appendix.
- Recognize the characteristic cross-sectional imaging features of these appendiceal neoplasms.
- Describe the role of imaging in the detection and evaluation of primary appendiceal neoplasms.
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Introduction
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Primary appendiceal neoplasms are uncommon, being found in approximately 0.5%–1.0% of appendectomy specimens at pathologic evaluation (1–3). With the exception of carcinoid tumors, most appendiceal neoplasms are seen in adults who are middle-aged or older. Mucoceles that result from cystic mucinous neoplasms account for the majority of appendiceal tumors detected at imaging, but other tumors may also be encountered (Table). Approximately 30%–50% of all appendiceal neoplasms will manifest clinically with signs and symptoms of acute appendicitis, which may lead to cross-sectional imaging (1,4, 5). Other clinical manifestations include an asymptomatic palpable mass, incidental imaging findings, intussusception, gastrointestinal bleeding, ureteral obstruction or hematuria, and increasing abdominal girth from rupture of a malignant mucocele, resulting in pseudomyxoma peritonei. Detection of these neoplasms at preoperative imaging is important because it may change the surgical approach and obviate additional surgery. In this article, we discuss the clinical, radiologic, and pathologic features of over 75 primary neoplasms of the appendix seen on images submitted to the Armed Forces Institute of Pathology over a 10-year period.
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Adenoma and Adenocarcinoma (Epithelial Neoplasms)
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Epithelial neoplasms of the appendix may be either benign (ie, adenoma) or malignant (ie, adenocarcinoma). These epithelial neoplasms are less common than appendiceal carcinoid tumors in most surgical pathology series, but they are more likely to be detected at imaging due to their larger size and higher rate of complications. It is useful to categorize these epithelial tumors as either mucinous or nonmucinous, as will become apparent from their disparate clinical, radiologic, and pathologic features.
Mucinous Epithelial Neoplasms
Unlike the typical polypoid adenomatous lesions that predominate throughout the rest of the colon and rectum, the majority of epithelial tumors of the appendix are mucin rich, demonstrate circumferential mucosal involvement, and have a strong propensity to form mucoceles (5). The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus; it does not constitute a pathologic diagnosis and can be caused by a variety of nonneoplastic, benign neoplastic, and malignant conditions. Although mucinous neoplasms of the appendix are by far the most common cause of mucoceles, these terms—mucinous neoplasm and mucocele—cannot be used interchangeably without qualification. Interestingly, mucoceles resulting from nonneoplastic occlusion (simple retention cysts) rarely exceed 2 cm in diameter (5,6). Mucoceles larger than 2 cm that are initially diagnosed as simple mucoceles are more likely to represent benign neoplasms that have been undersampled.
A variety of terms have been used to describe benign mucinous neoplasms of the appendix, including adenoma, cystadenoma, benign neoplastic mucocele, and so on. The descriptive term mucinous will often precede these terms. Analogous terms have been used for malignant neoplasms (eg, mucinous cystadenocarcinoma). Furthermore, tumors that cannot be clearly classified as benign or malignant may be classified as mucinous tumors of uncertain malignant potential (5,6). Regardless of whether they are benign or malignant, the vast majority of mucinous neoplasms that are resected have formed mucoceles. Benign mucinous tumors are cured with simple excision (appendectomy); malignant lesions, if resectable, require right hemicolectomy (1,7).
Most benign mucoceles due to mucinous adenomas are relatively asymptomatic and are found incidentally at physical examination as a palpable mass or at abdominal imaging. Symptomatic manifestation from superinfection of a mucocele can be clinically indistinguishable from nontumoral acute appendicitis. However, mucinous neoplasms are less likely to manifest with appendicitis than are most other appendiceal neoplasms (4), which may be related to the fact that mucoceles result from chronic luminal obstruction, whereas acute inflammation of these lesions generally requires superinfection. Other symptomatic manifestations include intussusception, torsion, and right ureteral obstruction (2). Unlike mucinous adenomas, the majority of mucinous adenocarcinomas produce symptoms that lead to their eventual diagnosis (2,7). Clinical manifestations may have any of the causes listed previously for benign neoplastic mucoceles but may also have malignant causes such as direct invasion of an adjacent organ or increasing abdominal girth from tumor extension into the peritoneal cavity (pseudomyxoma peritonei) (6,8).
When used in an unqualified manner, the term pseudomyxoma peritonei is fraught with ambiguity (6). It generally describes intraperitoneal accumulation of gelatinous material, typically as a diffuse process, but is sometimes used to describe localized collections from rupture of a benign mucocele. However, the diffuse form involves proliferation of viable neoplastic cells throughout the peritoneum and implies a malignant cause (6). Some investigators posit that nearly all true cases are appendiceal in origin and that associated ovarian lesions usually represent metastatic disease, although this is controversial (6,8). The clinical course of diffuse pseudomyxoma peritonei is typically insidious and unrelenting, with a 5-year survival rate approaching 65% (6). Treatment usually consists of surgical debulking with appendectomy, omentectomy, and, in women, bilateral oophorectomy. Intraperitoneal chemotherapy may be of benefit to some patients (8).
Imaging Features.—
The imaging diagnosis of mucinous neoplasms hinges primarily on detection of the resulting mucocele. Abdominal radiography may suggest a soft-tissue mass in the right lower quadrant, but specificity is increased when calcification is identified. Curvilinear mural calcification is highly suggestive of the diagnosis (Fig 1) but is seen in less than 50% of cases (9,10). At contrast enema examination, mucoceles cause a smooth impression on the medial aspect of the cecum, a finding that suggests an extramucosal or extrinsic process (Figs 2, 3). However, the typical location of the filling defect will usually favor an appendiceal process. Analogous findings are seen at endoscopy, but, as with contrast enema examination, the overall size and morphologic features cannot be assessed (Fig 3a–3c). Cross-sectional imaging (CT, ultrasonography [US], or magnetic resonance [MR] imaging) is useful for evaluating the full extent of the lesion in this setting (Fig 3d).
