(Radiographics. 2000;20:S53-S66.)
© RSNA, 2000
CT of Unusual Iliopsoas Compartment Lesions1
Malai Muttarak, MD and
Wilfred C. G. Peh, FRCP, FRCR
1 From the Department of Radiology, Chiang Mai University, Chiang Mai, Thailand (M.M.); and the Department of Diagnostic Radiology, Singapore General Hospital, Outram Rd, Singapore 169608 (W.C.G.P.). Recipient of a Certificate of Merit award for a scientific exhibit at the 1999 RSNA scientific assembly. Received February 2, 2000; revision requested March 9; revision received April 24; accepted April 26. Address correspondence to W.C.G.P. (e-mail: gdrpcg@sgh.gov.sg).
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Abstract
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The authors reviewed the anatomy of the iliopsoas compartment and a spectrum of unusual lesions affecting structures in this compartment, with emphasis on the role of computed tomography (CT). Lesions in the iliopsoas compartment are caused by acute infection, tumor, or hemorrhage. The knowledge of detailed clinical data can help improve the diagnostic accuracy, particularly with regard to primary iliopsoas lesions. CT is useful for delineating the source of secondary iliopsoas lesions, guiding biopsy, and performing follow-up of treated lesions. Nonenhanced CT can help detect fresh hemorrhage, fat-containing tumor, and calcification, whereas contrast materialenhanced CT optimizes imaging of infection, tumor, and aneurysm.
Index Terms: Muscles, abnormalities, 40.656 • Muscles, CT, 40.1211 • Muscles, iliopsoas • Muscles, infection, 40.2012, 40.2025, 40.23, 40.29 • Muscles, neoplasms, 40.39
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Introduction
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The iliopsoas muscle compartment can be involved by many different disease processes, including infection, tumor, and hemorrhage. Patients may present with a wide variety of symptoms that are often nonspecific, resulting in a delay in diagnosis. Direct psoas muscle extension from infective spondylitis, either of pyogenic or tuberculous origin, is probably best recognized (1–5). The availability of advanced imaging techniques, particularly computed tomography (CT), has enabled diseases affecting the iliopsoas compartment to be detected with increasing clarity. This facilitates early diagnosis and appropriate treatment (6–10).
We performed this study to review the normal anatomy of the iliopsoas compartment and the imaging features of a variety of unusual iliopsoas compartment lesions, with emphasis on the role of CT.
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Anatomy
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The iliopsoas compartment consists of the psoas major, psoas minor, and iliacus muscles. The psoas major muscle arises from the transverse processes of the 12th thoracic and lumbar vertebrae and the adjacent tendinous arches. It merges with the iliacus muscle at the level of the L5 through S2 vertebrae to form the iliopsoas muscle. This composite muscle passes beneath the inguinal ligament, and its tendon inserts on the lesser trochanter of the femur (6,8,9). The psoas minor muscle originates from the bodies of the T12 and L1 vertebrae and inserts on the iliopectineal eminence of the innominate bone and the iliac fascia. This muscle is absent in 40% of individuals (6). The iliacus muscle arises from the iliac wing and merges with the psoas major to form the iliopsoas muscle and tendon (Fig 1).
The muscles in this compartment act as flexors of the thigh and trunk and as lateral flexors of the lower vertebral column. Superiorly, the psoas muscle passes beneath the arcuate ligament of the diaphragm; therefore, it is a potential channel for communication between the mediastinum and the upper thigh. All muscles in the iliopsoas compartment are covered by the iliopsoas fascia. The psoas muscle is in contact with the posterior renal fascia at and superior to the level of the renal hilus (Fig 2a). Inferior to the renal hilus level, however, the psoas muscle is in direct contact with fat surrounding the kidney, as the posterior renal fascia fuses with the fascia of the lateral psoas margin, the quadratus lumborum, or both (Fig 2b). Further inferiorly, the posterior renal fascia courses medially to rejoin the psoas fascia, giving rise to a potential communication between the iliopsoas compartment and the posterior pararenal space (Fig 2c). Because the anterior and posterior renal fascia are not always fused inferiorly, this potential opening offers a pathway for the spread of disease.
