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Congenital Extrarenal Extra-Central Nervous System Malignant Rhabdoid Tumor of the Upper Extremity: A Case Report.

Malignant rhabdoid tumor (MRT) is an extremely rare and highly aggressive tumor that occurs in infancy or childhood1. MRT was first described as a rhabdomyosarcomatoid variant of Wilms tumor because of its histologic resemblance to rhabdomyoblasts and its most frequent presenting location as a renal tumor2,3. Since then, MRT has also been found in the central nervous system (CNS), ileum, lung, heart, liver, skin, and intestines4-7. We present a rare case of congenital extrarenal extra-CNS MRT of the forearm in an infant with an aggressive course and poor outcome. The patient’s parents were informed that data concerning the case would be submitted for publication, and they provided consent.

A four-month-old otherwise well baby girl had presented shortly after birth with a 0.5-cm area of bluish discoloration over the volar aspect of the left forearm. This discoloration had remained stable until three months of age, when this area began to rapidly enlarge and become more discolored. Ultrasound revealed a large heterogeneous soft-tissue mass in the forearm with areas of cystic change consistent with an infantile hemangioma versus sarcoma. Computed tomography (CT) of the chest showed left axillary lymphadenopathy.

The patient underwent CT-guided needle biopsy of the lesion, which measured 7.8 cm × 3.4 cm. Histologic evaluation and immunohistochemical studies of the biopsy were demonstrative of a high-grade sarcoma, consistent with MRT (Figs. 1-A through 1-D⇓). Fluorescent in situ hybridization (FISH) was performed. Because it was negative for the Ewing sarcoma breakpoint region, the break-apart FISH ruled out Ewing and desmoplastic small round cell tumor; because it was negative for the FKHR gene, the break-apart FISH ruled out alveolar rhabdomyosarcoma. Karyotyping for the chromosomal t(X;18) translocation was negative, thus ruling out synovial sarcoma. Subsequent staging evaluation included bilateral bone marrow aspirate …