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Figure 1a. Asymptomatic appendiceal mucocele from mucinous adenoma in a 77-year-old man. (a) Abdominal radiograph collimated to the right lower quadrant shows coarse curvilinear calcification (arrows) overlying the right iliac wing. An associated rounded mass (arrowheads) is suggested. (b) Axial contrast material-enhanced computed tomographic (CT) scan shows a cystic lesion with mural calcification (M) in the expected region of the appendix. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin [H-E] stain) shows a collapsed lumen (*) lined by undulating and flattened dysplastic epithelium (arrowheads), as well as fibrosis of the wall.
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Figure 1b. Asymptomatic appendiceal mucocele from mucinous adenoma in a 77-year-old man. (a) Abdominal radiograph collimated to the right lower quadrant shows coarse curvilinear calcification (arrows) overlying the right iliac wing. An associated rounded mass (arrowheads) is suggested. (b) Axial contrast material-enhanced computed tomographic (CT) scan shows a cystic lesion with mural calcification (M) in the expected region of the appendix. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin [H-E] stain) shows a collapsed lumen (*) lined by undulating and flattened dysplastic epithelium (arrowheads), as well as fibrosis of the wall.
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Figure 1c. Asymptomatic appendiceal mucocele from mucinous adenoma in a 77-year-old man. (a) Abdominal radiograph collimated to the right lower quadrant shows coarse curvilinear calcification (arrows) overlying the right iliac wing. An associated rounded mass (arrowheads) is suggested. (b) Axial contrast material-enhanced computed tomographic (CT) scan shows a cystic lesion with mural calcification (M) in the expected region of the appendix. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin [H-E] stain) shows a collapsed lumen (*) lined by undulating and flattened dysplastic epithelium (arrowheads), as well as fibrosis of the wall.
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Figure 2a. Asymptomatic appendiceal mucocele from mucinous adenoma in a 62-year-old man. (a) Photograph obtained during colonoscopy shows a smooth mass (M) protruding into the cecum. (b) Radiograph from a solid-column contrast enema examination shows a smooth, broad-based filling defect (arrowhead). (c) Axial contrast-enhanced CT scan demonstrates the cecal filling defect (arrowhead). (d) Axial contrast-enhanced CT scan shows the full extent of the mucocele (arrow).
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Figure 2b. Asymptomatic appendiceal mucocele from mucinous adenoma in a 62-year-old man. (a) Photograph obtained during colonoscopy shows a smooth mass (M) protruding into the cecum. (b) Radiograph from a solid-column contrast enema examination shows a smooth, broad-based filling defect (arrowhead). (c) Axial contrast-enhanced CT scan demonstrates the cecal filling defect (arrowhead). (d) Axial contrast-enhanced CT scan shows the full extent of the mucocele (arrow).
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Figure 2c. Asymptomatic appendiceal mucocele from mucinous adenoma in a 62-year-old man. (a) Photograph obtained during colonoscopy shows a smooth mass (M) protruding into the cecum. (b) Radiograph from a solid-column contrast enema examination shows a smooth, broad-based filling defect (arrowhead). (c) Axial contrast-enhanced CT scan demonstrates the cecal filling defect (arrowhead). (d) Axial contrast-enhanced CT scan shows the full extent of the mucocele (arrow).
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Figure 2d. Asymptomatic appendiceal mucocele from mucinous adenoma in a 62-year-old man. (a) Photograph obtained during colonoscopy shows a smooth mass (M) protruding into the cecum. (b) Radiograph from a solid-column contrast enema examination shows a smooth, broad-based filling defect (arrowhead). (c) Axial contrast-enhanced CT scan demonstrates the cecal filling defect (arrowhead). (d) Axial contrast-enhanced CT scan shows the full extent of the mucocele (arrow).
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Figure 3. Asymptomatic appendiceal mucocele from mucinous adenoma in a 53-year-old man. Spot radiograph from an air-contrast barium enema examination shows a smooth filling defect (M) that appears to be submucosal. The acute angles formed with the adjacent cecal wall may represent early intussusception.
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At US, an ovoid cystic mass with or without acoustic shadowing from dystrophic mural calcification is characteristic of mucoceles from mucinous neoplasms (Fig 4) (11). The intraluminal echotexture can have a variable appearance, but low-level internal echoes are somewhat typical. A pear-shaped or chicken drumstick appearance may be appreciated in some cases due to lesser dilatation of a portion of the appendix (Fig 4). Identification of a separate right ovary in women is crucial for excluding processes such as a cystic ovarian neoplasm or tubo-ovarian abscess. The differential diagnosis might also include periappendiceal abscess, enteric duplication cyst, mesenteric cyst, and hydrosalpinx.
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Figure 4a. Appendiceal mucocele from mucinous adenoma in a 57-year-old man with a palpable abdominal mass in the right lower quadrant. (a) Transabdominal US image shows a cystic lesion with a "chicken drumstick" appearance. (b) Photograph of the surgically resected specimen shows the dilated appendix extending inferiorly from the base of the cecum.
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Figure 4b. Appendiceal mucocele from mucinous adenoma in a 57-year-old man with a palpable abdominal mass in the right lower quadrant. (a) Transabdominal US image shows a cystic lesion with a "chicken drumstick" appearance. (b) Photograph of the surgically resected specimen shows the dilated appendix extending inferiorly from the base of the cecum.