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Figure 2a. Diagrams illustrate cross-sectional anatomy of the left psoas compartment at the level of the upper renal pole (a), at the level of the lower renal pole (b), and inferior to the level of the lower renal pole (c). A = aorta; C = descending colon; LK(L) = left kidney, lower pole; LK(U) = left kidney, upper pole; PS = psoas muscle; QL = quadratus lumborum; U = ureter.
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Figure 2b. Diagrams illustrate cross-sectional anatomy of the left psoas compartment at the level of the upper renal pole (a), at the level of the lower renal pole (b), and inferior to the level of the lower renal pole (c). A = aorta; C = descending colon; LK(L) = left kidney, lower pole; LK(U) = left kidney, upper pole; PS = psoas muscle; QL = quadratus lumborum; U = ureter.
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Figure 2c. Diagrams illustrate cross-sectional anatomy of the left psoas compartment at the level of the upper renal pole (a), at the level of the lower renal pole (b), and inferior to the level of the lower renal pole (c). A = aorta; C = descending colon; LK(L) = left kidney, lower pole; LK(U) = left kidney, upper pole; PS = psoas muscle; QL = quadratus lumborum; U = ureter.
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Anteriorly, the psoas muscle is closely related to the pancreas, aorta, inferior vena cava, and retroperitoneal lymph nodes. Structures such as the duodenum, cecum, and appendix in the right side of the abdomen and the descending colon in the left side of the abdomen are close to the iliopsoas compartment. Violation of the retroperitoneal fascial planes by infective, hemorrhagic, and neoplastic processes may give rise to lesions within this compartment. The iliopsoas compartment often acts as a conduit for the distant spread of disease, which may actually dominate the initiating process. An understanding of this complex anatomy is important for the accurate diagnosis of lesions affecting the psoas muscle.
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Materials and Classification
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We retrospectively analyzed the clinical records and images obtained in 43 patients (21 male and 22 female patients; age range, 6–89 years; mean age, 45.8 years) with unusual iliopsoas lesions (excluding those due to infective spondylitis). All 43 patients underwent CT, and six also underwent magnetic resonance (MR) imaging. The final diagnosis was established in all patients by means of pathologic examination or clinical follow-up. The iliopsoas lesions were classified according to origin and whether the disease process was primary (affecting only the iliopsoas compartment) or secondary (extending into the iliopsoas compartment from an adjacent structure) (Table).
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Infection
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The iliopsoas muscle was primarily involved by infection in five patients and secondarily involved in 12 patients (Table). Primary iliopsoas abscesses are rare and are usually idiopathic (1,4–6,8). The most common organisms are Staphylococcus aureus and mixed gram-negative organisms. Immunocompromised patients, especially those receiving corticosteroids and chemotherapy, and patients with the human immunodeficiency virus (HIV) are predisposed to primary iliopsoas infection by opportunistic organisms (8,11) (Fig 3). Secondary infection of the iliopsoas muscle is much more frequent and may spread from infections of the bowel (eg, appendicitis, diverticulitis, Crohn disease, perforated colonic carcinoma) (Fig 4), kidney (eg, perinephric abscesses) (Fig 5), and bone (eg, osteomyelitis) (Fig 6).
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Figure 3a. Primary iliopsoas infection in a 54-year-old HIV-positive male drug addict. Contrast-enhanced CT scans obtained at different levels show an extensive abscess (*) within the grossly enlarged right psoas compartment. There is prominent rim enhancement within small loculated areas of infection located in the right paraspinal muscles. Focal pockets of gas bubbles (arrows in b) are present. Drainage was performed, and S aureus was cultured.
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Figure 3b. Primary iliopsoas infection in a 54-year-old HIV-positive male drug addict. Contrast-enhanced CT scans obtained at different levels show an extensive abscess (*) within the grossly enlarged right psoas compartment. There is prominent rim enhancement within small loculated areas of infection located in the right paraspinal muscles. Focal pockets of gas bubbles (arrows in b) are present. Drainage was performed, and S aureus was cultured.
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Figure 3c. Primary iliopsoas infection in a 54-year-old HIV-positive male drug addict. Contrast-enhanced CT scans obtained at different levels show an extensive abscess (*) within the grossly enlarged right psoas compartment. There is prominent rim enhancement within small loculated areas of infection located in the right paraspinal muscles. Focal pockets of gas bubbles (arrows in b) are present. Drainage was performed, and S aureus was cultured.
