Oral myopericytoma: a rare pediatric case report and a review of the literature

Myopericytoma is a rare mesenchymal neoplasm with perivascular myoid differentiation that arises most commonly in middle adulthood. The lesion generally involves the subcutaneous tissue of distal extremities. Myopericytoma of the oral cavity is extremely rare. Herein we report a case of oral myopericytoma in a pediatric patient, who was treated via a conservative approach with a follow up of 8 years. The case is followed by a literature review. To our knowledge this is the first documented case of oral myopericytoma affecting a patient of such a young age. A 6 years old boy was referred to the maxillofacial surgery department for the evaluation of a solitary growth of the right maxillary buccal and palatal gingiva. Histology and immunohistochemistry confirmed the diagnosis of myopericytoma. Our patient was treated by local excision with no recurrence in 8 years of follow up. Conservative approach should be considered for the treatment oral myopericytoma especially in young patients in tooth bearing areas.


Background
Myopericytoma (MPC) was first described in 1996 as a slow-growing, well-circumscribed nodule of 2 cm or less, affecting mostly the skin and superficial soft tissues of distal extremities in adults. Recently, few rare cases of head and neck MPCs were described [1][2][3].
Most cases of MPC are benign. Nonetheless, few malignant and /or recurring cases were described [10,11]. In the oral cavity only one case of malignant MPC was reported [2].
A detailed case report of a 6 year old patient diagnosed with oral MPC is described, followed by a literature review.

Case presentation
A 6 years old boy, ASA 1 (American Society of Anesthesiologists physical status 1) was referred to a maxillofacial surgeon in November 2012, for the evaluation of a solitary growth of the posterior right maxilla.
Oral examination revealed a reddish, well-circumscribed and firm nodule that measured in its largest diameter about 2 cm. The mother of the patient noticed the lesion about a month before the initial examination. Main complaint upon presentation was bleeding from the area of the lesion while brushing the teeth. In order to establish better differential diagnosis and to undercover whether the lesion originates in the bone (meaning a central epicenter), causing bone destruction or whether it is a lesion of the soft tissue alone, the patient was sent to perform imaging. A Panoramic X-ray ( Fig. 1) and cone beam computed tomography (CBCT) failed to show any pathological change of the right maxilla.

Open Access
Owing to the obscure nature of the lesion and the young age of the patient, an incisional biopsy was performed immediately under local anesthesia and sent urgently to the pathological department (one of the considered and alarming differential diagnosis being Lymphoma and Leukemia). After receiving the pathological report based on the incisional biopsy (diagnosis of MPC), the patient underwent excisional biopsy of the lesion under general anesthesia, and a diagnosis of MPC was once again established based on histological and immunohistochemical analysis (Figs. 2, 3, 4). The incisional and excisional biopsy were performed by the Principal Investigator (Prof. Abu El-Naaj, an Oral and Maxillofacial Surgeon). Types of suture that were used (incisional and excisional biopsy, respectively) were Silk 3*0 and Vicryl 4*0, single interrupted. The excisional biopsy procedure was performed under general anesthesia in order to relieve the patient's anxiety and also in order to ensure the excision of the lesion and closure of the site are performed under the best medical conditions and maximal control. The operation itself lasted about an hour. Postoperatively, the patient received antibiotics (amoxicillin) and analgesics.
No further treatment was necessary as the lesion was fully excised.
After the final diagnosis was established and the postoperative healing was uneventful (Fig. 5a), the patient remained under close follow up (Fig. 5b). During the first year the patient was examined every 3 months and later on, once a year. During each follow up session, clinical examination was performed. Once a year, a panoramic Xray was performed.
To present date, 8 years postoperatively, no recurrence was detected.

Discussion and conclusions
MPC is a slow-growing benign neoplasm composed of cells that show apparent differentiation towards spindleshaped perivascular myoid cells called myopericytes [1,12].
The term myopericytes describes neoplastic pericytes exhibiting smooth muscle differentiation around vascular channels [13], thus-the neoplasm arising from these cells is consequently termed MPC [4,14].
MPC of the oral cavity is a rare entity with only few cases reported in the literature: three were reported in the tongue [4,15,16], two in the buccal mucosa [1,2] two in the lips [10,17] and one in the alveolar mucosa [3] ( Table 1).
MPC was first described by Requena et al. in 1996 as an alternative designation for solitary myofibroma [14] and was adopted 2 years later by Granter, Badizadegan and Fletcher who described the MPC as a tumor of concentric periluminal proliferation of bland, round to ovoid cells [12]. In 2002 it was defined and classified by the World Health Organization as a soft tissue neoplasm with differentiation toward pericytic/perivascular tumors [6]. Later on, Granter et al. added the tumors with features of infantily-type myofibromatosis in adults, glomangiopericytoma (GPC), glomangiomyoma and angioleiomyoma (ALM) into the MPC category [12].
MPC is described as a subcutaneous nodule of 2 cm or less [11,22]. MPC most commonly arises in the dermis or subcutaneous tissue of the extremities [1,2,4,15,23,24]. The lower extremities are the most commonly affected site, followed by the upper extremities, the head and neck region and the trunk [10]. Oral presentation is extremely rare [1,2,4,15].
Malignant transformation was reported once in the oral cavity [2].
MPCs have been reported to arise in immunodeficient patients. The clinical presentation of MPC in HIV positive patient is unique-occurring outside somatic soft tissue, including bronchus, tongue, vocal cord, brain, hepatobiliary system and spinal epidural tissue [16,25]. In addition, an association between EBV and immunosuppression was first reported by Calderaro in 2008 [26], however EBV-MPCs are uncommonly reported [25].
Being a rare entity, MPC can be easily misdiagnosed. Histological differential diagnosis include myofibroma, myofibromatosis, glomus tumor, perivascular epithelioid cell tumor, and hemangiopericytoma [27]. According to the literature, preoperative MRI and ultrasound investigations are found to be insufficient or misleading sometimes [28,29].
Excisional biopsy and histological examination are mandatory for a definitive diagnosis. Perivascular myoid cells are seen arranged concentrically around thin-walled vascular channels [19], but these findings must be further confirmed by immunohistochemical analysis where myopericytes are immunoreactive for smooth muscle actin, CD34 and calponin but rarely for desmin [3,30]. Application of strict morphologic criteria and appropriately selective immunohistochemical markers which were mentioned earlier will help in distinguishing MPC from its alike in the oral cavity [1,4,15,17].
MPC is treated by surgical excision with good prognosis. Wide local excision is the recommended treatment to prevent recurrences, with a careful follow-up [31].
Recurrences are rare [24], most likely due to poor circumscription of the lesion, extension of the tumor beyond the main lesion or malignancy [19].
There is a considerable debate regarding the treatment of oral MPC. Either local excision or wide local excision may be the choice of treatment. One should take into consideration many factors, such as the age of the patient and the region of the lesion; buccal, lingual or labial mucosa may undergo wide local excision without any serious consequences. The described case of a 6 years old boy with a maxillary lesion presented a surgical challenge. A true wide local excision in this case mandates posterior maxillectomy, with significant mutilation and morbidity. Therefore, excision of the lesion was the definite treatment, with a very strict follow-up, including imaging of panoramic x-rays. In addition, fiber optic observation, in order to refute the suspicions that the tumor has penetrated/invaded into the maxillary sinus was performed.
In conclusion, conservative approach should be considered for the treatment oral MPC especially in young patients in tooth bearing areas. More studies are required in order to achieve established conclusions.