Leiomyoma? Inflammatory myofibroblastic tumour as a mimic

Abstract

Presentation: A 23-year-old female presented with a 7 cm fibroid with atypical features on MRI. There was minimal response to Goserelin (GnRH agonist for sex hormone suppression). The decision was made for hysterectomy. Pathology: Macroscopic examination showed a circumscribed whorled myometrial lesion resembling leiomyoma. Microscopic examination showed a spindle cell lesion predominantly consisting of bland fascicular leiomyoma-like areas and cellular storiform areas. However, the typical thick walled vessels of leiomyoma were notably absent. Other atypical features for leiomyoma included fasciitis-like areas, prominent lymphoplasmacytic infiltrate, and focally infiltrative borders. Immunohistochemistry demonstrated ALK positivity, and FISH studies confirmed ALK rearrangement. The features were of inflammatory myofibroblastic tumour (IMT) of the uterus. Discussion: Uterine IMT is a rare entity with low malignant potential. It may mimic leiomyoma on macroscopic and microscopic examination. The lack of thick walled vessels, fasciitis-like areas, and lymphoplasmacytic infiltrate raised suspicion of an alternative diagnosis to leiomyoma in this case. ALK is positive in the majority of cases thus, low threshold for ALK testing is advised in all uterine lesions that raise morphologic suspicion of IMT.