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Figure 4. Secondary iliopsoas infection in a 66-year-old man with ruptured appendicitis. Contrast-enhanced CT scan shows a large mass involving the right iliopsoas muscle. It has rim enhancement and a prominent air-fluid level (arrow).
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Figure 5a. Secondary iliopsoas infection in a 26-year-old woman with known left chronic pyelonephritis. Contrast-enhanced CT scans obtained at different levels show a large renal calculus (thin arrow in a) and extension of perinephric infection into the left iliopsoas and paravertebral muscles (thick arrows). Scale is in centimeters.
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Figure 5b. Secondary iliopsoas infection in a 26-year-old woman with known left chronic pyelonephritis. Contrast-enhanced CT scans obtained at different levels show a large renal calculus (thin arrow in a) and extension of perinephric infection into the left iliopsoas and paravertebral muscles (thick arrows). Scale is in centimeters.
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Figure 6a. Secondary iliopsoas infection in a 47-year-old woman with right iliac osteomyelitis. (a, b) Initial contrast-enhanced CT scans obtained at different levels show a large mass within the right iliacus muscle with a prominent air-fluid level (arrow in a) and destruction of bone (arrow in b). Drainage was performed, and Salmonella enteritidis was cultured. (c) Follow-up CT scan obtained 15 months later shows complete resolution of the right iliacus abscess.
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Figure 6b. Secondary iliopsoas infection in a 47-year-old woman with right iliac osteomyelitis. (a, b) Initial contrast-enhanced CT scans obtained at different levels show a large mass within the right iliacus muscle with a prominent air-fluid level (arrow in a) and destruction of bone (arrow in b). Drainage was performed, and Salmonella enteritidis was cultured. (c) Follow-up CT scan obtained 15 months later shows complete resolution of the right iliacus abscess.
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Figure 6c. Secondary iliopsoas infection in a 47-year-old woman with right iliac osteomyelitis. (a, b) Initial contrast-enhanced CT scans obtained at different levels show a large mass within the right iliacus muscle with a prominent air-fluid level (arrow in a) and destruction of bone (arrow in b). Drainage was performed, and Salmonella enteritidis was cultured. (c) Follow-up CT scan obtained 15 months later shows complete resolution of the right iliacus abscess.
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On CT scans, an abscess may manifest as enlargement of the iliopsoas muscle by a low-attenuation lesion. The lesion typically displays rim enhancement after the intravenous administration of contrast material (3–5,9–13) (Fig 7). This enhancement pattern is seen at both CT and MR imaging (10). Abscesses appear as areas of low signal intensity at nonenhanced T1-weighted MR imaging and as areas of high signal intensity at nonenhanced T2-weighted MR imaging. These findings are nonspecific and are indistinguishable from those of metastases and lymphoma (14). Secondary findings include obliteration of the surrounding fascial planes, bone destruction, and gas bubbles.
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Figure 7. Typical rim enhancement of a primary iliopsoas abscess in a 19-year-old man with HIV infection. Contrast-enhanced CT scan shows gross enlargement of the right psoas muscle with prominent rim and septal enhancement. Some extension into the right paraspinal muscle is also present.
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In their series, Lenchik et al (15) report that a low-attenuation lesion was the most reliable CT feature of iliopsoas abscess. This finding is nonspecific, however, because it is also seen in necrotic neoplasms and chronic hematomas (6,8,9,12). Although gas bubbles, which are suggestive of infection (2,5,8,9,12), are rarely seen in tumor and hemorrhage, they have been described in both these conditions (9,15,16). CT is more sensitive than MR imaging for demonstrating gas bubbles (11,17). CT-guided aspiration and drainage may be needed to help confirm the diagnosis and guide disease management. CT is also useful in the follow-up of treated lesions (5,11,12) (Fig 8).
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Figure 8a. Follow-up of treated secondary iliopsoas infection in a 10-year-old boy who had undergone appendectomy. (a, b) Initial CT scans obtained at different levels show a right iliac fossa abscess involving the right psoas muscle. The abscess was drained, and S aureus was cultured. (c, d) Follow-up CT scans obtained 2 months later at different levels show complete resolution of the abscess.
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Figure 8b. Follow-up of treated secondary iliopsoas infection in a 10-year-old boy who had undergone appendectomy. (a, b) Initial CT scans obtained at different levels show a right iliac fossa abscess involving the right psoas muscle. The abscess was drained, and S aureus was cultured. (c, d) Follow-up CT scans obtained 2 months later at different levels show complete resolution of the abscess.
