J.A. García de Marcos¹, F. Alamillos Granados², A. Dean Ferrer³, J.J. Ruiz Masera⁴, A. Vidal Jiménez⁵, 
J.M. Calderón Bohórquez¹, B. Valenzuela Salas¹

Recibido: 29.08.05

Aceptado: 15.11.05

1 Médico Residente. Servicio de Cirugía Oral y Maxilofacial.
2 Especialista en Cirugía Oral y Maxilofacial. Fellow of the European Board of Oral and Maxillofacial Surgery.
3 Jefe de Sección. Servicio de Cirugía Oral y Maxilofacial. Fellow of the European Board of Oral and Maxillofacial Surgery.
Profesor asociado de la facultad de medicina. Universidad de Córdoba.
4 Especialista en Cirugía Oral y Maxilofacial. Servicio de Cirugía Oral y Maxilofacial.
5 Médico Residente. Servicio de Anatomía Patológica. Hospital Universitario «Reina Sofía». Córdoba, España.

Correspondencia:
J.A. García de Marcos.
C/ Antonio Acuña, 10, 5ºAizq.
28009. Madrid, España.
E-mail: pepio2@hotmail.com

Introduction

Pilomatrixoma is a benign neoplasm of the skin that arises from hair follicle matrix cells.^1-3 In 1880 Malherbe and Chenantains described the lesion as a benign subcutaneous neoplasm that they believed originated in the sebaceous glands. In 1922 Dubreuilh and Cazenave described the histopathologic characteristics of this neoplasm that included islands of epithelial cells and ghost cells. In 1961, Forbis and Helwig discovered that the original cell was in the external cellular layer of the hair follicle and they proposed the term pilomatrixoma to describe the lesion (Ref. Lan and cols. and Thinakaran and cols.).^2,4

Other terms have been used for defining this lesion such as pilomatricoma, calcifying epithelioma of Malherbe, or tricomatrioma. ^1,2

Although pilomatrixoma may appear at any age it is more common during infancy and adolescence and a second peak in incidence is observed in patients between the ages of 50-65.² It more commonly affects the female sex. It is of unknown etiology.¹ The area of the head and neck is most commonly affected (50% of lesions), followed by the upper extremities, trunk and lower extremities.² Clinically it presents as a solitary subcutaneous nodule that is hard, firm and painless, and which grows slowly over months or years. It is generally asymptomatic, but some are associated with inflammation or ulceration. Its size varies and it can measure 0.5 to 3 cm in diameter. It tends to have a sphere shape and the overlying skin can be of the normal skin color, or pinkish, purplish red or it can be ulcerated.^1-3 The tumor generally moves freely over the underlying tissue.²

The treatment of choice is surgical excision with relapse being uncommon following complete resection. Malignant transformation is extremely rate.^1,2,5

FNA (Fine Needle Aspiration) is being used increasingly for the diagnosis of pathological masses of the head and neck, and in expert hands it has high sensibility and specificity. ^3,4,6 The highly cellular smear, with isolated cells showing a high nuclear/cytoplasm ratio can lead pilomatrixoma to be mistaken for a malignant tumor.^4,7 We present the clinical case of pilomatrixoma which was initially diagnosed as a low-grade malignant epithelial tumor.

Case Report

Female patient, 17 years old, attended our department for the study and treatment of a nodule in the skin by the right parotid area that had been evolving for six months. It was painful to palpation and it was growing steadily. She had no medical or surgical history of interest.

On physical exploration a preauricular nodule could be appreciated with a 1 cm diameter that was situated 1 cm away from the preauricular fold. It was hard in consistency and it was adhered to the skin and not to the underlying tissue (Fig. 1). Unspecific, round and swollen lymph nodes could be felt with a submandibular, bilateral location.

Ultrasound and Magnetic Resonance (MR) was carried out together with FNA. The Ultrasound examination revealed an oval formation measuring 1 x 0.6 cm in size that had heterogeneous echogenicity with vascularization, which led to the suspicion of an angiomatous condition. The MR showed an oval lesion that was hypointense on T1-weighted images as well as on T2- weighted images. It was well-defined, and situated in subcutaneous cellular tissue in the right preauricular region and adjacent to the skin. The lesion was independent of the parotid gland (Fig. 2). The suspected diagnosis after MR was of adenopathy or angioma. FNA showed high cellularity, a high nuclear/cytoplasmic ratio, prominent nucleoli, and basaloid cells with a primitive appearance (Fig. 3A). A few multinucleated giant cells could also be appreciated (Fig. 4A). FNA reported a non-specific epithelial tumor of low-grade malignancy.

In view of the information gained from her medical examinations, radiological tests and FNA, the clinical diagnosis was of malignant adnexal tumor.

Two weeks after the first consultation and under local anesthesia, the lesion was resected together with the overlying skin and the adipose tissue that was surrounding it. The lesion was yellowish and hard in consistency (Fig. 5). The histological study revealed cells organized in circles, cells with nuclei, peripheral basaloid cells and ghost cells with no nuclei in the center (Fig. 3B). There were areas of foreign body reaction, with granulomatous reaction to ghost cells in areas where there was large amounts of keratinized debris (Fig. 4B). The anatomopathologic result was of pilomatrixoma. Nine months after the surgery there were no signs of relapse or complications.

