Germ Cell Tumor Presenting as a Mesenteric Cyst: a Case Report and Literature Review.

Mesenteric cysts, typically benign and asymptomatic, are incidental findings during abdominal investigations for nonspecific symptoms. Their origin is commonly in the mesentery of the small bowel, mesocolon, or retroperitoneum. This paper reports a rare case of a 22-year-old male with a mesenteric cyst presenting as a right lower abdominal mass. Ultrasonography revealed a heterogenous collection, leading to surgical excision. Histopathology unexpectedly revealed an extragonadal yolk sac tumor (YST) originating in the mesentery, a rarity often misdiagnosed as a cyst. YST, primarily found in gonads, is infrequently reported extragonadally. This study contributes to the limited literature on primary peritoneal YST, discussing clinicopathological parameters and presenting a detailed case. The pathogenesis of extragonadal germ cell tumors, including YST, remains debated, with migration and stagnation of germ cells during embryonic development proposed as a prevalent theory. Histopathological examination of extragonadal YST mirrors gonadal YST, featuring various patterns. Immunohistochemistry, crucial for diagnosis, reveals positive expression for SALL-4, glypican-3, PLAP, AFP, and panCK. SALL-4 emerges as the most sensitive marker for extragonadal YST. This case underscores the importance of accurate postoperative histopathology and immunohistochemistry in distinguishing mesenteric YST from cysts, as misdiagnosis can impact prognosis. The rarity of extragonadal YST emphasizes the need for comprehensive understanding and recognition in clinical practice. The study contributes valuable insights into diagnosis and management, shedding light on a challenging aspect of surgical pathology.