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Figure 8c. Follow-up of treated secondary iliopsoas infection in a 10-year-old boy who had undergone appendectomy. (a, b) Initial CT scans obtained at different levels show a right iliac fossa abscess involving the right psoas muscle. The abscess was drained, and S aureus was cultured. (c, d) Follow-up CT scans obtained 2 months later at different levels show complete resolution of the abscess.
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Figure 8d. Follow-up of treated secondary iliopsoas infection in a 10-year-old boy who had undergone appendectomy. (a, b) Initial CT scans obtained at different levels show a right iliac fossa abscess involving the right psoas muscle. The abscess was drained, and S aureus was cultured. (c, d) Follow-up CT scans obtained 2 months later at different levels show complete resolution of the abscess.
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For both primary and secondary iliopsoas infections, the clinical history and knowledge of the laboratory signs of infection are important clues to diagnosis. For secondary lesions, the adjacent structure should be carefully examined to delineate the source and pathway of the spread of infection. In infected kidneys, pyonephrosis and obstructing calculi are frequently encountered (Fig 9).
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Figure 9a. Images demonstrate the source and pathway of secondary iliopsoas infection in a 44-year-old man with replacement lipomatosis of the left kidney. (a, b) Contrast-enhanced CT scans obtained at different levels show a large renal calculus (arrowheads in a), extensive perirenal fat (arrows in a), and pyonephrosis (arrows in b), which resulted in a left psoas abscess (*). Scale is in centimeters.
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Figure 9b. Images demonstrate the source and pathway of secondary iliopsoas infection in a 44-year-old man with replacement lipomatosis of the left kidney. (a, b) Contrast-enhanced CT scans obtained at different levels show a large renal calculus (arrowheads in a), extensive perirenal fat (arrows in a), and pyonephrosis (arrows in b), which resulted in a left psoas abscess (*). Scale is in centimeters.
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Tumor
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In our series, the iliopsoas compartment was primarily involved by tumor in four patients and secondarily involved in 10 (Table). Primary intrinsic tumors of the iliopsoas muscles are rare. The iliopsoas muscle may be affected by primary tumors such as liposarcoma, fibrosarcoma, leiomyosarcoma, and hemangiopericytoma (8,9,18). Hematogenous spread of malignancies directly to the iliopsoas muscle is exceedingly rare. The most common types of primary malignancies that metastasize to the iliopsoas muscle are lymphoma, melanoma, and carcinoma originating from the cervix, ovary, stomach, lung, and breast (2,9,12,14,16,18) (Fig 10).
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Figure 10. Primary iliopsoas involvement by tumor in a 46-year-old woman with carcinoma of the cervix. Contrast-enhanced CT scan shows a heterogeneous necrotic tumor in the left psoas muscle.
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Tumor involvement of the iliopsoas muscle is most often secondary to direct extension of an adjacent tumor. These include retroperitoneal, abdominal, or pelvic tumors (Fig 11); neurogenic tumors (Fig 12); direct invasion from adjacent lymph nodes; bone tumors (Figs 13, 14); and local tumor recurrence. Unfortunately, it is often impossible to differentiate among tumor, abscess, and hematoma on the basis of CT appearances alone. Imaging features include enlargement of the muscle, areas of low attenuation, irregular margins, bone destruction, and retroperitoneal lymphadenopathy (6,15,18). Feldberg et al (8) suggest that, compared with abscess and hematoma, tumors are more likely to obliterate adjacent fascial planes. Lenchik et al (15), however, found that fascial disruption was also common in abscess and hematoma.
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Figure 11. Secondary iliopsoas involvement by tumor in a 61-year-old man with malignant mesenchymoma of the retroperitoneum. Contrast-enhanced CT scan shows a large tumor, containing small areas of fatty density, invading the left psoas muscle.
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Figure 12a. Secondary iliopsoas involvement by tumor in a 57-year-old woman with neurogenic tumor. Contrast-enhanced CT scans obtained at different levels show a well-defined hypoattenuating mass arising from the widened left S1 foramen (arrowheads in b). The mass displaces and compresses the left psoas muscle (arrow). Scale is in centimeters.