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CT is ideal for evaluating mucoceles of the appendix because it has certain advantages over other imaging modalities. The anatomic relationship between the elongated cystic mass and the cecum is usually more apparent at CT than at US (Fig 5a), and CT is more sensitive than radiography in detecting mural calcification. Inadequate opacification of the ileocecal region with enteric contrast material is a recognized cause of false- positive and false-negative findings at CT (10). MR imaging recapitulates the CT finding of a cystic mass (Fig 5b, 5c), but calcification will be less apparent (12).
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Figure 5a. Mucocele from mucinous adenoma in a 47-year-old man with nonspecific abdominal pain. (a) Axial CT scan shows an elongated cystic mass (M) in the expected region of the appendix. (b, c) Sagittal T2-weighted (b) and contrast-enhanced fat-suppressed T1-weighted (c) MR images show the same elongated cystic mass (M). (d) Photograph of the gross specimen shows fusiform dilatation of the appendix.
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Figure 5b. Mucocele from mucinous adenoma in a 47-year-old man with nonspecific abdominal pain. (a) Axial CT scan shows an elongated cystic mass (M) in the expected region of the appendix. (b, c) Sagittal T2-weighted (b) and contrast-enhanced fat-suppressed T1-weighted (c) MR images show the same elongated cystic mass (M). (d) Photograph of the gross specimen shows fusiform dilatation of the appendix.
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Figure 5c. Mucocele from mucinous adenoma in a 47-year-old man with nonspecific abdominal pain. (a) Axial CT scan shows an elongated cystic mass (M) in the expected region of the appendix. (b, c) Sagittal T2-weighted (b) and contrast-enhanced fat-suppressed T1-weighted (c) MR images show the same elongated cystic mass (M). (d) Photograph of the gross specimen shows fusiform dilatation of the appendix.
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Figure 5d. Mucocele from mucinous adenoma in a 47-year-old man with nonspecific abdominal pain. (a) Axial CT scan shows an elongated cystic mass (M) in the expected region of the appendix. (b, c) Sagittal T2-weighted (b) and contrast-enhanced fat-suppressed T1-weighted (c) MR images show the same elongated cystic mass (M). (d) Photograph of the gross specimen shows fusiform dilatation of the appendix.
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Atypical cross-sectional imaging features may reflect a secondary complication, malignancy, or an unusual pathologic variation. Soft-tissue thickening and irregularity of the mucocele wall and surrounding fat are nonspecific findings that suggest malignancy, secondary inflammation, or both (Figs 6–8) (13). Intraluminal gas bubbles or an air-fluid level within a mucocele are generally diagnostic for superinfection, which can complicate both benign and malignant mucoceles (Figs 7, 8). Myxoglobulosis is a rare mucocele variant consisting of multiple intraluminal pearly spherules that may be apparent at radiography or CT if they are calcified (Fig 9) (14). Intussusception into the colon is an uncommon but recognized manifestation of appendiceal mucoceles. Suggestive imaging findings may be apparent on abdominal radiographs, and intussusception can be confirmed at contrast enema examination, but specificity is greatly increased with identification of a cystic lead mass at CT (Fig 10). Genitourinary symptoms such as right ureteral obstruction or bladder compromise may result in an atypical manifestation (Fig 11).
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Figure 6a. Mucinous adenocarcinoma of the appendix in a 68-year-old woman with acute right lower quadrant pain. (a) Axial unenhanced CT scan shows a complex heterogeneous mass in the right lower quadrant (arrowhead). (b) US image shows a thick-walled cystic lesion with a complex internal architecture (arrowhead). (c) Photograph of the cut gross specimen shows internal polypoid tumor nodules that correspond to the complex mass identified at cross-sectional imaging. Scale is in centimeters. (d) Photomicrograph (original magnification, x100; H-E stain) shows lightly basophilic mucin pools (*) lined by columnar glandular epithelium (arrow) and extending below the surface epithelium (arrowheads).
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Figure 6b. Mucinous adenocarcinoma of the appendix in a 68-year-old woman with acute right lower quadrant pain. (a) Axial unenhanced CT scan shows a complex heterogeneous mass in the right lower quadrant (arrowhead). (b) US image shows a thick-walled cystic lesion with a complex internal architecture (arrowhead). (c) Photograph of the cut gross specimen shows internal polypoid tumor nodules that correspond to the complex mass identified at cross-sectional imaging. Scale is in centimeters. (d) Photomicrograph (original magnification, x100; H-E stain) shows lightly basophilic mucin pools (*) lined by columnar glandular epithelium (arrow) and extending below the surface epithelium (arrowheads).
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Figure 6c. Mucinous adenocarcinoma of the appendix in a 68-year-old woman with acute right lower quadrant pain. (a) Axial unenhanced CT scan shows a complex heterogeneous mass in the right lower quadrant (arrowhead). (b) US image shows a thick-walled cystic lesion with a complex internal architecture (arrowhead). (c) Photograph of the cut gross specimen shows internal polypoid tumor nodules that correspond to the complex mass identified at cross-sectional imaging. Scale is in centimeters. (d) Photomicrograph (original magnification, x100; H-E stain) shows lightly basophilic mucin pools (*) lined by columnar glandular epithelium (arrow) and extending below the surface epithelium (arrowheads).
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Figure 6d. Mucinous adenocarcinoma of the appendix in a 68-year-old woman with acute right lower quadrant pain. (a) Axial unenhanced CT scan shows a complex heterogeneous mass in the right lower quadrant (arrowhead). (b) US image shows a thick-walled cystic lesion with a complex internal architecture (arrowhead). (c) Photograph of the cut gross specimen shows internal polypoid tumor nodules that correspond to the complex mass identified at cross-sectional imaging. Scale is in centimeters. (d) Photomicrograph (original magnification, x100; H-E stain) shows lightly basophilic mucin pools (*) lined by columnar glandular epithelium (arrow) and extending below the surface epithelium (arrowheads).
