CASO CLÍNICO

 

Benign myoepithelioma: presentation of a case report

Mioepitelioma benigno: presentación de un caso clínico

 

 

A. Ostrosky¹, D.M. Villa², M. González², F. Klurfan²

1 Jefe del Servicio de Cirugía Maxilofacial.
2 Concurrente del Servicio de Cirugía Maxilofacial.
Hospital Mariano y Luciano de la Vega. Moreno, Argentina

Correspondence

 

 

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ABSTRACT

We present a case of benign myoepithelioma of the parotid gland, which was treated by superficial gland lobectomy along with facial nerve conservation. A differential diagnosis with other benign tumors with similar clinical signs such as pleomorphic adenoma is made. The importance of a correct anatomopathologic diagnosis is also stressed, as is making a differential diagnosis with epi-myoepithelial carcinomas.

Key words: Benign myoepithelioma; Parotid tumors.

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RESUMEN

Se presenta un caso de mioepitelioma benigno de glándula parótida, el cual fue tratado mediante la lobectomía superficial de la glándula, con conservación del nervio facial. Se hace el diagnóstico diferencial con otros tumores benignos como el adenoma pleomorfo, con el cual comparten una clínica similar. También se destaca la importancia de un correcto diagnóstico anatomopatológico, en este caso haciendo diagnóstico diferencial con los carcinomas epi-mioepiteliales.

Palabras clave: Mioepitelioma benigno; Tumores parótida.

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Introduction

There is much controversy as to the classification of myoepithelial or clear cell tumors. Two varieties can be distinguished, benign and malignant. The term epi-myoepithelial carcinoma was introduced by Donath in 1972 and accepted by the WHO, and it refers to a different pathological entity that can be confused with myoepithelioma.

Benign myoepithelioma is an uncommon tumor of the salivary glands, representing approximately 1% of the total of these tumors.¹ It is encapsulated and slow-growing, and it is nearly always asymptomatic. It affects a wide age range, and the mean age is 40. The parotid gland is affected 48% of the time, the submaxillary glands 10% and minor glands 42%.^2-3

Histologically, benign myoepithelioma is composed of myoepithelial cells. The presence of up to 5% of ductal epithelial cells is considered normal, while a large number of ductal formations will guide us towards a mixed tumor diagnosis. Five cellular patterns can be distinguished in benign myoepithelioma: 1) spindle cells, 2) plasmocytoid cells, 3) reticular pattern, 4) clear cells, and 5) combination of various types.^2-3 The rate of recurrence of this type of tumor is low when completely excised.

Malignant myoepithelioma has similarities and differences with the benign variety that has been described. It has medium-to-high grade malignancy. It arises principally in the parotid gland (65%). Histologically it has myoepithelial cells, but cellular atypia is observed together with neural infiltration and infiltration of neighboring structures. There may be distant metastasis and there is a tendency for recurrence in 60% of cases.^2-3

Epi-myoepithelial carcinoma is a low-grade malignant tumor. In contrast with myoepithelioma it has a biphasic tubular histological structure.^4-6 It has an internal layer made up of epithelial ductal cells, and an external layer of clear myoepithelial cells. The capsule may be incomplete. Batsakis (1992) classified this carcinoma into three subtypes: 1) with a predominance of clear myoepithelial cells, 2) with spindle shaped myoepithelial cells, and 3) with a predominance of ductal epithelial cell. Others classify the same tumor in two varieties, one tubular with two visible layers of cells and another solid with a predominance of clear myoepithelial cells. There is little cellular atypia and there is a low mitotic rate,⁷ although neighboring nerves and vessels tend to be invaded. It is slow-growing and generally asymptomatic although there may be general pain the region of the facial nerve, if the nerves are invaded. It appears generally in women in the 7th decade of life and 80% of the time it appears in the parotid gland. In 10% of cases distant metastasis has been reported and regional adenopathy in 20%. The rate of recurrence is between 20% and 50% and in general the course of the disease is prolonged due to recurrence.⁴

Benign myoepithelioma should be removed along the tumor borders.³ If it is completely resected recurrence is rare. Malignant myoepithelioma should be resected with wide security margins, and radiotherapy should follow.³

With regard to epi-myoepithelial carcinoma, the treatment of choice is resection of the tumor with wide margins. Various authors advise radiotherapy in those tumors with a diameter that is greater than 4 cm although it has been shown to have little radiosensitivity.⁴

 

Case report

Female patient, 67 years of age, was referred to the department of Maxillofacial Surgery of our hospital with a concentrated mass in the left parotid region. It had on palpation a pasty consistency, that was readily movable, and there were no signs of infection or disturbance to the skin. No adenopathy was felt in the neck lymph nodes. There was no pain of any type in the area of the tumor. During the intraoral examination no disturbance was observed. The time from onset was 3 years. The patient had no other systemic disturbance of relevance (Fig. 1).

A computed tomography was requested as a result of which it could be observed that the tumor was affecting the superficial lobe of the left parotid gland. There was no sign of any disturbance to neighboring tissue. Given the clinical signs, the presumed diagnosis was of benign tumor of the salivary glands (Fig. 2).

Under general anesthesia and using an extraoral approach, the tumor was removed and a superficial gland lobectomy of the parotid gland was carried out, and the facial nerve was preserved (Figs. 3 and 4).

The pathologic anatomy confirmed the diagnosis of benign myoepithelioma. The immunohistochemical analysis revealed typical markers for clear myoepithelial cells: actin, S-100 protein and vimentin⁸ (Figs. 7, 8 and 9).

There were no complications during the postoperative period. There was only paresis of the muscles around the operated side of the cheek, which remitted three months later. After a follow-up of a year there have been no signs of recurrence (Figure 5 and 6).

 

Discussion

It is of great important that pathologists with a wide knowledge of salivary gland tumors carry out the diagnosis, as there are many similarities in these pathologies that frequently result in incorrect treatment.

The surgeon should give special attention to the anatomopathologic report as a pathologist with little experience in this area can confuse benign myoepithelioma with epi-myoepithelial carcinoma, or with the malignant variety of myoepithelioma. In this case conservative surgery should be carried out, when surgery involving wide safety margins would be correct. Given these diagnostic errors, the recurrence of epi-myoepithelial carcinoma is relatively high (20-50%).⁵ Thus the high rate of recurrence of the malignant variety of myoepithelioma is as much as 60%. This can be due to diagnostic errors that lead to inadequate surgery in each case.

In addition, a differential diagnosis should be established with other glandular tumors: pleomorphic adenoma, adenocystic carcinoma, mucoepidermoid carcinoma, clear cell adenocarcinoma, acinic cell adenocarcinoma.

Given our experience, we are able to state that carrying out correct treatment in the first instance is of great important. While there is good prognosis for benign myoepithelioma, there is evidence of recurrence and malignant transformation following incomplete resection, either because of the malignant transformation of the remaining primary pathology, or due to regions that were initially malignant that were not included in the resection. For this reason we prefer, whenever possible, to remove this benign tumor while leaving at least a small safely margin if its location permits this.

 

Aknowledgments

Dr. Eduardo A. Mareso (Doctor of Pathology, Hosp. MLV, Moreno).

 

 

Correspondence:
Alejandro Otrosky
Arenales 1578- José C. Paz.
Buenos Aires, Argentina.
Email: diegomartinvilla@hotmail.com

Recibido: 18.04.06
Aceptado: 06.10.06

 

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