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Editor,—Pilomatrixoma (also called benign calcifying epithelioma of Malherbe) is a rare, benign tumour originating from the matrix of the hair root, first described in 1880 by Malherbe and Chenantais.1 Pilomatrixoma can occur almost anywhere on the body but has a propensity to occur in the head and neck region, often involving the eyelid or eyebrow.2It is most commonly seen in children and adolescents with a female predominance reported.2 3 Pilomatrixoma is often misdiagnosed clinically and the correct diagnosis only established after excision and histological examination.3
This case report describes an unusual presentation of pilomatrixoma of the lower eyelid following trauma. It also highlights some characteristic features of this tumour that can help the clinician differentiate it from other eyelid masses found in children.
A 4 year old girl presented to the eye casualty department with a lump on her left lower eyelid. She had been hit by a ball 3 months previously after which the lump had appeared. On examination, it measured 1 cm by 1 cm, had a red-blue discoloration, and was hard and painful to touch. Her ocular examination was otherwise normal.
An initial diagnosis of unresolving haematoma or possible cholesterol granuloma was made. She was listed for surgical exploration of the lump but before this could be carried out she re-presented because the lump had grown rapidly in size. It now measured 2 cm by 2.2 cm and still had the red-blue discoloration (Fig 1).
Excision biopsy was expedited. The skin-orbicularis muscle incision was made over the mass, inferior to the lateral aspect of the lower lid, and the tumour shelled out intact. The tumour was well circumscribed, nobbly hard, of yellowish white colour, and measuring 19 mm × 15 mm × 8 mm (Fig 2A and B).
Histopathology showed a pseudoencapsulated mass composed mainly of eosinophilic acellular material in which ghost cells were prominent, together with numerous small foreign body giant cell granulomata and considerable calcification. At the periphery there were focal areas of basaloid cells with little cytoplasm. Squamous maturation of these cells to form keratinous material was present (Fig 2C and D). The pathological diagnosis was pilomatrixoma.
The child has made an uneventful recovery and remains free of tumour 2 years later.
Pilomatrixoma typically presents as a firm, non-tender, subcutaneous nodule, adherent to the skin but not fixed to underlying tissue.4 In our case the lump was tender with bruising caused by preceding trauma. The association with trauma is unusual.
In their survey of 150 cases of pilomatrixoma in a paediatric hospital Orlando and coworkers found no history of trauma or inflammation.5 However, a lesion that bruised easily on trauma has been described in a case report of an aggressive variant of pilomatrixoma that grew over the parotid area in the face of a 4 year old boy.6
Red-blue or blue discoloration of the skin is a more typical feature of pilomatrixoma7 8 and should help to differentiate it from inclusion and dermoid cysts which the are most common misdiagnoses.9 Inclusion cysts have a diffuse yellow colour when filled with keratin and are more likely to be softer and more fluctuant than pilomatrixoma. They are also rarer in children than in adults. The skin over dermoid cysts looks normal and can be moved freely over the lesions.
Capillary haemangiomas that arise in the subcutaneous tissue without involving the skin can have a blue-purple colour similar to pilomatrixoma but that lesion tends to be soft and compressible on palpation and growth is much faster than pilomatrixoma. A chalazion can become inflamed but does not show the red-blue discoloration of pilomatrixoma.
Rhabdomyosarcoma is the most common orbital malignancy of childhood that can present rarely as an eyelid mass with erythema of the overlying skin but no other symptoms.10 However, the tumour usually extends to the deeper orbital tissues and is not restricted to the subcutaneous tissues.
Pilomatrixoma of the eyelid is often misdiagnosed clinically. But there are characteristic features of the lesion that can help clinicians differentiate it from other tumours seen in children. The tumour is usually rock-hard, freely mobile within the subcutaneous tissue, but lightly attached to the overlying skin which can have a blue or red-blue discoloration. The tumour may also present following trauma, as demonstrated by this case.