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Figure 7. Infected mucocele from a mucinous appendiceal neoplasm manifesting as acute appendicitis in a 61-year-old man with acute right lower quadrant pain and leukocytosis. Axial contrast-enhanced CT scan shows a complex, thick-walled cystic mass (arrowhead). There is an extensive soft-tissue component, infiltration of the adjacent fat, and a tiny gas bubble (arrow). Histologic analysis showed these findings to represent a benign mucinous adenoma.
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Figure 8. Infected mucocele from a mucinous appendiceal neoplasm manifesting as acute appendicitis in a 34-year-old woman with acute right lower quadrant pain. Axial contrast-enhanced CT scan shows a thick-walled cystic mass (arrows) adjacent to the cecum. There are gas bubbles surrounding the luminal fluid. Although similar in appearance to the lesion in Figure 7, the underlying neoplasm in this case was malignant (mucinous adenocarcinoma).
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Figure 9a. Myxoglobulosis in an asymptomatic mucocele from mucinous adenoma in a 51-year-old man. The neoplasm was found initially at contrast enema examination. (a) Axial contrast-enhanced CT scan shows a mucocele with rim calcification (arrowheads) and multiple small, rounded intraluminal hyperattenuating areas. (b) Photograph of the sectioned gross specimen shows multiple intraluminal pearly spherules (arrowheads), one of which has been extruded (arrow).
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Figure 9b. Myxoglobulosis in an asymptomatic mucocele from mucinous adenoma in a 51-year-old man. The neoplasm was found initially at contrast enema examination. (a) Axial contrast-enhanced CT scan shows a mucocele with rim calcification (arrowheads) and multiple small, rounded intraluminal hyperattenuating areas. (b) Photograph of the sectioned gross specimen shows multiple intraluminal pearly spherules (arrowheads), one of which has been extruded (arrow).
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Figure 10a. Appendiceal mucocele from mucinous adenoma manifesting as intussusception in a 39-year-old woman. (a) Abdominal radiograph shows a rounded mass (arrow) that projects into the lumen of the transverse colon, a finding that suggests intussusception. There is faint rim calcification along the leading edge of the mass. (b) Image from a contrast enema examination helps confirm the intussusception, which has been partially reduced (cf a). A rounded lead mass (M) is also present. (c) Axial contrast-enhanced CT scan shows the cystic lead mass (M) and mesenteric fat and vessels (arrow) of the intussusceptum.
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Figure 10b. Appendiceal mucocele from mucinous adenoma manifesting as intussusception in a 39-year-old woman. (a) Abdominal radiograph shows a rounded mass (arrow) that projects into the lumen of the transverse colon, a finding that suggests intussusception. There is faint rim calcification along the leading edge of the mass. (b) Image from a contrast enema examination helps confirm the intussusception, which has been partially reduced (cf a). A rounded lead mass (M) is also present. (c) Axial contrast-enhanced CT scan shows the cystic lead mass (M) and mesenteric fat and vessels (arrow) of the intussusceptum.
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Figure 10c. Appendiceal mucocele from mucinous adenoma manifesting as intussusception in a 39-year-old woman. (a) Abdominal radiograph shows a rounded mass (arrow) that projects into the lumen of the transverse colon, a finding that suggests intussusception. There is faint rim calcification along the leading edge of the mass. (b) Image from a contrast enema examination helps confirm the intussusception, which has been partially reduced (cf a). A rounded lead mass (M) is also present. (c) Axial contrast-enhanced CT scan shows the cystic lead mass (M) and mesenteric fat and vessels (arrow) of the intussusceptum.
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Figure 11. Partial ureteral obstruction from a benign mucocele (mucinous adenoma) in a 74-year-old man with a history of transitional cell carcinoma of the bladder. Abdominal radiograph obtained after retrograde injection of contrast material into the right upper collecting system shows narrowing and partial obstruction of the ureter at the level of an adjacent rounded soft-tissue mass with faint rim calcification (arrowheads).
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Finally, a substantial subset of patients with mucinous adenocarcinoma will present with slowly increasing abdominal girth from pseudomyxoma peritonei caused by prior mucocele rupture or transmural extension. Typical imaging features include widespread heterogeneous peritoneal locules that displace and distort the hollow viscera (Fig 12) or produce a scalloping effect on the solid organs (Fig 13) (15). Linear or punctate septal calcification may be apparent at CT (Fig 13). In some cases, the primary appendiceal tumor will still be apparent (Fig 14).
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Figure 12. Pseudomyxoma peritonei from mucinous adenocarcinoma of the appendix manifesting as increasing abdominal girth in a 49-year-old man. Axial contrast-enhanced CT scan shows mass effect on and distortion of the bowel caused by diffuse intraperitoneal locules of varying attenuation. Omental caking is also present.
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Figure 13. Pseudomyxoma peritonei from mucinous adenocarcinoma of the appendix manifesting as increasing abdominal girth in a 49-year-old woman. Axial contrast-enhanced CT scan shows scalloping of the liver and spleen by intraperitoneal mucin. There are multiple areas of septal calcification (arrowheads).
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Figure 14. Pseudomyxoma peritonei in a 51-year-old man. Axial contrast-enhanced CT scan shows intraperitoneal mucin and a thick-walled appendiceal mucocele with mural calcification (arrowhead), findings that represent a primary mucinous adenocarcinoma of the appendix.
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Histologic Features.—
Unlike adenomas seen elsewhere in the large intestine, adenomas of the appendix are typically composed of mucin-rich epithelium and demonstrate a villous architecture (5,6). Moreover, these neoplasms tend to be low grade with circumferential involvement of the appendix. As these lesions grow, the villi become shorter and demonstrate more of an undulating growth pattern (Fig 1c). Progressive growth to mucocele formation results in wall thinning and fibrosis of the submucosa, lamina propria, and muscularis propria.
