Cytodiagnosis of Pilomatrixoma from an Uncommon Site with Unusual Presentation

Abstract

Pilomatrixoma or pilomatricoma is an uncommon benign tumor of hair matrix origin, which most commonly occurs in the head and neck region and upper extremities. In this study, we report a case of pilomatrixoma of a 35-year-old female presenting with left-leg swelling with surface ulceration, clinically thought to be malignant. Fine-needle aspiration cytology (FNAC) of the lesion showed clusters of basaloid cells with round to ovoid nuclei, nucleated squamous cells, and anucleated squames and clusters of shadow cells. Acytological diagnosis of pilomatrixoma was made. Subsequent surgical excision and histopathological examination confirmed the diagnosis. This case highlights a rare site of presentation and the role of FNAC in preoperative diagnosis of this benign tumor for proper management.

INTRODUCTION

Pilomatrixoma or pilomatricomais a relatively uncommon benign tumor that originates from the matrix cells at the base of the hair.[1] The most common location of this tumor is the head and neck region, followed by the upper extremities and rarely in the lower extremities.[2,3] It presents as a solitary, slow-growing dermal or subcutaneous nodule; however, clinical diagnosis is often difficult or misdiagnosed.[4,5] Histologic features of this tumor are well recognized, but cytological features often produce diagnostic difficulties.[6]

CASE REPORT

A 35-year-old female presented with a nodular ulcerated swelling measuring 3 × 2.5 cm over the left lower leg since the past 5 years [Figure 1]. The nodular lesion was well-circumscribed, firm with surface ulceration. The patient attended Fine-needle aspiration cytology (FNAC) clinic with a clinical suspicion of malignancy. On physical examination, the lesion was not fixed to the underlying bone and no inguinal lymphadenopathy was detected.

Figure 1.

External clinical photograph. Ulcerated nodular lesion in the lower leg

Fine-needle aspiration was performed using a 22-gauge needle. Cytological smears were cellular, showing clusters of basaloid cells having round to oval nuclei, nucleated squamous cells, and anucleated squames. Few fragments of shadow cells adherent to basaloid cells were also noted [Figure 2a and b]. A cytological diagnosis of pilomatrixoma was made.

Figure 2.

Fine-needle aspiration cytology showing (a) clusters of basaloid cells admixed with squamous cells and anucleated squames (May-Grünwald-Giemsa ×200); and (b) cluster of shadow cells adherent to basaloid cells (MGG, ×400)

Excision biopsy and histopathologic examination of the resected specimen showed typical features of pilomatrixoma with basaloid cells in the periphery, shadow cells toward the center, and a few foreign body-type giant cells [Figure 3a and b].

Figure 3.

Sections showing (a) islands of basaloid cells and shadow cells with surrounding foreign body giant cells and inflammatory cells (H and E, ×100); Inset: Showing shadow cells in higher magnification; and (b) basaloid cells in higher magnification (H and E, ×400)

DISCUSSION

Pilomatrixoma is a relatively uncommon benign tumor of hair matrix differentiation, first described by Malherbe as benign calcifying epithelioma, as a tumor of the sebaceous gland.[7] Later on, the term was changed to “pilomatrixoma” because of its histogenesis from hair matrix cells.[1] The most common sites involved in this tumor are the head and neck region, followed by the upper extremities, trunk, andthe lower extremities.[2,3,8] This tumor usually occurs in children younger than 10 years of age and also in the second decade of life.[9] They are more commonly seen in women.

Clinically, this tumor presents as a soft to firm subcutaneous mass with intact overlying skin with average size 1.6 cm.[8] Correct clinical diagnosis is very rare and differential diagnosis includes epidermal cyst, dermoid cyst, cysticercosis, sebaceous cyst, sebaceous adenoma or carcinoma, capillary hemangioma, chalazion, rhabdomyosarcoma, and so on.[2,8,10] FNA of the lesion commonly reveals basaloid cells, squamous cells, anucleate squames, shadow cells, foreign-body giant cells, polymorphs, and calcification in variable frequencies.[8] As all these findings are not present in a single case, cytological misdiagnosis is common and includes epidermal inclusion cyst, adnexal tumor, squamous cell carcinoma, basal cell carcinoma, mucoepidermoid carcinoma, or even round-cell tumor.[8,11,12] When aspirates contain mainly nucleated squamous cells and squames, it leads to a wrong diagnosis of epidermal inclusion cyst. Predominance of basaloid cells can give a misdiagnosis of basal cell carcinoma or even round-cell tumor. In aspirates of pilomatrixoma, the presence of foreign-body giant cells is also variable. Moreover, they can be found in other lesions such as epidermal inclusion cysts, ruptured benign cysts, and panniculitis to squamous cell carcinoma.[8] Extreme calcification in pilomatrixoma may yield only calcified material and proper diagnosis may not possible. Hence, cytology has some limitations in the diagnosis of pilomatrixoma. Histopathologic examination provides the correct diagnosis and shows solid nests of basaloid cells with the formation of ghost cells with foreign-body giant-cell reaction, calcification, and ossification in some cases.

Our patient presented with an ulcerated nodule in the left lower leg. Clinical diagnosis of squamous cell carcinoma was given. In our case, FNAC yielded basaloid cells, squamous cells, anucleate squames, and shadow cells; which helped us arrive at a correct preoperative diagnosis. Histopathology also confirmed the diagnosis.

In our case, the site of the lesion, which was very uncommon, and the presence of surface ulceration led to a clinical misdiagnosis. Knowledge of the morphological spectrum of characteristic cellular components helps in correct preoperative diagnosis of pilomatrixoma by FNAC and helps in proper patient management.

Lastly, we have presented this case because of the rare location of the tumor and the malignant clinical presentation. This case also highlights the role of FNAC in arriving at a correct preoperative diagnosis.