Congenital Rapidly Progressive Perianal Embryonal Rhabdomyosarcoma With Spindle Cell Morphology: A Rare Presentation

Area of Science:

• Pediatric Oncology
• Surgical Pathology
• Medical Imaging

Background:

• Rhabdomyosarcoma is a rare soft tissue sarcoma in children.
• Perianal rhabdomyosarcoma is exceptionally uncommon, representing about 2% of all rhabdomyosarcoma cases.
• Embryonal rhabdomyosarcoma with spindle cell morphology (ERMS) is a specific subtype with distinct features.

Purpose of the Study:

• To report a rare case of ERMS presenting as a perianal mass in a neonate.
• To emphasize the diagnostic challenges and the importance of immunohistochemistry in unusual tumor locations.
• To highlight the clinical presentation and imaging findings of pediatric perianal tumors.

Main Methods:

• Case presentation of a 2-day-old infant with a progressive perianal swelling.
• Abdominal MRI to characterize the soft tissue mass.
• Histopathological examination including immunohistochemical analysis (desmin, MYOD1, myogenin, MKI67).

Main Results:

• A 4.7 × 2.7 × 2.5 cm heterogeneous soft tissue mass was identified in the perineum extending into the pelvis.
• Histopathology revealed spindle and round cells with striations.
• Immunohistochemistry confirmed ERMS with diffuse desmin and MYOD1 positivity, focal myogenin positivity, and a 30% MKI67 proliferation index.

Conclusions:

• Perianal ERMS is a rare entity requiring high suspicion.
• Immunohistochemical markers are essential for accurate diagnosis of ERMS, especially in atypical locations.
• Multimodality imaging and pathology are critical for effective management of pediatric soft tissue tumors.