Parotid pilomatricoma: a case presentation and literature review

Abstract

Background

Pilomatrixoma is a rare benign tumor of the hair follicle. It is more common in children and women. The cervical and facial region are the most frequent location for this type of tumor. Due to its variable clinical presentations, it can sometimes be misdiagnosed as a malignant tumor of surrounding tissues, as described in our case.

The diagnosis confirmation is pathological.

Case presentation

We report the case of a 34-year-old patient, who presented a swelling in the right parotid region gradually increasing in size for two years, with no facial asymmetry. Clinical examination revealed a rounded, well-defined mass, fixed to the superficial plan, without any cervical lymph nodes. The MRI showed a tumor that seems to be evolving from the superficial lobe of the right parotid, suggesting a pleomorphic adenoma. Total excision of the tumor without margins was performed, preserving the parotid tissue and the facial nerve. The postoperative course was normal; and the pathological study confirmed the diagnosis of pilomatrixoma.

Conclusion

Pilomatrixoma is a rare benign tumor but it remains a differential diagnosis of large tumors of the neck and parotid. It is mainly a pathological diagnosis, The treatment of choice still complete surgical excision.

Background

Pilomatricoma, or calcifying epithelioma of Malherbe, is a rare benign tumor that develops from the cells of the hair follicles of the skin. It was first described in 1880 by Malherbe and Chenantois, but in 1961 the name “pilomatricoma” was proposed by Forbes and Helwig [1, 2]. Review by according to the literature, the pilomatrixoma occurs in children and young adults below 30 years of age [3].

In general, pilomatricoma tumors can be solid, partially solid or cystic, and may contain deposits of calcium, which explains why it’s called “calcifying epithelioma of Malherbe” [1]. The preferred approach for treatment is surgical excision with clear margins. This also reduces the risk of malignant transformation [4].

We report the case of a parotid location of pilomatrixoma; initially making it difficult to differentiate from a parotid gland tumor. The final diagnosis was confirmed by histology.

Case presentation

A 34-year-old patient, with no particular medical history, presented a swelling in the right parotid region evolving for 2 years, gradually increasing in size, with no facial asymmetry (Fig. 1). Clinical examination revealed a rounded, firm, painless, well-defined mass, fixed to the superficial plane and mobile to the deep plane, measuring about four centimeters in size. The overlying skin was red without other inflammatory signs. There was no trismus; or compression of the oropharynx. There were no cervical lymph nodes.

Fig. 1

Mass in the right parotid region

The patient had an MRI that showed a tumor in the right parotid region, with a low T1 and T2 signal, non-restrictive to diffusion, enhancing homogeneously after gadolinium injection, well-encapsulated, measuring 4.6 cm in size, and seems to be evolving from the superficial lobe of the right parotid. Apparent diffusion coefficient (ADC) was calculated to1.1, suggesting a pleomorphic adenoma (Fig. 2).

Fig. 2

MRI: tumor with an extension to the right parotid superficial lobe

The patient was informed about the surgery procedure. Our approach initially consisted in performing a superficial parotidectomy. Given the tumor size and its fixity to the skin, we performed a modified incision instead of the classic Lazy-S incision, taking all the infiltrated skin. Total excision of the tumor without margins was performed, the parotid tissue and the facial nerve was not dissected. We didn’t perform an intraoperative frozen section examination.

The postoperative course was good; facial motility was normal, and the patient returned home 2 days after surgery. The pathological study confirmed the diagnosis of pilomatricoma.

Histologically, it is a tumor proliferation made up of mummified epithelial masses and basophilic cell clusters without abnormal mitosis. Calcifications are present, with no signs of malignancy (Fig. 3).

Fig. 3

Pilomatricoma: tumor proliferation made up of mummified cell masses and non-atypical basophilic cells (HES * 100)

Discussion

Pilomatricoma, also known as Malherbe’s calcifying epithelioma [1], is a rare benign tumor with an incidence reported between 0.5% and 1.6% [5]. It arises from the matrix of the hair follicle and occurs before the age of 30 in 60% of cases, with 40% of tumors developing before the age of 10, and the highest incidence observed between 8 and 13 years of age [6]. It is more common in females, with a female-to-male ratio of approximately 3:2 [6]. Our reported case confirms the female predominance; and occurs in an adult patient.

Over 75% of pilomatrixomas, which are most commonly found on the head and neck, are located on the scalp, face, neck, or arms [7]. The parotid region is a frequent location for these tumors [7].

Pilomatricomas in the parotid region can be mistaken for parotid neoplasms [8]. Other common differential diagnoses for pilomatricomas in the head and neck have been described in the literature, including sebaceous cyst, ossifying hematoma, giant cell tumor, chondroma, dermoid cyst, foreign body reaction, degenerative fibroxanthoma, and cutaneous osteoma [9]. Diagnosis mainly relies on histopathological examination, with a high rate of diagnostic error [5]. Clinical examination of parotid pilomatricomas reveals a solid or cystic, slow-growing, mobile, and painless mass [8]. The overlying skin may have a reddish or bluish coloration, sometimes it looks like a vascular or malignant tumor infiltrating the cutaneous tissue. Deep extension may have been close to the superficial lobe of the parotid [8]. CT scan or MRI can differentiate pre-auricular pilomatricomas from parotid tumors, it also can evaluate the extension of voluminous tumors and their exact location near to noble structures [7].

Surgical excision of pilomatricomas is necessary because they do not regress spontaneously. The margins of excision should be clear, although margins of 1 to 2 cm recommended by some authors are likely excessive due to the benign nature of the disease. Malignant transformation is rare, with less than 20 reported cases, and usually occurs in older individuals. After a complete excision, pilomatricomas rarely recur, with reported rates ranging from 0 to 3% [4]. Therefore, surgical excision remains the treatment of choice, but long-term follow-up is essential [10].

Conclusion

Pilomatricoma is a rare benign tumor arising from the matrix of the hair follicle. It is mainly a pathological diagnosis, but it remains a differential diagnosis of large tumors of the neck and parotid. The treatment of choice is complete surgical excision of the tumor. Recurrence and malignant degeneration of the lesion are uncommon.