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Figure 12b. Secondary iliopsoas involvement by tumor in a 57-year-old woman with neurogenic tumor. Contrast-enhanced CT scans obtained at different levels show a well-defined hypoattenuating mass arising from the widened left S1 foramen (arrowheads in b). The mass displaces and compresses the left psoas muscle (arrow). Scale is in centimeters.
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Figure 13. Secondary iliopsoas involvement by tumor in a 55-year-old man with hepatocellular carcinoma. Contrast-enhanced CT scan shows metastatic osteolytic destruction of the L1 vertebra with enhancing soft-tissue extension into the right psoas muscle.
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Figure 14a. Secondary iliopsoas involvement by tumor in a 72-year-old man with lymphoma of the L5 vertebra. Axial (a) and coronal (b) contrast-enhanced spin-echo T1-weighted MR images (repetition time msec/echo time msec = 580/20) show that the tumor has a large, heterogeneous, soft-tissue component (arrows) that invades both psoas muscles and abuts the aorta and inferior vena cava.
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Figure 14b. Secondary iliopsoas involvement by tumor in a 72-year-old man with lymphoma of the L5 vertebra. Axial (a) and coronal (b) contrast-enhanced spin-echo T1-weighted MR images (repetition time msec/echo time msec = 580/20) show that the tumor has a large, heterogeneous, soft-tissue component (arrows) that invades both psoas muscles and abuts the aorta and inferior vena cava.
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The MR imaging features of iliopsoas lesions have been previously reported (10,14,17,19), but the results are also nonspecific. Iliopsoas metastases have low signal intensity on nonenhanced T1-weighted images and abnormally high signal intensity on T2-weighted images (17,19). Other features include psoas enlargement and replacement, reticulated texture, and peritumoral edema (20,21). MR imaging, however, allows images to be obtained in a variety of different planes, produces increased tumor conspicuity, and has no ionizing radiation hazard. Because imaging appearances are nonspecific, knowledge of the history of a known preexisting tumor is useful. Imaging-guided biopsy may be needed to make the diagnosis (Fig 15). Both CT and MR imaging are useful for monitoring previously treated tumors (Figs 16, 17).
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Figure 15a. Imaging-guided biopsy of an iliopsoas compartment tumor in a 48-year-old man with multiple schwannomas. (a) CT scan obtained with the patient in a prone position shows the biopsy needle in the well-defined mass. (b) CT scan obtained after biopsy shows blood products, which produced a fluid-fluid level (arrow in b), within the tumor. The left psoas muscle (arrowheads in a and b) is splayed and compressed by the tumor.
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Figure 15b. Imaging-guided biopsy of an iliopsoas compartment tumor in a 48-year-old man with multiple schwannomas. (a) CT scan obtained with the patient in a prone position shows the biopsy needle in the well-defined mass. (b) CT scan obtained after biopsy shows blood products, which produced a fluid-fluid level (arrow in b), within the tumor. The left psoas muscle (arrowheads in a and b) is splayed and compressed by the tumor.
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Figure 16a. Primary iliopsoas involvement by metastatic tumor in a 46-year-old man with pelvic leiomyosarcoma. (a, b) Initial contrast-enhanced CT scans obtained at different levels 1 year after excision of a primary pelvic leiomyosarcoma do not reveal an iliopsoas lesion. (c, d) Follow-up contrast-enhanced CT scans obtained at different levels 2 years later show two metastatic deposits in the upper and lower right psoas muscles. There was no recurrence in the pelvis.
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Figure 16b. Primary iliopsoas involvement by metastatic tumor in a 46-year-old man with pelvic leiomyosarcoma. (a, b) Initial contrast-enhanced CT scans obtained at different levels 1 year after excision of a primary pelvic leiomyosarcoma do not reveal an iliopsoas lesion. (c, d) Follow-up contrast-enhanced CT scans obtained at different levels 2 years later show two metastatic deposits in the upper and lower right psoas muscles. There was no recurrence in the pelvis.
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Figure 16c. Primary iliopsoas involvement by metastatic tumor in a 46-year-old man with pelvic leiomyosarcoma. (a, b) Initial contrast-enhanced CT scans obtained at different levels 1 year after excision of a primary pelvic leiomyosarcoma do not reveal an iliopsoas lesion. (c, d) Follow-up contrast-enhanced CT scans obtained at different levels 2 years later show two metastatic deposits in the upper and lower right psoas muscles. There was no recurrence in the pelvis.
