Epididymal rhabdomyosarcoma is an exceptionally rare mesenchymal tumor, and its occurrence in young adults is an even rarer phenomenon. Typically, this aggressive malignancy primarily afflicts children and adolescents, often presenting as a painless scrotal mass. The scarcity of documented cases in young adults underscores the significance of reporting and analyzing such instances to expand our understanding of this malignancy.

We present the case of an 18-year-old patient who presented with a painless scrotal mass that had been progressively evolving over a three-month period. Upon examination, the mass measured 2 × 2 cm, was firm, non-tender, and palpable separately from the testis. Clinical examinations of lymph nodes and the abdomen yielded normal findings. Subsequently, routine abdomen and pelvis imaging, along with scrotal sonography, indicated the presence of an encapsulated mass on the left side, situated outside the testis, displaying vascularity within but devoid of calcifications [Fig.1]. This presentation raised suspicion of an adenomatoid tumor of the epididymis or leiomyoma.

Serum alpha-fetoprotein (AFP) levels were found to be 2.5 ng/mL, and beta-human chorionic gonadotropin (HCG) levels were less than 0.13 ng/mL, both within normal ranges. The patient then underwent excision of the para-testicular mass, and histopathological analysis confirmed the diagnosis of spindle cell rhabdomyosarcoma [Fig.2]. Immunohistochemistry further revealed that the tumor cells were diffusely positive for desmin, myogenin, and MYOD1, while being negative for AE1/AE3 and CD31 [Fig.3-7]. Subsequently, a left high inguinal orchidectomy was performed, along with excision of the scrotal scar. Histopathological examination revealed a vaguely nodular area near the lower pole of the testis, which displayed residual neoplasm composed of fusiform, elongated/spindle to ovoid cells arranged haphazardly, indicative of sclerosing rhabdomyosarcoma.

The patient received a total of 23 cycles of radiotherapy coupled with 12 cycles of chemotherapy, following a regimen that included Vincristine (2 mg/m²), Dactinomycin (1.6 mg/m²), and Cyclophosphamide (3 gm/m²). Each chemotherapy session was completed within a single day, with a 21-day cycle interval.

Rhabdomyosarcoma usually occurs in the extremities. A para-testicular localization is rare; the tumor develops from mesenchymal tissues of the spermatic cord, and epididymis [1]. There are two frequency peaks found for the development of rhabdomyosarcoma, the first at the age of 4 years and the second at the age of 18 years, as in our case. There is no predilection for race [2]. Primary tumors of the epididymis and spermatic cord are very rare. Differential diagnoses include testicular torsion, epididymoorchitis, scrotal abscess and, rarely testicular tuberculosis. Embryonal rhabdomyosarcoma is the most frequent malignant tumor of the spermatic cord in children and young adults, but it may also occur in the testis, epididymis and testicular tunica. These tumors tend to spread via the lymphatic system to iliac lymph nodes; nevertheless, spread via the blood stream to the liver and lungs do occur. The clinical presentation of our patient, an 18-year-old male, with a progressively evolving painless scrotal mass, is consistent with reported cases of epididymal rhabdomyosarcoma. The firm, non-tender nature of the mass, separate from the testis, is a characteristic feature often seen in such cases. Synchronous or metachronous involvement of the pelvic lymph nodes. Embryonal rhabdomyosarcoma may occasionally show small groups of anaplastic cells with bizarre nuclei that seem to be associated with a more aggressive clinical course. Recently, a new histologic appearance termed spindle cell rhabdomyosarcoma has been identified in patients with low stage paratesticular primaries. Other variants of rhabdomyosarcoma are alveolar, orphic and pleomorphic.

Epididymal rhabdomyosarcoma remains a rare and diagnostically challenging entity, especially when presenting in young adults. This case underscores the importance of considering this malignancy in the differential diagnosis of scrotal masses, even among older age groups, to ensure early detection and appropriate management.

Contributors: AI, IM: manuscript writing, patient management; HM, RV, AS: manuscript editing, patient management; MP, AR, JM: critical inputs into the manuscript. AI will act as a study guarantor. All authors approved the final version of this manuscript and are responsible for all aspects of this study.

Funding: None; Competing interests: None stated.