The presence of invasive neoplastic cells beyond the muscularis mucosae is diagnostic for adenocarcinoma (Fig 6d). The presence of acellular mucin within the appendiceal wall is not in itself diagnostic for malignancy and can be seen with some adenomas. Mucinous lesions that cannot be classified at the Armed Forces Institute of Pathology as clearly benign or malignant are considered to have uncertain malignant potential. A mucinous adenocarcinoma can be distinguished from the much rarer colonic-type adenocarcinoma of the appendix in that at least 50% of the lesion is composed of mucin (5,6). Most adenocarcinomas of the appendix probably evolve through an adenoma-carcinoma sequence, similar to other colonic neoplasms (6).
Colonic-type (Nonmucinous) Epithelial Neoplasms
The nonmucinous adenomas and adenocarcinomas that are characteristic of colorectal neoplasia rarely occur in the appendix. In one large pathology series, the relative frequency of colonic-type appendiceal neoplasms was 2% and 7% among adenomas and adenocarcinomas, respectively; the remaining tumors were mucinous (5). Other studies have reported up to a 2:1 ratio of mucinous to colonic-type adenocarcinomas (7). The latter tend not to form mucoceles, and most manifest clinically with appendicitis related to malignant luminal obstruction (4,7).
Imaging Features.—
Relatively little information exists on the imaging appearance of colonic-type neoplasms of the appendix. In our experience, the majority of cases detected at imaging will be malignant (adenocarcinoma), usually in the setting of suspected appendicitis in an older individual (4). At CT, a focal soft-tissue mass that involves the appendix but demonstrates no mucocele formation is most characteristic, a finding that underscores the dissimilarity between mucinous and nonmucinous neoplasms (Figs 15, 16). A subtle infiltrative appendiceal mass with surrounding periappendiceal inflammation may be mistaken for nontumoral appendicitis. Direct invasion of adjacent organs may manifest as clinical symptoms in some cases (Fig 17).
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Figure 15a. Colonic-type (nonmucinous) adenocarcinoma of the appendix manifesting as acute appendicitis in an 88-year-old man with acute right lower quadrant pain and leukocytosis. (a) Axial contrast-enhanced CT scan shows a soft-tissue mass with no mucocele formation (arrowhead). The mass is seen to replace the appendix. Note the soft-tissue mound at the appendiceal orifice. (b) Photomicrograph (original magnification, x100; H-E stain) shows infiltrating neoplastic glands (arrow) with luminal necrosis (*).
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Figure 15b. Colonic-type (nonmucinous) adenocarcinoma of the appendix manifesting as acute appendicitis in an 88-year-old man with acute right lower quadrant pain and leukocytosis. (a) Axial contrast-enhanced CT scan shows a soft-tissue mass with no mucocele formation (arrowhead). The mass is seen to replace the appendix. Note the soft-tissue mound at the appendiceal orifice. (b) Photomicrograph (original magnification, x100; H-E stain) shows infiltrating neoplastic glands (arrow) with luminal necrosis (*).
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Figure 16a. Colonic-type (nonmucinous) adenocarcinoma of the appendix manifesting as acute appendicitis in a 33-year-old man with acute abdominal pain and leukocytosis. (a) Axial unenhanced CT scan shows a focal soft-tissue mass (arrow) that involves the tip of a long, retrocecal appendix. Note the soft-tissue infiltration of the surrounding fat. (b) On an axial unenhanced CT scan, the proximal portion of the appendix (arrow) appears normal.
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Figure 16b. Colonic-type (nonmucinous) adenocarcinoma of the appendix manifesting as acute appendicitis in a 33-year-old man with acute abdominal pain and leukocytosis. (a) Axial unenhanced CT scan shows a focal soft-tissue mass (arrow) that involves the tip of a long, retrocecal appendix. Note the soft-tissue infiltration of the surrounding fat. (b) On an axial unenhanced CT scan, the proximal portion of the appendix (arrow) appears normal.
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Figure 17a. Colonic-type adenocarcinoma of the appendix in a 38-year-old man with hematuria from bladder invasion. (a) Axial contrast-enhanced CT scan shows a thickened appendix (A) with an expansile soft-tissue mass (arrowheads) that extends from the distal aspect of the appendix and continues inferiorly. (b) Axial contrast-enhanced CT scan shows direct invasion of the urinary bladder by the mass (arrow).
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Figure 17b. Colonic-type adenocarcinoma of the appendix in a 38-year-old man with hematuria from bladder invasion. (a) Axial contrast-enhanced CT scan shows a thickened appendix (A) with an expansile soft-tissue mass (arrowheads) that extends from the distal aspect of the appendix and continues inferiorly. (b) Axial contrast-enhanced CT scan shows direct invasion of the urinary bladder by the mass (arrow).
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Histologic Features.—
Colonic-type (nonmucinous) adenocarcinomas of the appendix are defined as malignant tumors in which less than 50% of the lesion is composed of mucin (5). These lesions are rare within the appendix and appear as cuboidal or columnar neoplastic cells that form infiltrating glands resembling typical adenocarcinomas of the colon and rectum (Fig 15b) (5). They are typically more focal than mucinous neoplasms and tend not to form mucoceles.
