Benign Granular Cell Tumor Masquerading as Thyroid Eye Disease

Introduction: Granular cell tumor (GCT) is a benign neoplasm of Schwann cell origin that occasionally arises within the periocular tissues. Tumors have been reported in the lacrimal sac, eyelid, caruncle, orbicularis muscle, orbit, extraocular muscles, conjunctiva, anterior uvea, and ciliary body. While rectus muscle involvement with associated diplopia has been reported in several cases, imaging typically reveals a discrete mass emanating from the muscle of origin. We present an unusual case of GCT with fusiform inferior rectus muscle enlargement masquerading as thyroid eye disease (TED), managed using a multidisciplinary surgical approach.

Methods: Case report.

Results: A 48-year-old female with a history of hyperthyroidism presented with two years of vertical diplopia. Exam revealed hyperglobus, proptosis, and lid retraction of the left eye (OS), with diminished supraduction (−3.5/4) and infraduction (−2/4). Orbital MRI demonstrated fusiform enlargement of the inferior rectus with tendinous sparing, and signal isointense to normal muscle on T1 and heterogeneously hyperintense on T2 (Fig. 1). Also noted by the interpreting radiologist were mild medial rectus enlargement and proliferation of postseptal fat. The patient was diagnosed with TED. During attempted strabismus surgery, a firm, homogenous, yellow-white mass was discovered diffusely infiltrating the inferior rectus, including its anterior insertion. The planned muscle recession was therefore aborted and a muscle biopsy performed. Pathologic analysis revealed abnormal connective tissue composed of large polygonal cells with disorganized, granular, eosinophilic cytoplasm. The nuclei appeared dark, mildly pleomorphic, and distorted. No high-grade cytologic features or necrosis were evident to suggest malignancy. Cells were positive for S-100 and CD-68 and negative for AE1/AE3, CD45, melan-A, desmin, and caldesmon. Given these features, a diagnosis of benign granular cell tumor was made. The patient subsequently underwent combined tumor resection with the oculoplastics and otolaryngology services. Trans-conjunctival orbitotomy with orbital floor decompression was performed and the tumor was transected at the anterior insertion. It was subsequently depressed into the maxillary sinus, sectioned at the orbital apex, and delivered via a Caldwell-Luc antrostomy. The orbital floor was reconstructed with a porous polyethylene/titanium implant, which was later removed due to episodic inflammation. Biopsy at this time demonstrated no evidence of tumor recurrence/progression. Despite the absence of an inferior rectus muscle, the patient is close to orthophoric in primary gaze awaiting consideration of strabismus surgery.

Conclusion: In this case, history and imaging initially suggested a diagnosis of TED, which draws attention to the previously unrecognized possibility of GCT masquerading as an orbital inflammatory disorder. It also highlights a novel interdisciplinary strategy for surgical management of large orbital GCTs, with only one prior report of trans-sinus resection.

Fig. 1 Orbital MRI demonstrated fusiform enlargement of the inferior rectus with tendinous sparing, and signal isointense to normal muscle on T1 and heterogeneously hyperintense on T2.

No conflict of interest has been declared by the author(s).