Solitary adult orbital myofibroma: A case Report
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Myofibromas are uncommon but important tumors that can occur in the head and neck region, including the orbit. Seen more often in children, they can rarely be encountered in adult patients. Diagnosis is possible with a panel of immunostains and molecular analysis can be further confirmatory. A 24-year-old woman presented as a referral for magnetic resonance imaging. She initially presented to her primary care provider for a 6-month history of a swollen left eyelid and pressure behind her eye. On examination, her visual acuity was 20/20 without correction and intraocular pressure was 20 mmHg, bilaterally. She was noted to have a slightly proptotic and inferiorly displaced left eye. Exophthalmometer measured the right eye at 13 mm and the left eye at 15 mm. Visual fields and extraocular movements were full and intact. No afferent pupillary defect was noted. The remainder of the anterior segment exam for both eyes was normal.

On dilated exam, the vitreous was clear. Optic nerves were normal in size and slightly asymmetric, with a right cup-to-disc ratio of 0.3 and a left cup-to-disc ratio of 0.2. The right macula was flat. The retinal vessels appeared normal in the right eye and were slightly congested in the left eye. The remainder of the retinal exam was within normal limits bilaterally. Optical coherence tomography (OCT) demonstrated a horizontal fold in the left macula. MR imaging showed an enhancing, well defined, solid, extraconal orbital mass in the left orbit. The patient subsequently underwent a left lateral orbitotomy and excisional biopsy of the mass. Pathology of the left eye tumor revealed a spindle cell neoplasm composed of cells with plump oval nuclei and scant cytoplasm arranged in short, haphazard fascicles. There was a rich vascular network throughout the tumor with numerous thin-walled, branched, and staghorn-like vessels. There was a concentric perivascular arrangement of tumor cells around larger vessels that exhibited more abundant lightly eosinophilic cytoplasm.

On immunohistochemistry, the spindle cells showed diffuse cytoplasmic positivity for desmin and were negative for CD34, STAT6 and myogenin. TLE1 was positive in rare tumor cells and endothelial cells. CD34 highlighted the vasculature within tumor, and SMA was positive in vessel walls and spindle cells. Molecular analysis was performed utilizing DNA and RNA based next-generation sequencing with an expanded cancer mutation profiling assay that evaluated for the presence of substitutions, insertion/deletions and gene fusions in a large panel of genes, and for copy number alterations in a subset of them, both inclusive of PDGFRB.The morphologic and immunohistochemical features were most consistent with a diagnosis of myofibroma/myopericytoma.