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Carcinoid Tumors
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Classic Carcinoid Tumors
Classic carcinoid tumors of the appendix derive from subepithelial neuroendocrine cells and may represent up to 80% of all appendiceal neoplasms (2,16). Unlike with most other primary appendiceal neoplasms, its discovery at surgery or pathologic examination is most often serendipitous. Even in the setting of acute appendicitis, a coexisting carcinoid tumor is the obstructing cause in only 25% of cases, reflecting the fact that over 70% are found in the distal third of the appendix (away from the base) and are less than 1 cm in size (2,17). Patient age at diagnosis is also unique in appendiceal carcinoid tumors, which are often seen in young adults (4,16,18). It remains unclear why the appendix is the most common site for gastrointestinal carcinoid tumors and why these tumors demonstrate a uniquely indolent clinical course in this location (5-year survival rate >90%) compared with carcinoid tumors elsewhere along the gastrointestinal tract. Although all carcinoid tumors are considered potentially malignant, metastatic disease and carcinoid syndrome with an appendiceal primary site are exceedingly rare. Studies have shown that tumor size correlates well with prognosis and that simple appendectomy is sufficient for most carcinoid tumors less than 1.5–2.0 cm in size (17). Tumors greater than 2 cm are less common but should be considered malignant and generally require right hemicolectomy (2,17).
Imaging Features.—
The relative paucity of imaging findings in the majority of appendiceal carcinoid tumors reflects the typical small size, confinement to the distal appendix, and low complication rate of these tumors. Consequently, although these tumors are the most common of all appendiceal neoplasms, they account for less than 10% of cases submitted to the radiologic archives at the Armed Forces Institute of Pathology over the past 10 years. A symptomatic obstructing carcinoid tumor near the base of the appendix will usually manifest at CT or US as appendicitis; the tumor itself may not always be appreciated (Fig 18) (19). Mucocele formation may also occur but is a rare finding (20). The tumor itself may be discernible on imaging studies when it is of sufficient size or demonstrates calcification, which may mimic a nontumoral appendicolith. Appendiceal carcinoid tumors sometimes demonstrate a diffuse infiltrative pattern that manifests as diffuse mural thickening at cross-sectional imaging. Although rare, metastatic disease has CT features similar to those of small bowel carcinoid tumors. An irregular soft-tissue mass near the root of the mesentery is characteristic (Fig 19).
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Figure 18a. Appendiceal carcinoid tumor manifesting as obstructive appendicitis in a 6-year-old boy. (a) Longitudinal US image of the right lower quadrant shows a dilated, noncompressible appendix (arrowheads) with striated wall thickening and intraluminal gas echoes. No obvious mass was appreciated at the base of the appendix. (b) Photograph of the gross specimen sectioned at the appendiceal base shows a rounded, subcentimeter carcinoid tumor (arrowheads), which produced the luminal obstruction. (c) Photomicrograph (original magnification, x400; H-E stain) shows cords and glands of endocrine cells with small nucleoli and stippled chromatin (arrows).
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Figure 18b. Appendiceal carcinoid tumor manifesting as obstructive appendicitis in a 6-year-old boy. (a) Longitudinal US image of the right lower quadrant shows a dilated, noncompressible appendix (arrowheads) with striated wall thickening and intraluminal gas echoes. No obvious mass was appreciated at the base of the appendix. (b) Photograph of the gross specimen sectioned at the appendiceal base shows a rounded, subcentimeter carcinoid tumor (arrowheads), which produced the luminal obstruction. (c) Photomicrograph (original magnification, x400; H-E stain) shows cords and glands of endocrine cells with small nucleoli and stippled chromatin (arrows).
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Figure 18c. Appendiceal carcinoid tumor manifesting as obstructive appendicitis in a 6-year-old boy. (a) Longitudinal US image of the right lower quadrant shows a dilated, noncompressible appendix (arrowheads) with striated wall thickening and intraluminal gas echoes. No obvious mass was appreciated at the base of the appendix. (b) Photograph of the gross specimen sectioned at the appendiceal base shows a rounded, subcentimeter carcinoid tumor (arrowheads), which produced the luminal obstruction. (c) Photomicrograph (original magnification, x400; H-E stain) shows cords and glands of endocrine cells with small nucleoli and stippled chromatin (arrows).
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Figure 19a. Metastatic appendiceal carcinoid tumor with an infiltrative growth pattern in a 26-year-old woman. (a) Axial contrast-enhanced CT scan shows a poorly defined soft-tissue mass with a focus of eccentric calcification located near the root of the mesentery (arrowhead). (b) Axial contrast-enhanced CT scan obtained inferior to a shows diffuse wall thickening of the appendix (arrowhead) from the infiltrating primary appendiceal carcinoid tumor.
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Figure 19b. Metastatic appendiceal carcinoid tumor with an infiltrative growth pattern in a 26-year-old woman. (a) Axial contrast-enhanced CT scan shows a poorly defined soft-tissue mass with a focus of eccentric calcification located near the root of the mesentery (arrowhead). (b) Axial contrast-enhanced CT scan obtained inferior to a shows diffuse wall thickening of the appendix (arrowhead) from the infiltrating primary appendiceal carcinoid tumor.
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Histologic Features.—
Carcinoid tumors are composed of small cells with uniform round nuclei that contain stippled chromatin but are without prominent nucleoli (Fig 18c). There is usually no significant mitotic activity, cytologic atypia, or nuclear pleomorphism (20). Recognized growth patterns include insular, trabecular, glandular, and diffuse patterns. Use of silver stains and immunohistochemical studies improve the specificity of diagnosis in difficult cases (20).
Tubular Carcinoid Tumors
Tubular carcinoid tumors are rare variants of classic carcinoid tumors. However, the distinction between the two is purely histologic; their clinical behavior is quite similar (6). Tubular carcinoid tumors are characteristically seen in younger patients, tend to be small and localized to the appendiceal tip, rarely metastasize, and have a favorable prognosis. The imaging findings in tubular carcinoid tumors are not well documented; however, given the aforementioned features, the tumor should resemble a small classic carcinoid tumor. At histologic analysis, tubular carcinoid tumors are characterized by small, uniform groups of cells that form tubular structures within an abundant stroma (6). These lesions can generally be treated as classic carcinoid tumors.