Discussion

Although the etiology of pilomatrixoma is unknown, the myotonic dystrophy gene and the polyoma virus have been identified as possible factors connected with its appearance. Many investigations have shown that pilomatrixoma is frequently associated with the mutations of the CTNNB1 gene, which directly imply a change in the regulation of ß-catenin/LEF. In addition pilomatrixoma has been linked with a series of genetic diseases such as myotonic dystrophy, xeroderma pigmentosum, Rubinstein-Taybi syndrome, Turner syndrome, Goldenhar syndrome and sarcoidosis.¹ Similar changes to those identified in pilomatrixoma have been observed in patients with Gardner’s syndrome or basal cell nevus syndrome.¹

In the head and neck it is generally to be found in the cheek, the preauricular area, forehead, neck, periorbital region and scalp.³ The size of the lesions varies between 0.5 and 3 cm in most cases,^2,3 although giant lesions of up to 15 cm have been described. The case we present was situated in the preauricular region and the widest point was 1 cm.

The diagnosis can be suspected taking into account the location of the tumor and its firm consistency, which when pressed shows its «faceted stone» texture and «tent sign» due to the calcification of the lesion. The differential diagnosis in the head and neck should be made with the dermoid and epidermoid cysts, calcifying lipoma, branchial cyst, giant cell tumor, lymphatic calcifying nodules, chondroma, degenerative fibroxanthoma, foreign body reaction, calcifying hematoma, cutaneous osteoma, hemangioma and tumors of the parotid gland.^1-3

The radiological tests are of little value when diagnosing pilomatrixoma. Computed Tomography shows a subcutaneous lesion that is clearly demarcated and with calcifications. Magnetic Resonance shows images with high intensity on T2-weighted images, which correlate with the bands formed by basaloid cells appearing in the histopathological study. The sound scan is a fast, innocuous test that can help with the diagnosis by determining the depth of the mass.² Ultrasound shows a hyper-echoic edge corresponding to the connective tissue of the capsule, and a hyper-echoic center corresponding to the epithelial cells of the center. The calcifications can also be appreciated with ultrasound which also helps to clarify the relationship of the lesions in the parotid region with the parotid gland.

FNA is used as a diagnostic preoperative method.^2,4 It is currently considered a test with a better cost-benefit ratio for diagnosing tumors of the head and neck.⁶ The principal diagnostic error for this type of tumor when using FNA as a diagnostic study, is a false positive result for malignancy.^2,3,4,8 The cytological differential diagnosis should include epidermoid carcinoma, basil cell carcinoma and metastases of smallcell carcinoma.⁴ The results can deceive when ghost cells are not found in the aspirate, which is a frequent occurrence. High cellularity, high nuclear/cytoplasmic ratio, prominent nucleoli and the primitive appearance of basaloid cells can lead to an erroneous diagnosis of malignancy,⁷ as occurred in our case. However, the basal cells of pilomatrixoma are uniform and there is more of an open chromatin structure with small nucleoli. Carcinomatous cells are darker and more pleomorphic with chromatin that is fine and dense, and macronucleoli. Another characteristic of carcinomatous cells is the additional presence of a prominent population of lymphoid cells, a considerable number of plasmatic and eosinophilic cells with occasional aberrant lobulated cells, and tingible body macrophages.⁷ In addition to these differences, the medical history, presence of characteristic ghost cells, absence of atypia and of mitoses, presence of calcium deposits and multinuclear giant cells should help in making a correct diagnosis.^4,7 If absent, obtaining a second opinion and repeating the aspiration, together with the use of airdried smears, will help in the diagnosis in those cases that are difficult.^5,7

There is no correlation between histological type, the time over which the nodule has been evolving clinically, or the size of the tumor.¹ In view of spontaneous remissions not being described with this type of lesion, treatment should consist in surgical excision. Occasionally the overlying skin has to be resected due to the tumor adhering to the dermis.^1-3 It is very rare for pilomatrixoma to recur after surgery, and the incidence of this is 0-3%.^2,6 The appearance of a second lesion in another area of the body is rare, and the risk diminishes progressively with age.⁸

In addition to pilomatrixoma, there are other benign lesions of the head and neck that can be diagnosed erroneously as malignant lesions after carrying out FNA. They are the following: branchial cyst that can be confused with the well-differentiated epidermoid carcinoma, and the lymphatic node, with reactive lymphadenopaty, that can be confused with a centroblastic/centrocytic type of lymphoma.

Conclusion

When faced with a lesion that is clinically suggestive of an adnexal tumor and with FNA that indicates a low-grade epithelial tumor, it should be stressed to the anatomopathologist that there is a possibility of pilomatrixoma so that the cytological analysis is reviewed.

Acknowledgments

We would like to thank Dr. Pérez-Seoane Orduña (Assistant pathologist. Department of Pathological Anatomy. Hospital Universitario Reina Sofía. Córdoba, Spain).

References

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