Sir,

A 66-year-old Hong Kong Chinese female patient presented with a drooping of her right upper eyelid for 2 weeks. She was born in China and has never travelled abroad. Examination showed a partial ptosis of her right upper lid. It was caused by a palpable, firm, nontender mass with a size of 1 cm in diameter located at the superotemporal region of her right orbit. Ophthalmic examination was otherwise normal. Computed tomography scans of the orbit showed an enlarged lacrimal gland of the right eye associated with a nonenhancing hypodense lesion (Figure 1). No adjacent bony erosion was seen. Serological examinations including eosinophil count were normal. Chest X-ray was unremarkable.

Figure 1
figure 1

Computed tomographic scan showing an enlarged right lacrimal gland associated with a noncontrast-enhancing hypodense lesion.

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An excisional biopsy of the lacrimal gland was performed through lateral orbitotomy. The lacrimal gland was found to be well encapsulated and there was no adhesion to the surrounding structures. Histopathology demonstrated a parasite surrounded by chronic inflammatory cells and significant eosinophils. The presence of thick cuticle, numerous external ridges, two internal longitudinal ridges with lateral chords, heavy musculature and double uterine tubes suggested that the parasite was a female Dirofilaria (Figure 2). The degeneration of the specimen did not allow further differentiation into subspecies. After the surgery, the eyelid contour returned to normal and there was no recurrence at the last follow-up visit of 1 year.

Figure 2
figure 2

Haematoxylin and eosin stain. Solid arrow: multiple transverse sections of a single female Dirofilaria in the lacrimal gland. Empty arrow: lacrimal gland capsule.

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Dirofilariasis is a parasitic infection of domestic and wild animals, but it occasionally affects human as zoonotic disease. D. repens is the most frequently reported subspecies outside United States.1 Mosquitoes are the biological vectors in transmitting the parasite from animals to human. Sometimes they can penetrate the tissue and spread systemically into internal organs.2 Pampiglione et al3 reported a case series of dirofilarial infections in which 30% had ocular involvement. Ocular infection can be subconjunctival, periorbital, orbital, or intraocular. Orbital infections can result in proptosis, ptosis, or diplopia.4

Systemic features such as fever, lymphadenopathy, and reactive arthritis are occasionally seen. Only 25% of subcutaneous cases has peripheral eosinophilia.4 The diagnosis is made on the basis of histological and morphological identification. Serology and molecular biology techniques may provide supportive information, but the significance of them being the definitive diagnostic tool has not yet been established.3, 5

In our case, the acquisition of the parasite may have occurred in Hong Kong or in China. Neither the time of transmission nor the route of entry into the lacrimal gland can be determined. Direct inoculation into lacrimal gland is probably not possible. One possibility is that, following an innocuous mosquito bite in the periorbital region, the microfilaria developed in the subcutaneous tissue and finally burrowed into the lacrimal gland. Surgical excision is the recommended treatment for dirofilariasis and this can also provide histological diagnosis. Unlike other filarial infections such as onchocerciasis and loiasis, microfilaraemia is unusual and antihelminthic agents are generally not indicated.

To the best of our knowledge, this is the only report in the English literature that dirofilariasis presented as a lacrimal mass. The initial clinical and radiological findings were all suggestive of a benign tumour. The deceptive feature led to a diagnostic challenge. One should consider this as an unusual differential diagnosis especially for those who have travelled in the past to endemic areas.