Goblet Cell Carcinoid Tumors
Goblet cell carcinoid tumors are unusual tumors that are nearly exclusive to the appendix and likely represent an entity that is intermediate between adenocarcinoma and classic carcinoid tumor (6). The terms adenocarcinoid and goblet cell carcinoid have been used interchangeably in the past. However, the former term has been omitted from the current World Health Organization (WHO) classification scheme because it also applies to tubular carcinoid tumors, which are clinically and pathologically distinct. Goblet cell carcinoid tumors are best considered a low-grade malignancy, so that most patients will undergo right hemicolectomy. At gross pathologic examination, goblet cell carcinoid tumors are infiltrative and typically involve the entire appendix circumferentially. If no discrete tumor nodules or mass is evident, the diagnosis can often be made only at microscopic examination. Not infrequently, frank mucinous adenocarcinoma will develop within a goblet cell carcinoid tumor (5). Metastatic spread is most often due to direct peritoneal extension (6).
Imaging Features.—
Cross-sectional imaging findings will typically reflect the infiltrative nature of the tumor, with often mild but diffuse mural thickening (Fig 20). The propensity of advanced tumors to metastasize to the ovaries and peritoneum has also been demonstrated at cross-sectional imaging (Fig 21).
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Figure 20a. Subtle infiltrative goblet cell carcinoid tumor of the appendix manifesting as acute appendicitis in a 39-year-old man. (a) Axial contrast-enhanced CT scan shows mild diffuse wall thickening of the appendix (arrowhead) with apparent intraluminal fluid or debris. (b) Photograph of the sectioned gross specimen shows that the "intraluminal" material seen at CT actually represents mural thickening from an infiltrative tumor that obliterates the lumen (arrow). (c) Photomicrograph (original magnification, x400; H-E stain) shows nests of goblet cells (arrow) separated by stroma.
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Figure 20b. Subtle infiltrative goblet cell carcinoid tumor of the appendix manifesting as acute appendicitis in a 39-year-old man. (a) Axial contrast-enhanced CT scan shows mild diffuse wall thickening of the appendix (arrowhead) with apparent intraluminal fluid or debris. (b) Photograph of the sectioned gross specimen shows that the "intraluminal" material seen at CT actually represents mural thickening from an infiltrative tumor that obliterates the lumen (arrow). (c) Photomicrograph (original magnification, x400; H-E stain) shows nests of goblet cells (arrow) separated by stroma.
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Figure 20c. Subtle infiltrative goblet cell carcinoid tumor of the appendix manifesting as acute appendicitis in a 39-year-old man. (a) Axial contrast-enhanced CT scan shows mild diffuse wall thickening of the appendix (arrowhead) with apparent intraluminal fluid or debris. (b) Photograph of the sectioned gross specimen shows that the "intraluminal" material seen at CT actually represents mural thickening from an infiltrative tumor that obliterates the lumen (arrow). (c) Photomicrograph (original magnification, x400; H-E stain) shows nests of goblet cells (arrow) separated by stroma.
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Figure 21a. Metastatic goblet cell carcinoid tumor of the appendix in a 38-year-old woman. (a) Axial contrast-enhanced CT scan shows a large, enhancing pelvic mass (M) that encases the ovaries, making determination of appendiceal origin difficult. (b) Axial contrast-enhanced CT scan obtained cephalad to a demonstrates intraperitoneal spread (arrowheads).
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Figure 21b. Metastatic goblet cell carcinoid tumor of the appendix in a 38-year-old woman. (a) Axial contrast-enhanced CT scan shows a large, enhancing pelvic mass (M) that encases the ovaries, making determination of appendiceal origin difficult. (b) Axial contrast-enhanced CT scan obtained cephalad to a demonstrates intraperitoneal spread (arrowheads).
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Histologic Features.—
Goblet cells are characterized by the accumulation of mucous secretory granules, which appear as abundant clear mucin–filled cytoplasm (6). Small groups of these cells in the form of clusters or strands diffusely infiltrate the appendiceal wall, often circumferentially (Fig 20c). Smaller numbers of endocrine cells are present among these clusters of goblet cells and are best demonstrated with immunoexpression of neuroendocrine markers.
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Lymphoma
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Although the gastrointestinal tract is the most common site for extranodal non-Hodgkin lymphoma, appendiceal lymphoma is rare (21,22). Nevertheless, when lymphoma does involve the appendix, it tends to cause symptoms (23). The most common clinical manifestation is acute appendicitis, which may be the first and only indication of disease. The appendix can become massively enlarged but typically maintains its vermiform appearance (23). To our knowledge, all reported cases of appendiceal lymphoma have proved to be non-Hodgkin lymphoma.
Imaging Features
The existing literature on the imaging appearance of appendiceal lymphoma is mainly limited to case reports (24,25). In our experience, however, all cases have demonstrated prominent enlargement of the appendix with relative maintenance of its vermiform appearance (Fig 22) (23). If its blind-ending nature is not appreciated, the abnormal appendix could be mistaken for an abnormal small bowel loop or an extraintestinal process such as lymphadenopathy (Fig 23). Diffuse mural thickening is typically hypoechoic at US (Fig 22) and has soft-tissue attenuation at CT (Fig 23). The hypoechoic appearance at US may mimic the cystic dilatation seen in mucoceles of the appendix (Fig 22). Aneurysmal dilatation of the appendiceal lumen may be an important associated finding (23).
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Figure 22a. Non-Hodgkin lymphoma of the appendix in a 66-year-old man with lower gastrointestinal bleeding. (a) Image from a barium enema examination shows a broad cecal filling defect with partial opacification of the appendiceal lumen (arrowhead). (b) US image obtained over the right lower quadrant shows prominent hypoechoic vermiform enlargement of the appendix (A). The diffuse hypoechoic appearance mimics that of a cystic mucocele. (c) Photomicrograph (original magnification, x400; H-E stain) shows monotonous lymphocytic infiltration.