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Figure 16d. Primary iliopsoas involvement by metastatic tumor in a 46-year-old man with pelvic leiomyosarcoma. (a, b) Initial contrast-enhanced CT scans obtained at different levels 1 year after excision of a primary pelvic leiomyosarcoma do not reveal an iliopsoas lesion. (c, d) Follow-up contrast-enhanced CT scans obtained at different levels 2 years later show two metastatic deposits in the upper and lower right psoas muscles. There was no recurrence in the pelvis.
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Figure 17a. Treatment monitoring of an iliopsoas compartment tumor in a 42-year-old woman with carcinoma of the cervix. (a) Initial contrast-enhanced CT scan shows heterogeneous enlargement of the right iliopsoas muscle owing to metastasis. (b) Follow-up contrast-enhanced CT scan obtained 1 month later, after chemotherapy, shows further progression of the right iliopsoas muscle metastasis to involve the adjacent bones (arrowheads). (c) Coronal spin-echo T1-weighted MR image (560/11) shows the craniocaudal extent of the right iliopsoas metastasis. Scale is in centimeters.
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Figure 17b. Treatment monitoring of an iliopsoas compartment tumor in a 42-year-old woman with carcinoma of the cervix. (a) Initial contrast-enhanced CT scan shows heterogeneous enlargement of the right iliopsoas muscle owing to metastasis. (b) Follow-up contrast-enhanced CT scan obtained 1 month later, after chemotherapy, shows further progression of the right iliopsoas muscle metastasis to involve the adjacent bones (arrowheads). (c) Coronal spin-echo T1-weighted MR image (560/11) shows the craniocaudal extent of the right iliopsoas metastasis. Scale is in centimeters.
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Figure 17c. Treatment monitoring of an iliopsoas compartment tumor in a 42-year-old woman with carcinoma of the cervix. (a) Initial contrast-enhanced CT scan shows heterogeneous enlargement of the right iliopsoas muscle owing to metastasis. (b) Follow-up contrast-enhanced CT scan obtained 1 month later, after chemotherapy, shows further progression of the right iliopsoas muscle metastasis to involve the adjacent bones (arrowheads). (c) Coronal spin-echo T1-weighted MR image (560/11) shows the craniocaudal extent of the right iliopsoas metastasis. Scale is in centimeters.
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Hemorrhage
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In our series, the iliopsoas compartment was primarily involved by hemorrhage in three patients and secondarily involved in nine patients (Table). Hemorrhage confined within the iliopsoas compartment may be caused by a bleeding diathesis or anticoagulant therapy or it may be spontaneous (Fig 18). Hemorrhage may occur secondary to trauma, tumor, recent surgery or biopsy, and extension from adjacent bleeding organs and vessels (8,9,12,22).
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Figure 18. Primary iliopsoas hemorrhage in a 29-year-old man with hemophilia who had spontaneous hemorrhage. Nonenhanced CT scan shows a discrete mass of high attenuation, representing fresh hemorrhage, within the right psoas muscle.
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On CT scans, fresh hemorrhage is seen as a discrete mass of high attenuation (Fig 19). A fluid-fluid level may be present owing to the hematocrit effect. Chronic hematomas may be hard to distinguish from abscesses and tumors, and percutaneous aspiration may be necessary to differentiate between them (12,15). If a mass lesion is seen in the adjacent renal area, the presence of intratumoral fat may be suggestive of a renal angiomyolipoma (22) (Fig 20). Intravenous administration of contrast material is useful for delineating ruptured vascular lesions (Fig 21). The MR imaging appearance of hemorrhage depends on the age of the hematoma (17,19). Subacute hematomas may obscure the iliopsoas muscle with a characteristic high signal intensity on nonenhanced T1-weighted images. Chronic hemorrhage produces areas of low signal intensity on both nonenhanced T1- and T2-weighted images owing to hemosiderin deposition (14).
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Figure 19. Hyperattenuating appearance of fresh primary iliopsoas hemorrhage in a 75-year-old woman with aplastic anemia and spontaneous hemorrhage. Nonenhanced CT scan shows a large fresh hematoma causing enlargement of the left psoas muscle.
