Isolated Orbital Cysticercosis Involving the Superior Oblique Muscle

Cysticercosis is a parasitic infection caused by the larval forms of Taenia solium. Humans acquire the disease by ingestion of the eggs or the larvae. The larvae then enter the blood stream and affects systemic organs like the brain and the striated muscles. Ocular involvement can be either intraocular (anterior and posterior chamber) or of the orbital adnexae (extra-ocular muscles, subconjunctival space, optic nerve, and lacrimal glands). The superior rectus muscle is most commonly involved. Diagnosis of orbital adnexal cysticercosis requires high clinical index of suspicion. Ultrasound of the orbit can demonstrate the scolex within the hypoanechoic cystic lesion. CT shows a hypodense lesion with a hyperdense scolex, and detects calcification. MRI offers better characterization of the lesion. It is hyperintense on fluid sensitive sequences with a hypointense scolex on thin sections. T2 and FLAIR shows adjacent inflammatory changes. Enhancement depends on the stage of infection. Differentials include pseudotumor (not cystic and lacks scolex, involves tendinous insertion) and metastasis (known primary). Adnexal lesions are treated medically, while surgery is reserved for residual lesions and intra-ocular, subconjunctival and eyelid lesions.