Orbital leiomyoma originating from Muller muscle: A case report and review of the literature.

Introduction: Orbital leiomyoma can occur anywhere within the orbit. Posterior tumors arise from vessel wall smooth muscle cells, while anterior tumors develop from the capsulopalpebral or Muller muscle.

Presentation of case: we present a case of a 24-year-old man who was referred for evaluation of chronic right eye swelling involving the medial upper eyelid. Ophthalmologic examination was unremarkable apart from upper lid fullness along with downward and lateral displacement of the globe. MRI revealed a large and well-defined growth in the right medial orbital space. An excisional biopsy was performed which showed a friable mass strongly adherent to the underlying conjunctiva and Muller muscle. This case report has been prepared and reported in line with the SCARE criteria.

Discussion: Orbital leiomyoma usually presents with progressive painless proptosis if situated deep in the orbit. Our patient presented mainly with eyelid fullness and displacement due to the anterior location of his tumor. The diagnosis of orbital leiomyoma has to be confirmed by histopathological and immunohistochemical assessments such as in our case. A literature review was conducted using multiple databases spanning from 1963 to 2023 which concluded male predominance. One similar case to ours has been reported with the tumor originating from supraorbital neurovascular bundle.

Conclusion: To the best of our knowledge, this is the first reported case of an orbital leiomyoma originating from the Muller muscle in the English literature.