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Figure 20a. Secondary iliopsoas involvement by hemorrhage in a 29-year-old woman with lymphangioleiomyomatosis and spontaneous rupture of a right renal angiomyolipoma. The patient had previously undergone left lung transplantation. Nonenhanced CT scans of the kidneys obtained at different levels show areas of fatty attenuation within the angiomyolipoma (arrowheads in a) in the upper pole of the right kidney. High-attenuation areas of fresh hemorrhage (arrowheads in b) involve the right psoas muscle. The white box in a is a region-of-interest marker used to measure the degree of attenuation (of fat in this case).
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Figure 20b. Secondary iliopsoas involvement by hemorrhage in a 29-year-old woman with lymphangioleiomyomatosis and spontaneous rupture of a right renal angiomyolipoma. The patient had previously undergone left lung transplantation. Nonenhanced CT scans of the kidneys obtained at different levels show areas of fatty attenuation within the angiomyolipoma (arrowheads in a) in the upper pole of the right kidney. High-attenuation areas of fresh hemorrhage (arrowheads in b) involve the right psoas muscle. The white box in a is a region-of-interest marker used to measure the degree of attenuation (of fat in this case).
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Figure 21a. Images demonstrate the usefulness of intravenous contrast material in a 71-year-old woman with secondary iliopsoas involvement by hemorrhage due to rupture of an abdominal aortic aneurysm. Nonenhanced (a) and contrast-enhanced (b) CT scans show areas of fresh hemorrhage, seen as patchy areas of high attenuation, in the false aneurysm that has extended into the right psoas muscle. The aneurysm lumen (arrows) is clearly seen in b.
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Figure 21b. Images demonstrate the usefulness of intravenous contrast material in a 71-year-old woman with secondary iliopsoas involvement by hemorrhage due to rupture of an abdominal aortic aneurysm. Nonenhanced (a) and contrast-enhanced (b) CT scans show areas of fresh hemorrhage, seen as patchy areas of high attenuation, in the false aneurysm that has extended into the right psoas muscle. The aneurysm lumen (arrows) is clearly seen in b.
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Because the CT characteristics alone are not reliable enough to differentiate among hematoma, abscess, and tumor, knowledge of the relevant clinical history is important when making the accurate diagnosis. Imaging is useful, however, for determining the underlying causes of hemorrhage and for directing management. Subsequent intervention can be tailored according to the lesion type and anticipated risk of repeat hemorrhage (Fig 22).
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Figure 22a. Secondary iliopsoas involvement by hemorrhage in a 34-year-old woman who had spontaneous rupture of a right renal angiomyolipoma. (a, b) Nonenhanced CT scans obtained at different levels show pockets of fat within a small angiomyolipoma in the upper pole of the right kidney. A large perinephric hematoma (arrows in b) extends into the right psoas muscle. Because the vascular pedicle was not involved, nephron-preserving surgery was possible. (c) Follow-up CT scan shows complete tumor excision.
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Figure 22b. Secondary iliopsoas involvement by hemorrhage in a 34-year-old woman who had spontaneous rupture of a right renal angiomyolipoma. (a, b) Nonenhanced CT scans obtained at different levels show pockets of fat within a small angiomyolipoma in the upper pole of the right kidney. A large perinephric hematoma (arrows in b) extends into the right psoas muscle. Because the vascular pedicle was not involved, nephron-preserving surgery was possible. (c) Follow-up CT scan shows complete tumor excision.
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Figure 22c. Secondary iliopsoas involvement by hemorrhage in a 34-year-old woman who had spontaneous rupture of a right renal angiomyolipoma. (a, b) Nonenhanced CT scans obtained at different levels show pockets of fat within a small angiomyolipoma in the upper pole of the right kidney. A large perinephric hematoma (arrows in b) extends into the right psoas muscle. Because the vascular pedicle was not involved, nephron-preserving surgery was possible. (c) Follow-up CT scan shows complete tumor excision.
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Conclusions
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CT provides a noninvasive way of visualizing the presence and extent of diseases involving the iliopsoas compartment. MR imaging is a helpful adjunct to CT and should be used selectively. The imaging features of infection, tumor, and hemorrhage in the iliopsoas compartment may be similar. Accurate diagnosis can be achieved with a thorough understanding of the iliopsoas compartment anatomy and its relationship to the adjacent organs combined with details of the clinical data and imaging features. In equivocal cases, CT can be used to guide biopsy and drainage procedures.
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Footnotes
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Abbreviation: HIV = human immunodeficiency virus
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References
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Abstract
Introduction
