Giant omental fibromatosis presenting as pelvic mass

Omental fibromatosis (abdominal desmoids) is a rare benign but locally aggressive neoplasm characterized by mass like or infiltrative growth of fibrous tissue. It usually arises from the abdominal wall or the extremities, however rarely it may also arise in the omentum, ileocolic mesentery, transverse or sigmoid mesocolon and ligamentum teres. Here, we present an 18-year-old male, who presented with lower abdominal pain and palpable lump in hypogastric region. Computed tomography of the abdomen showed large heterogeneous mass in lower abdomen, possibly arising from mesentery with regional adenopathy. Patient underwent exploratory laparotomy with a preoperative diagnosis of mesenteric tumour possibly gastrointestinal stromal tumour (GIST). Histopathological examination revealed the lesion as omental fibromatosis. To the best of our knowledge, very few cases of omental fibromatosis are noted in literature. Here, we describe a rare case of giant omental fibromatosis which resembled mesenteric GIST clinically but finally diagnosed as fibromatosis by histomorphology and immunohistochemistry (IHC). The present article describes fibromatosis of greater omentum and the difficulty in preoperative diagnosis, as it is frequently misdiagnosed as GIST.