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Figure 22b. Non-Hodgkin lymphoma of the appendix in a 66-year-old man with lower gastrointestinal bleeding. (a) Image from a barium enema examination shows a broad cecal filling defect with partial opacification of the appendiceal lumen (arrowhead). (b) US image obtained over the right lower quadrant shows prominent hypoechoic vermiform enlargement of the appendix (A). The diffuse hypoechoic appearance mimics that of a cystic mucocele. (c) Photomicrograph (original magnification, x400; H-E stain) shows monotonous lymphocytic infiltration.
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Figure 22c. Non-Hodgkin lymphoma of the appendix in a 66-year-old man with lower gastrointestinal bleeding. (a) Image from a barium enema examination shows a broad cecal filling defect with partial opacification of the appendiceal lumen (arrowhead). (b) US image obtained over the right lower quadrant shows prominent hypoechoic vermiform enlargement of the appendix (A). The diffuse hypoechoic appearance mimics that of a cystic mucocele. (c) Photomicrograph (original magnification, x400; H-E stain) shows monotonous lymphocytic infiltration.
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Figure 23a. Non-Hodgkin lymphoma of the appendix in a 48-year-old woman with acute appendicitis. (a) Axial unenhanced CT scan shows a focal soft-tissue mass in the expected region of the appendix (arrowheads) with stranding of the adjacent fat. (b) Photograph of the cut surface of the gross specimen shows circumferential wall thickening with obliteration of the lumen (arrow). Periappendiceal inflammation and direct lymphomatous extension were seen at histologic analysis.
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Figure 23b. Non-Hodgkin lymphoma of the appendix in a 48-year-old woman with acute appendicitis. (a) Axial unenhanced CT scan shows a focal soft-tissue mass in the expected region of the appendix (arrowheads) with stranding of the adjacent fat. (b) Photograph of the cut surface of the gross specimen shows circumferential wall thickening with obliteration of the lumen (arrow). Periappendiceal inflammation and direct lymphomatous extension were seen at histologic analysis.
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Histologic Features
Typically, appendiceal involvement by non-Hodgkin lymphoma manifests as diffuse circumferential mural infiltration by monotonous-appearing lymphocytes (Fig 22c). In our experience, mantle cell lymphoma and diffuse large B-cell lymphoma are the most common forms (23).
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Other Neoplasms
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Neuroendocrine tumors of the appendix are rare but include ganglioneuromas and paragangliomas (26). Diffuse ganglioneuromatosis has been associated with neurofibromatosis type 1 (27). Mesenchymal tumors of the appendix are rare and are typically benign. Smooth muscle tumors involving the appendix have been reported, with leiomyomas affecting the appendix more often than leiomyosarcomas; the opposite is true for the remainder of the colon (28). Neurofibromas and schwannomas also rarely arise in the appendix (29,30). Recently, however, it has been suggested that gastrointestinal stromal tumors may represent the most common mesenchymal tumor of the appendix (30). It is likely that many of the appendiceal smooth muscle tumors reported in the older literature would be reclassified as gastrointestinal stromal tumors at modern immunohistochemical analysis. Kaposi sarcoma of the appendix has been reported in patients with acquired immunodeficiency syndrome (AIDS) (31). Compared with that of AIDS-related lymphoma, the growth pattern of Kaposi sarcoma is more focal and nodular, but distinguishing between these two entities at imaging may be difficult.
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Conclusions
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Although they are uncommon, primary neoplasms of the appendix often produce clinical symptoms that may lead to imaging evaluation.Asymptomatic tumors may also be detected incidentally at imaging performed for other indications. Recognition of these neoplasms is important for appropriate patient treatment. CT appears to be the modality of choice whenever an appendiceal mass is suggested at physical examination, conventional radiography, contrast enema examination, endoscopy, or US. CT will not only help rule out or confirm an appendiceal tumor, but it may also suggest a more specific diagnosis and help effectively direct therapy.
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Footnotes
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See also the article by Hanbidge et al (pp 663–685)
in this issue.
Abbreviation: AIDS = acquired immunodeficiency syndrome
The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Departments of the Navy, Army, Air Force, or Defense.
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G. Francica, G. Lapiccirella, C. Giardiello, F. Scarano, G. Angelone, F. De Marino, and V. Molese
Giant mucocele of the appendix: clinical and imaging findings in 3 cases.
J. Ultrasound Med.,
May 1, 2006;
25(5):
643 - 648.
[Abstract]
[Full Text]
[PDF]
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M. Kocaoglu and D. P. Frush
Pediatric presacral masses.
RadioGraphics,
May 1, 2006;
26(3):
833 - 857.
[Abstract]
[Full Text]
[PDF]
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M. M. Bittle and F. S. Chew
Radiological Reasoning: Recurrent Right Lower Quadrant Inflammatory Mass
Am. J. Roentgenol.,
September 1, 2005;
185(3_supp):
S188 - S194.
[Abstract]
[Full Text]
[PDF]
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P. J. Pickhardt and S. Bhalla
Primary Neoplasms of Peritoneal and Sub-peritoneal Origin: CT Findings
RadioGraphics,
July 1, 2005;
25(4):
983 - 995.
[Abstract]
[Full Text]
[PDF]
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P. J. Pickhardt
Differential Diagnosis of Polypoid Lesions Seen at CT Colonography (Virtual Colonoscopy)
RadioGraphics,
November 1, 2004;
24(6):
1535 - 1556.
[Abstract]
[Full Text]
[PDF]
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Abstract
LEARNING OBJECTIVES FOR TEST...
