Solitary Fibrous Tumor of the Umbilical Region in a Pediatric Patient.

Fibrous tumors are rare tumors of mesenchymal origin arising in the serosal surfaces within the body. Although commonly seen in adults, solitary fibrous tumors rarely occur in children. Histopathology and immunohistochemistry are the methods of choice for diagnosing solitary fibrous tumors. A 2-year-old male presented with a swelling over the umbilicus for the prior 8 months. The umbilical mass was excised and sent for histopathologic examination. The skin-covered greyish soft tissue mass measured 6 × 5.5 × 4.5 cm, and the cut surface showed a homogenous greyish growth. On microscopic examination, a predominantly well-circumscribed encapsulated tumor was noted, with spindle shaped cells arranged in a haphazard manner and ectatic vascular channels. The cells were immunoreactive for CD34 and signal transducer and activator of transcription 6 (STAT6) and negative for smooth muscle actin, desmin, myogenin, MyoD1, CD99, epithelial membrane antigen, and beta-catenin. The aim of this case is to make clinicians aware of the umbilicus as a rare site of solitary fibrous tumor in children and the diagnostic importance of STAT6.