Primary Intra-Orbital Hydatid Cyst: A Case Report of a Rare Cause of Exophthalmos

Background

Hydatid cyst is a zoonotic infection caused by the tapeworm Echinococcus granulosus.¹ It is endemic to Africa, Asia, Australia, and Mediterranean countries.² Dogs are the definitive hosts for the parasite while sheep and cattle serve as intermediate hosts.³ Humans are accidental intermediate hosts affected by the tapeworm after ingesting viable eggs. During its life cycle in the human body, the tapeworm commonly affects the liver and lungs.⁴ Rarely, echinococcosis may involve the orbit and patients may present with proptosis, decreased vision, and ocular pain.^2,4–6 Here, we present a case of a 60-year-old woman who presented with left eye proptosis secondary to a primary orbital hydatid cyst. To the best of the author’s knowledge, this is the first reported case of orbital hydatid disease from Ethiopia.

Case Presentation

A 60-year-old female sheep herder from Eritrea presented to St. Paul’s Hospital Millennium Medical College ophthalmology department with a 3-month history of painless left eye protrusion associated with progressive decreased vision of the left eye. Otherwise, she had an unremarkable history. Visual acuity in the right eye was 6/18 and counting finger in front of the eye on the left eye. Physical examination revealed a 4 mm discrepancy on exophthalmometry between the two eyes with a proptosis of 21 mm on the left eye. On fundus examination, there was a tortuous temporal arcade and grade 4 papilledema in the left eye. Otherwise, there was an unremarkable finding. Laboratory investigation revealed a normal complete blood count. Computerized tomography (CT) of the brain and orbit showed a well-defined thin-walled non-enhancing fluid density cystic mass in the left orbital cavity measuring 2.6 cm by 2.0 cm by 1.9 cm with compression and lateral displacement of the globe as well as compression and stretching of the optic nerve (Figure 1A–C). The left medial rectus muscle was not clearly and separately visualized from the lesion. There were no osseous lytic or sclerotic changes of the bony orbit. The CT scan was suggestive of a hydatid cyst of the orbit. Abdominal ultrasound and chest X-ray findings were unremarkable.

Figure 1 Computerized tomography (CT) of the brain and orbit with (A) Axial view, (B) Coronal view, and (C) Sagittal view respectively.

The patient was given albendazole 400mg orally twice per day for 2 weeks and re-evaluated. Subsequently, she was taken to the operating room with an impression of a left medial mass secondary to Hydatid cyst. The cyst was approached through a medial anterior orbitotomy. Intraoperatively, a cystic mass attached to the inferior aspect of the medial rectus (MR) was identified. The cyst ruptured during manipulation and a clear fluid came out. A paper white cyst lining was removed in piecemeal and the external capsule was excised with care not to severely damage the MR muscle. Then, the surgical field was irrigated with 3% hydrogen peroxide solution followed by copious normal saline solution, and the tissue was sent for histopathological examination. Biopsy result revealed an acellular laminated membrane with germinal epithelium and a daughter cyst with protoscolices (Figure 2A and B) and surrounding soft tissue consisting of chronic inflammatory cells confirming the diagnosis of hydatid cyst. Cytology from cyst fluid showed a hemorrhagic background with no cells.

Figure 2 A slide showing acellular laminated membrane with germinal epithelium (A) and a daughter cyst with protoscolices (B).

On her first postoperative day, she had lid edema with limited adduction of the left eye and mild ocular pain. Oral albendazole 400mg twice daily was continued postoperatively. Follow-up on her 7th post-operative day showed that there was mild improvement in the adduction deficit and lid swelling had resolved. Subsequent follow-up on her 21st postoperative day showed left eye visual acuity of counting fingers at two meters and the adduction deficit improved to −2. Furthermore, the optic disc edema also resolved to grade 1. However, the patient moved back to Eritrea, and we were not able to follow the subsequent progress of the patient beyond the first 3 weeks.

Discussion

Orbital hydatid disease is a very rare parasitic infection caused by the tapeworm Echinococcus granulosus.⁷ Similar to other zoonotic disease affecting humans, accidental ingestion of ova passed by the definitive hosts, canines, is the route of entry to the human body.^8,9 Hydatid disease mainly affects the liver and the lung but it can rarely affect other organs including the orbit and the central nervous system.^7,10 Previous studies have shown that orbital hydatid disease accounts for only 1% of the hydatid disease burden.¹¹ Close contact with animals such as dogs, sheep, and cattle is a risk factor for acquiring the infection which was also identified in our patient.¹²

The clinical manifestation of hydatid disease is primarily related to the mass effect exerted by the cyst on adjacent structures.⁷ The mass effect is more pronounced in structures with limited space like the orbit.¹ Patients with orbital hydatid cyst commonly present with a longstanding unilateral proptosis of the eye similar to our patient.¹¹ Other manifestations include decreased vision due to longstanding compression of the optic nerve, ocular pain, limitation of ocular motility, and chemosis.^1,12

Patients with suspected hydatid disease of the orbit should be thoroughly investigated. Complete blood count, serum antibody test, and imaging studies are crucial to exclude other potential differential diagnoses. Mass lesions such as dermoid cyst, epidermoid cyst, hemangiomas, post-traumatic hematomas, and mucocele can be considered differentials based on the presenting symptom.¹³ CT scan and MRI are the preferred choices of imaging and can help the clinician narrow the differential prior to surgery.^1,6 However, histopathology remains the definitive diagnostic modality.¹

Management of orbital hydatid disease includes a 2 to 4 week course of anthelmintic drugs, preferably albendazole, followed by surgical excision of the cyst.^6,13 Preoperative anthelmintic treatment is vital to prevent parasite seeding and anaphylactic reactions in case the cyst ruptures during manipulation while performing surgery.^8,13 If intraoperative rupture of cyst occurs, irrigation with hypertonic saline and hydrogen peroxide would kill daughter cysts and prevent further spread.¹⁴ The operating surgeon should aim for complete excision of the cyst with minimal ocular tissue damage.¹¹

Conclusion

Echinococcosis, although extremely rare, has the potential to affect the eye. It should be kept in the list of differential diagnoses for patients with pertinent history and risk factors. Early recognition and treatment of orbital echinococcosis is crucial to prevent vision-related complications.