Colonic epithelioid leiomyoma with chondroid differentiation: A potential diagnostic pitfall and the first case of a novel type of colonic leiomyoma

Abstract

Colonic leiomyomas are relatively common lesions discovered incidentally during colonoscopy, particularly in the distal sigmoid colon and rectum. The classic histologic appearance of colonic leiomyomas are well-circumscribed lesions that arise from the muscularis mucosae and occupy the submucosa. They are composed of well-differentiated smooth muscle cells that are spindled with cigar-shaped nuclei and abundant eosinophilic cytoplasm. Traditionally, leiomyomas stain positively for markers of smooth muscle differentiation, such as desmin and smooth muscle actin. Herein, we describe a case of a 53-year-old woman with an incidentally discovered colon polyp that revealed epithelioid cells within a chondroid-type matrix, with ERG and smooth muscle actin expression. To our knowledge, this is the first case of an epithelioid leiomyoma of the colon with chondroid differentiation described in the literature. We describe the unique morphologic and immunohistochemical properties of this lesion and we highlight the potential diagnostic pitfalls that may be encountered during the work-up of this entity.

Keywords

• Colon polyp
• Epithelioid leiomyoma
• ERG
• Chondroid