Pilomatricoma: Forget me not.

Pilomatricoma is a benign skin neoplasia, which is not commonly encountered in general practice. The diagnosis is often made only after histopathology. The present case report is of a 30-year-old woman who presented with swelling in neck, which was diagnosed as pilomatricoma only after excision. The idea of reporting this case is that pilomatricoma is not rare in occurrence but rarely diagnosed because of lack of confirmation of excised swelling and it is imperative that it should be kept in the differential diagnoses of all superficial skin tumors by dermatologists and surgeons.

INTRODUCTION

Pilomatricoma, or pilomatrixoma, or calcifying epithelioma of Malherbe is a benign skin neoplasia originating from hair follicle matrix cells.[1] It usually develops slowly and is known as a single or sometimes multiple benign solid lesions lying just under or in the skin.[23] Pilomatricomas represent 0.12% of all skin tumors.[4] We report here a case of pilomatricoma diagnosed after surgical excision with the help of histopathology.

CASE REPORT

A 30-year-old female presented to skin department with complaint of swelling over the middle of neck on right lateral side since 1 year. The onset was gradual and initially the size was very small (pea sized) but slowly over last 1 year it had grown to the size of an almond. It was painless to begin with but there was an occasional dull ache in the swelling. There was no associated fever or malaise. The patient denied any history of trauma prior to onset. Family history and past history of patient was unremarkable.

On examination there was swelling in the right side of neck of 2.5 × 2.0 cm size [Figure 1]. It was smooth on palpation, moderately firm to hard in consistency and minimally tender to touch. It could be moved laterally with a little restriction in caudocephalic movement. It appeared to be fixed with the skin with no attachment to the underlying tissues. There was no rise of local temperature, scar, sinus, or any other remarkable feature. General physical and systemic examination was found normal.

Figure 1

A subcutaneous swelling on right middle of neck

A provisional clinical diagnosis of sebaceous cyst was made. Surgical excision was planned after blood investigations. The swelling was excised under local anesthesia and sent for histopathological examination. On gross examination the excised mass appeared to be calcified during excision. The histopathology features were suggestive of pilomatricoma [Figures 2 and 3].

Figure 2

Pilomatrixoma. Photomicrograph showing basaloid cell at the periphery and “ghost cells” on the right side of the field (H and E, ×100)

Figure 3

Pilomatrixoma. Higher magnification showing abrupt keratinization with “ghost cells” (H and E, ×400)

DISCUSSION

Pilomatricoma is a relatively rare skin neoplasia. It may affect individuals at any age, incidence peaks on the first and sixth decades of life. It is more common in women (1.5 to 2.5:1) among young people, 40% happen before 10 years of age and 60% before 20 years.[15] New hair follicles are not formed after birth, only some are activated during puberty. If they are located in very deep layers, differentiation induction agents will not act properly on them. These partially differentiated follicles would form the pilomatricomas.[1] These tumors can be familial related to Gardner's syndrome, Steinerd's disease, and Sarcoidosis.[6]

Pilomatricomas are often mistaken for “small round blue cell” tumors in children, or for Merkel cell carcinoma, basalioma, and metastatic small cell carcinoma in adults, with possible over aggressive therapeutic approach.[7] A recent study suggests that trisomy-18 is a consistent feature in pilomatricoma, suggesting that genes carried on this chromosome such as that for the antiapoptotic oncoprotein BCL2 may have a role in the growth and differentiation of this benign self-limited tumor.[8]

The clinical history of pilomatricama is typical of a slowly enlarging mass, irregularly contoured, which is fixed to the skin but slides freely over the underlying tissues, often with a discoloration, which varies from red to bluish-purple.[9] Pilomatrixomas are often misdiagnosed on preoperative evaluation. In a series of 51 histologically proven pilomatrixomas, Wells et al found that the diagnosis during reference was incorrect in 94% of cases, and the preoperative diagnosis was incorrect in 57%.[10] In a recent series of 346 pilomatrixomas, the preoperative diagnosis was accurate and consistent with the pathological diagnosis of pilomatrixoma in only 28.9% of cases.[5] Finally, Kumaran et al reported a correct preoperative clinical diagnosis in 46% following retrospective review of 78 excised pilomatrixomas.[11] Incorrect preoperative diagnoses most commonly included unidentified masses, as well as epidermoid cysts, sebaceous cysts, dermoid cysts, nonspecified cysts, and foreign bodies.[511]

Histological characteristics include ghost cells in the center with basophilic nucleated cells in the periphery. Calcification is present in 70%–95%.[112], Clinically skin and adjacent tissue infiltration, ulceration, and histologically - presence of nuclear pleomorphism, atypical mitosis, central necrosis is suggestive of malignancy[13] Cytomorphologic characteristics of PM are reliable enough for correct preoperative diagnosis in adequate specimens. However, the best results are achieved when fine-needle aspiration cytology is performed by an experienced cytologist after obtaining all clinical data.[7]

A rare malignant counterpart, pilomatrix carcinoma, has been described and nearly 90 cases have been reported in the literature. It is locally aggressive and can recur. In several cases, metastases have been observed. Many key features are similar between these benign and malignant counterparts; the primary differentiating characteristics include a high mitotic rate with atypical mitoses, central necrosis, infiltration of the skin and soft tissue, and invasion of blood and lymphatic vessels.[1415]

Surgical excision with clear margins is the treatment of choice, otherwise there may be recurrence due to incomplete resection.[9]

CONCLUSION

Pilomatricoma is a benign tumor of the skin, which is not rare in occurrence but rarely diagnosed preoperatively and it is imperative that it be kept in the differential diagnoses of all benign skin tumors by dermatologists.