Retrobulbar hydatid cyst in the horse.

This study involves a case of a horse suffering from an exophthalmic (protruding) and blind eye resulting from a retrobulbar hydatid cyst, a rare space-occupying lesion at the back of the eyeball.

Case History

• The subject of the case study is a five-year-old bay Welsh Cob mare, which was bought by its owner four months prior.
• At the time of purchase, the owner suspected that the horse was already blind in one eye, and in the following months, the horse developed slow-growing periorbital swelling (swelling around the eye socket).
• Upon examination, the afflicted eye was found to be exophthalmic (protruding from the eye socket), skewed downwards, and exhibited marked chemosis (swelling) in the lower eyelid. There was also significant swelling in the upper orbital region.
• The horse’s eye was partially closed and exhibited signs of a mucopurulent (containing mucus and pus) ocular discharge.
• Upon ophthalmoscopic examination, the optic nerve was found to be totally atrophied (wasted away) with no visible retinal blood vessels, pointing to blindness in the affected eye.
• The presence of a retrobulbar mass exerting pressure on the optic nerve was inferred.

Treatment

• Given the irreversible blindness and presumed presence of a likely tumorous mass, enucleation (removal of the eye) was suggested.
• During the routine enucleation, a moderately hard mass was found near the optic nerve. Attempts to remove the mass led to the burst of the lesion, revealing a cystic lining and marking its identification as a hydatid cyst.
• The subsequent removal of the cystic tissue was followed by standard closure and healing procedures.
• Post-operative treatment included intramuscular penicillin for six days. The swelling around the eye started to subside after three days and was completely resolved after two weeks.
• The removal of the cystic mass also resulted in a notable improvement in the horse’s temperament.

Pathology

• The excised cyst, optic nerve, and portions of muscle and connective tissue were biochemically processed and embedded in paraffin wax for histological examination.
• Upon examining the stained sections, the cyst was found to feature a laminated, acellular wall with blood cells and cellular debris lining its internal surface. This aligned with the histological characteristics of a hydatid cyst.