From the Archives of the AFIP: Genitourinary Rhabdomyosarcoma in Children

Radiologic-Pathologic Correlation

Abstract Introduction Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

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Radiologic Features

Before the advent of sonography and CT, the presence of a genitourinary tumor was suspected when a pelvic soft-tissue mass was seen on radiographs and when displacement or invasion of normal pelvic structures was observed during intravenous urography, cystography, or barium studies of the gastrointestinal tract (Figure 4, Figure 5). In a review of 56 cases of genitourinary rhabdomyosarcoma collected between 1960 and 1986, intravenous urography was still used in the initial diagnosis of 50% of the cases encountered after 1977 (31). Sonography, CT, and MR imaging have supplanted urography in the evaluation of rhabdomyosarcoma because the soft-tissue mass is directly visualized, local invasion and metastatic spread can be evaluated, and accurate assessment of residual disease after therapy is possible. Nevertheless, the imaging features of the primary tumor are nonspecific in most cases of rhabdomyosarcoma.

Sonography is the screening study of choice in a child with a suspected abdominal or pelvic mass. Sonography often helps define the relationship of the mass to adjacent normal structures (Figure 6), and, on sonograms, a solid tumor is readily distinguished from a hydrocele in a boy who presents with scrotal swelling. The sonographic features of the primary tumor in rhabdomyosarcoma are variable and nonspecific (6,31,33). The solid component of the lesion has been described as hyperechoic or hypoechoic and may contain sonolucent foci (Figure 7, Figure 8) representing hemorrhage or necrosis (32). Sonograms of paratesticular rhabdomyosarcoma demonstrate infiltration of the adjacent testis by tumor (Figure 9), displacement of the adjacent testis without tumor infiltration (Figure 10), or a compressed rim of testicular parenchyma about the tumor (Figure 11). In case reports, color and duplex Doppler sonographic evaluations of paratesticular rhabdomyosarcoma have shown hyperemia and abnormally high diastolic flow within the mass (Figure 7) (34,35). Botryoid rhabdomyosarcoma of the bladder base may appear as a polypoid intraluminal mass resembling a cluster of grapes, a characteristic but not pathognomonic feature.

At CT, rhabdomyosarcoma of the prostate or bladder base is seen as a bulky pelvic mass of heterogeneous attenuation (Figure 3, Figure 12, Figure 13) that may invade the periurethral and perivesical tissues or may extend into the ischiorectal fossa. Calcification is rare (Figure 13) (7). The precise origin of the tumor is often difficult to determine, since primary prostate lesions may invade the bladder base (Figure 3) and the prostate may be invaded by a tumor arising in the bladder. Similarly, vaginal tumors often arise high in the anterior vaginal wall and may be indistinguishable from a primary bladder tumor on imaging studies because of infiltrative growth (Figure 14). In children with genitourinary rhabdomyosarcoma, CT is useful in judging the extent of associated inguinal and retroperitoneal lymph node enlargement (Figure 8) and is the study of choice for the detection of pulmonary metastases (Figure 15) (7).

On MR images of rhabdomyosarcoma, the primary tumor demonstrates nonspecific low signal intensity with T1-weighted pulse sequences and high signal intensity with T2-weighted pulse sequences (Figure 15). Heterogeneous signal intensity representing hemorrhage in various stages of evolution may be identified. In a case report of a 15-year-old boy with prostatic rhabdomyosarcoma, the tumor displayed a low-signal-intensity pseudocapsule that became more conspicuous on T2-weighted images, a finding that was also noted in three other patients with prostatic sarcomas (one with rhabdomyosarcoma, two with leiomyosarcoma) (36). On MR images obtained after intravenous administration of gadopentetate dimeglumine, rhabdomyosarcoma typically enhances heterogeneously (Figure 15, Figure 16). The multiplanar capability of MR imaging permits accurate assessment of local extent of tumor (Figure 15). In one case report, sagittal MR images showed tumor extension into the prevesical space of Retzius in three boys with prostatic rhabdomyosarcoma, a finding not identified prospectively at CT or sonography (37).

Abstract Introduction Clinical Features

Pathologic Features Radiologic Features Differential Diagnosis Treatment and Prognosis

Summary Source Information References