Primary Splenic Mesothelioma: A Rare Entity

Malignant mesothelioma is a primary neoplasm that arises from the serous membranes lining the pleura, peritoneum, and pericardium. However, mesothelioma arising from the spleen is exceedingly rare and presents unique diagnostic and clinical challenges. A 59-year-old female came with a complaint of a lump in the abdomen and postprandial abdominal distension for one month. The Contrast-Enhanced Computed Tomography (CECT) abdomen showed a large cystic lesion with enhancing solid areas with specs of calcification. The probable diagnosis made radiologically was a splenic cyst or hydatid cyst. Cut-section of the splenectomy specimen had multiple papillary excrescences on the wall and a few areas of haemorrhage. The microscopic sections showed round to epitheloid tumour cells arranged diffusely, in the form of cords and sheets, ill-formed glands and papillary pattern. On Immunohistochemistry, these cells were Cytokeratin (CK), vimentin, Wilms’ tumour suppressor gene1 (WT1) and calretinin positive. However, markers like CK7, CK20, Caudal-type homeobox transcription factor 2 (CDX2), Thyroid Transcription Factor-1 (TTF1), Melan A, Human Melanoma Black 45 (HMB45), CD31, CD34, CD10, Paired Box Gene 8 (PAX8), CD99, Estrogen Receptor (ER) and Epithelial Membrane Antigen (EMA) were negative. Based on both histomorphological and immunohistochemical features, the final diagnosis rendered was epitheloid mesothelioma. Primary malignant mesothelioma of the spleen is a rare entity that should be considered in patients with solitary splenic lesions. Histopathological examination and immunohistochemistry are vital for diagnosis. Complete surgical excision and close follow-up are recommended due to the uncertain prognosis and lack of established treatment guidelines.