Paratesticular rhabdomyosarcoma

Clinical History

An 8 year old boy was referred to the urological department with a painless swelling of the right scrotum. There was no fever. Physical examination revealed a palpable mass and a fluid collection in the right scrotum. There were no palpable inguinal lymph nodes.

Imaging Findings

Ultrasound examination confirmed the presence of a solid multilobular mass adjacent to the right testis floating in a hydrocele. The echotexture of the mass was slightly heterogenous and almost isoechoic compared to the testis. Colour Doppler ultrasound showed marked hypervascularity of the mass. Intra-operative frozen section during explorative surgery revealed a rhabdomyosarcoma, and a total inguinal orchidectomy was performed. Histology of the resected specimen showed loose myxoid foci containing primitive cells and regions of dense spindle cells. Scattered mitoses were present. The tumour was positive for desmin, an immunohistochemical marker of myogenic differentiation. Cytogenetic evaluation showed up to 5 copies of chromosome 13; polysomy of chromosome 13 is a frequent feature of embryonal rhabdomyosarcoma. Staging chest and abdominal computed tomography (CT) showed no distant metastases. Adjuvant chemotherapy was initiated.

Discussion

The term rhabdomyosarcoma in fact refers to a mesenchymal tumour originating from striated muscle, though rhabdomyosarcoma typically arises in regions lacking striated muscle. Genitourinary rhabdomyosarcoma is second in frequency after rhabdomyosarcoma of the head and neck area, and is the most common tumour of the lower genitourinary tract in children. It may originate in the urinary bladder, prostate, testes and extratesticular tissues, penis, perineum, vagina and uterus. As the exact site of origin may be difficult to determine for primary scrotal rhabdomyosarcomas, the term paratesticular rhabdomyosarcoma is more appropriate. Paratesticular rhabdomyosarcoma has a bimodal age distribution, with one peak during infancy and the other during adolescence. Presenting symptom most often is a unilateral painless scrotal swelling. Ultrasound (and MR imaging) findings are nonspecific, and care must be taken because similar findings may be seen in more common paratesticular tumors such as fibromas, leiomyomas, and adenomatoid tumors. The sonographic appearance varies from predominately solid to almost cystic with solid mural nodules, reflecting the gross pathologic appearance of a solid mass with occasional cystic degeneration and haemorrhage. The tumour may be ill defined with infiltrative margins or well circumscribed by tunica vaginalis or tunica albuginea. They may envelop or frankly invade the epididymis and testis. Colour-Doppler ultrasound shows increased low resistance flow. The most common subtype in the paratesticular region is embryonal carcinoma, followed by alveolar, pleomorphic, and mixed. Paratesticular rhabdomyosarcomas most frequently spread to retroperitoneal lymph nodes. Inguinal lymphadenopathy may be present if tumour invasion of the scrotal skin has occurred. The lungs and bone are the most frequent affected distant metastatic sites. Radical orchiectomy with combined chemotherapy is the standard treatment which results in excellent outcome in patients with localized disease. Lymphadenectomy is indicated in cases were CT suggests involvement of retroperitoneal nodes, and the retroperitoneum should be assessed surgically in cases with suspicious radiological lymph nodes.

Differential Diagnosis List

Final Diagnosis

Paratesticular rhabdomyosarcoma, embryonal subtype.

URL:	https://www.eurorad.org/case/7369
DOI:	10.1594/EURORAD/CASE.7369
ISSN:	1563-4086