T. Shafi Khan ( Department of Surgery, Aga Khan University Hospital, Karachi. )
Asim Khan ( Department of Surgery, Aga Khan University Hospital, Karachi. )
Pilomatrix carcinoma is a skin tumour about which there is a relative paucity of material in the plastic surgical literature. In the course of their practice most plastic surgeons will have come across the benign skin lesion designated "Clacifying Epithelioma o Malherbe" named thus in recognition of Malherbe\\\'s description of the entity in I 880, even though erroneously ascribed the tissue of origin to be the sebaceous gland’. Forbis and Helwig in 1961 reviewed 228 such tumours, demonstrated the tissue of origin to be the hair matrix and proposed the term “pilomatrixoma” as more representative of the lesion 2. These are rare benign skin neoplasms with an incidence rate that varies from 1 in 924 dermatopathologic specimens to I in 2200 surgical pathologic specimens. They are slow growing, typically stony hard dermal nodules, usually less than 3 cm. in size and are most commonly found on the head and neck. They tend to occur in children and teenagers, with a slight female preponderance Taffe et al 3 and more recently Kaddu et al4 have however documented a second peak of onset in the middle aged and elderly. Radiological examination classically shows a solitary, sharply demarcated subcutaneous tumour with extensive sandlike or dense calcification5 Histologically they are composed of nests of basaloid cells which undergo abrupt keratinization forming ghost or shadow cells in a background of inflammatory ce Is and calcification6. The recommended treatment is excision which is usually a simple matter as the lesion is well circumscribed. Recurrence is rare 2 but has been documented. Though the term ‘giant calcifying epithel ioma” had been coined7 to denote a tumour that behaved aggressively and recurred, it was not until 1980 when Lopansri and M ihrn flrst used the term “pi lomatrix carcinoma” to describe a recurrent lesion with certain distinctive histological features8. Since then there have been occasional reports in the literature but it remains a rare tumour with less than 30 cases reported till 1994 4.
In keeping with the rarity of the carcinomatous lesion reports in the literature are few. In the largest review of pilomatrix carcinoma to date totaling 20 such cases, Sau et al. reported that the tumours varied in size from 1—10 cm. in size and occurred more often in middle-aged men with a predilection for the posterior neck and back10. Follow-up of 17 patients revealed a local recurrence in 10 (59%) and multiple recurrences in 3 patients. As early as 1927 Gromiko reproted a case of calcifying epithelioma with three recurrences which ultimately necessitated amputation of the right arm11. Though the biologic potcntial of pilomatrix carcinoma is similar to basal cell carcinoma, as it is a locally invasive lesion that does not metastasize, yet there have beeii reports of pulmonary metastases12 and multiple visceral metastases leading to a fatal outcome13.
The importance of the above is to highlight that not all tumours of hair matrix origin follow an innocent course. Add to it is the fact that it can at times be difficult to clinically distinguish a pilomatrix lesion in the adult from a variety of skin lesions like a sebaceous cyst, fibrohistiocytic proliferations, basal cell carcinoma, keratoacanthoma and cutaneous metastases 4. Histologically the distinction between pilomatrixoma and pilornatrix carcinoma can be difficult and an erroneous diagnosis of the much common pilomatrixoma can be made. Flow cytometric DNA content analysis reveals no significant difference between pilomatrixoma and pilomatrix carcinoma 14. After extensive review of the microscopic slides of their own and other cases which exhibited aggressive behaviour, Lopnasri and Mihm 8 advised caution in interpreting tumours with extensive basaloid proliferation and rnitoses.
They put forward two microscopic features which, in their opinion, should denote pilomatrix carcinoma:
1) Active proliferating hyperchromatic vesicular basaloid cells with numerous rnitoses.
ii) Infiltration into fat lobules and/or into underlying structures.
In summary awareness of the malignant potential of certain skin tumours of hair matrix origin is important in preventing the untoward sequelae of inadequately managed pilomatrix carcinoma. Where there is the slightest doubt the lesion should he subjected to early wide excision and close monitoring thereafter.
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