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Pilomatricoma, also known as pilomatrixoma or calcifying epithelioma of Malherbe, is a benign skin tumor that arises from hair follicle matrix cells (1, 2). Pilomatricomas are most commonly located in the head and neck and usually occur in the first two decades of life (2, 3). The usual presentation is that of a hard, usually solitary, mobile, slow growing mass of the dermis or subcutaneous tissue that may cause ulceration or a discoloration of the superficial skin (1, 4).
Histopathologically, pilomatricomas are characterized by the presence of eosinophilic keratinized cells, called shadow or ghost cells, and basalloid cells (1, 2, 4). Calcification is a common histopathologic feature of pilomatricoma while ossification is rare (1). The aim of this case report is to present a rare case of a pilomatricoma of the arm in a 33 year old female that was characterized by extensive ossification and to familiarize the general surgeon with this, known to pathologists and dermatologists, clinical entity.
A 33 year old female, with a free medical history, presented to our surgical department because of an asymptomatic mass on her left arm that she had first noticed about half a year ago. Clinical examination revealed a solitary, hard, mobile, well circumscribed nodule with the superficial skin being completely healthy, that was considered a foreign body reaction.
The tumor which measured 1x0,7x0,6 cm, was removed with a fusiform surgical excision. Macroscopical examination revealed a nodular tumor located in the deeper layers of the dermis adjacent to the subcutaneous tissue. The overlying skin was healthy (Fig 1). Microscopically it consisted of solid islands of shadow with extensive ossification. Even the usual nests of small basaloid cells were absent (Fig 2). The diagnosis of pilomatricoma with extensive ossification was established.
Pilomatricoma is a tumor of hair matrix that is almost always benign (2) with less than 20 cases of malignant transformation having been reported in the literature (3). The most common anatomical location is the head and neck region(1-5), with 40 -77% of all cases occurring in that area, followed in frequency by the upper extremities, the trunk and the lower extremities (3). Pilomatricomas most often present before the age of 20 years, and especially among children, with a male to female ratio of about 1 to 1,5-1,75 (5) (1). The clinical presentation is that of a firm or hard, mobile, well demarcated nodule, either deeply subcutaneous and invisible or superficial with possible erosion of the skin (1, 4). Pilomatricomas generally develop as a solitary lesion although multiple pilomatricomas have also been reported (1). In our case, the preoperative diagnosis was incorrect as the presence of a nodule in the arm of a 33 year old woman is not typical of pilomatricoma
Histopathologically, pilomatricomas are composed by uniform basalloid cells, with prominent nuclei and eosinophilic keratinized anucleated cells, called shadow cells (1, 2, 4). Basaloid cells are usually less in number than shadow cells, and sometimes there are no basaloid cells. Shadow cells are identified by the lost nuclei, which leaves a central unstained area and are characteristic of pilomatricoma. They are found towards the center of the tumor and may form masses, whorls or stacks. Calcification is a common feature, while dystrophic ossification or melanin pigmentation is rare. (1, 2, 4)
Based upon histopathological findings Kaddu et al (5) propose that pilomatricomas may be categorized into four distinct morphological and chronological stages: early, fully developed, early regressive and late regressive, which show the natural history of pilomatricoma. Early stage pilomatricomas are small and cystic and lined by a basaloid epithelium and containing shadow cells. Fully developed pilomatricomas are large, cystic and oval lined by a basaloid epithelium and containing shadow cells. Early regressive pilomatricomas are characterized by basaloid cells, without though apparent basaloid epithelium, inflammatory infiltration and shadow or multinucleated giant cells. Late regressive pilomatricomas have no epithelial component, contain numerous shadow cells but no basaloid cells, have little or no inflammatory infiltrate and may present calcification and ossification (5). In the present case the pilomatricoma was considered to be a late regressive pilomatricoma.
Differential diagnosis of pilomatricoma include sebaceous, trichilemmal, dermoid and epidermoid cyst, calcified lymph node, metaplastic bone formation, foreign body granuloma, calcified hematoma, hemangioma, cutaneous osteoma, osteochondroma, trichoepithelioma and basal cell epithelioma (1, 3, 6). The diagnosis can generally be made with a clinical examination but requires careful examination and a high index of suspicion (1, 3). Fine needle aspiration can aid the diagnosis (2, 3).
Recommended treatment of pilomatricoma is ideally by incision and curettage (4) but can also be managed by surgical excision (4, 6). The recurrence rate of pilomatricoma is very low following complete surgical excision (1, 6).
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- FIGURE 1: Hematoxylin - eosin stain showing a tumor located in the deeper dermis with normal overlying skin (x 20)
- Figure 2: Hematoxylin - eosin stain of the tumor showing islands of shadow cells and areas of extensive ossification (A: x 100, B: x 200)