Cysticercosis is considered the most common parasitic disease of the central nervous system. It also affects the eye, skeletal muscle and subcutaneous tissue. The extaocular muscle form is the most common type of orbital cysticercosis. In the ocular form, the favoured sites are the vitreous and subretinal space.1
Human cysticercosis is caused by larval form of swine tapeworm Taenia solium. Man acts as the intermediate host of Taenia solium. Infection occurs on eating raw or inadequately cooked infected pork, consuming food or water contaminated with faecal matter containing ova, or due to autoinfection. The ovum reaches the stomach, develops into an embryo, which makes its way into circulation and lodges into various organs of the body.2
Involvement of the extraocular muscles often mimics orbital pseudotumour. Differentiation between the two is essential for management of the two conditions. On US ocular cysticercosis is seen as a ring-shaped lesion with a central/marginal echogenic nodule representing the scolex. On CT ocular cysticercosis is seen as ring enhancing lesion with pin-head area of increased attenuation representing the scolex. Sometimes the cyst wall may not be seen due to very low attenuation difference between the fluid in the cyst, vitreous and wall of cysticercosis. In the orbit focal thickening of the involved extra-ocular muscle is seen due to an inflammatory reaction. Pathognomonic appearance of the thickened muscle, the cyst and the scolex inside should lead to the diagnosis of cysticercosis.3 The extra-ocular muscle cysts with a visible scolex on CT scan can be treated with oral albendazole along with oral prednisolone. If the scolex is not visible on CT scan or US, an ELISA test may be of diagnostic help. Cystic extra-ocular muscle lesions without a visible scolex are treated with oral corticosteroids; if the cyst persists after treatment, oral albendazole is given.4
Unusual ophthalmic signs and symptoms in the presence of a proptosis especially in endemic country like ours should alert a clinician to the possibility of cysticercosis. Moreover pre- and post-therapy CT provides confirmation to both patients and the treating clinicians.
Dr. Sumer K Sethi’s radiology site http://www.sumerdoc.blogspot.com