Trichilemmal cyst of the bulbar conjunctiva: a rare presentation.

We report a rare case of trichilemmal cyst involving the bulbar conjunctiva. A 55-year-old female presented with a history of a painless, progressive swelling in the left bulbar conjunctiva adjacent to the nasal limbus of 3 years duration. Wide excision biopsy was performed. Histopathologic examination findings were consistent with those of trichilemmal cyst. Trichilemmal cyst should be considered as differential diagnosis in a case of limbal nodule.

INTRODUCTION

Atrichilemmal cyst also known as pilar cyst is a common cyst that forms from a hair follicle.[1] The cysts are smooth filled with keratin, a protein component found in hair, nails, and skin. Occasionally, trichilemmal cysts can become malignant.

To the best of our knowledge, trichilemmal cysts involving the bulbar conjunctiva have not been reported so far. We report a rare case of trichilemmal cyst involving the bulbar conjunctiva.

CASE REPORT

A 55-year-old female from South India of Dravidian race presented with a history of gradually progressive, painless swelling in the left bulbar conjunctiva adjacent to the nasal limbus of 3 years duration. It was not associated with redness, discharge or blurring of vision. There was no history of trauma or history of any surgery performed in the past. There was no significant family history. On clinical examination, there was a nodular mass adjacent to the nasal limbus of left eye measuring 5 mm × 5 mm, fixed to the underlying tissue, non-tender, lying within the pterygium [Figures 1a and b]. The transillumination test was negative. Examination of the rest of the anterior and posterior segment was unremarkable. The right eye was unremarkable. A fold of subconjunctival tissue extending from the swelling to the caruncle was observed during wide excision biopsy of the lesion. The specimen was sent for histopathological examination.

Figure 1

(a and b) Nodular mass at the limbus

Histopathology indicated the presence of sebaceous material.

Microscopic examination showed a cyst lined by stratified squamous epithelium with the absence of granular cell layer, focal basal cell hyperplasia, and flakes of keratin within the cyst [Figures 2a–c]. A diagnosis of a conjunctival trichilemmal cyst was made based on the histopathological findings.

Figure 2a

Histopathology of the lesion from Figure 1. Cyst cavity filled with keratin lacking a granular cell layer in its wall (H and E, ×400)

Figure 2c

Absence of granular cell layer in the cyst wall

Focal Basal cell hyperplasia in the cyst wall

DISCUSSION

A limbal nodule often presents a difficult clinical, histopathologic, and therapeutic challenge.[2] It poses a diagnostic challenge because most lesions are transitions between inflammation, inflammatory hypertrophies, and true neoplasms.[3]

A trichilemmal cyst, also known as wen, pilar cyst or isthmus-catagen cyst forms from a hair follicle.[4] Though most often found on the scalp, they can also occur on other parts of the body such as the upper lip, palpebral conjunctiva, caruncle, and pulp of the index finger.[567] The rare location of bulbar conjunctiva in this case could be explained as originating from the caruncle and being pushed toward the nasal limbus. These cysts are similar to epidermal cysts, both being keratinous cysts. However histologically trichilemmal cysts lack a granular cell layer.[4] Approximately, 20% of the epithelial cysts are trichilemmal cysts and other 80% are epidermoid.[8]

Very rarely, trichilemmal cysts can undergo malignant transformation.[910] In our case, the cyst showed basal cell hyperplasia without cell atypia or mitosis. There are a few reported cases of trichilemmal cyst and malignant trichilemmal tumor of the eyelid.[111213] However to the best of our knowledge, no cases of trichilemmal cysts involving the bulbar conjunctiva have been reported. This case report highlights the need for considering trichilemmal cyst as differential diagnosis of the limbal nodule.