Extragastrointestinal Gastrointestinal Stromal Tumor Presenting as Paratesticular Mass - A Diagnostic Conundrum.

Extragastrointestinal gastrointestinal stromal tumors are uncommon in the paratesticular region and pose a diagnostic challenge. A 47-year-old man presented with a painless testicular mass for three months. Ultrasonography showed a solid lesion in the right distal spermatic cord region. Excision of the mass showed an encapsulated solid, firm tumor of size 5 cm. Microscopic examination showed a spindle cell tumor arranged in fascicles, nodular and storiform patterns. The mitotic rate was 17-19/5 mm². The mesothelial lining of the tunica vaginalis was noted. Using immunohistochemistry, the tumor cells were positive for KIT, DOG1, and CD34, while negative for SMA, desmin, S100, STAT6, and EMA. H3K27me3 was retained in the tumor cells. The MIB-1 labeling index was 25% in the area of greatest labeling. We report an additional example of paratesticular EGIST and discuss the diagnostic approach and literature review. Knowledge about this tumor at rare sites and the clinicopathological features are needed for the definitive diagnosis and prognosis.