Myositis ossificans traumatica of the medial pterygoid muscle following a third molar extraction

Abstract

Myositis ossificans (MO) is a rare disease involving heterotopic ossification in the muscle or soft tissue. Myositis ossificans traumatica (MOT) disease presents as a calcification within the injured muscle, resulting from a single or repetitive injury. There are few reports of MOT in the masticatory muscles. The case of a patient with MOT in the medial pterygoid muscle caused by a complication related to the extraction of an erupted upper third molar is reported. The major symptom was severe trismus. Despite surgical treatment, the disease relapsed. MOT can lead to serious consequences for the patient. Its aetiopathogenesis needs to be better understood, so that the most appropriate treatment is established and relapses are minimized. This will improve the quality of life of these patients.

Myositis ossificans (MO) is a rare disease involving heterotopic ossification in the muscle or soft tissue. MO is divided into myositis ossificans progressiva (MOP) and myositis ossificans traumatica (MOT), also called myositis ossificans circumscripta. MOT disease presents as a calcification within the injured muscle, resulting from a single or repetitive injury. Particularly in cases where there is no history of injury, a malignant lesion should be considered in the differential diagnosis.

There are few reports of MOT in the masticatory muscles. Most of the cases reported in this region have involved the masseter muscle. Eight cases of unilateral injury of the medial pterygoid muscle have been reported in the literature.

The diagnosis of MOT is based on the history of trauma and on clinical, radiographic, and microscopic features. Severe limitation of jaw opening has been reported.

The case of a patient with MOT in the medial pterygoid muscle, caused by a complication related to the extraction of an erupted upper third molar, is reported; the case relapsed despite surgical treatment.

Case report

A healthy 36-year-old Caucasian female patient underwent extraction of the right upper third molar in June 2008 at a different facility. On the ninth postoperative day, she developed trismus and pain. On the advice of her dentist, physical and thermal physiotherapy, broad-spectrum antibiotic therapy, and non-steroidal anti-inflammatory drugs were initiated. Four weeks later, the severe trismus persisted. Although no secretion was obtained during aspiration of the masticator space, also performed by the general dentist, clinical features compatible with infection, such as trismus and pain, were still present. Physiotherapy was maintained, but there was minimal improvement in maximal mouth opening (MMO).

Four months later, her MMO was still limited and maxillofacial magnetic resonance imaging (MRI) revealed a mass compatible with calcification of the right medial pterygoid muscle. MOT was considered the most likely clinical diagnosis. In March 2011, an excisional biopsy was performed at another medical facility using a right submandibular approach, confirming the diagnosis. The range of motion improved immediately after the surgery, but the patient developed pain, swelling, and trismus again.

At 5 months postoperative, the patient was referred to the Department of Oral and Maxillofacial Surgery of Vila Penteado General Hospital, São Paulo, Brazil. Physical examination revealed a small amount of swelling in the right mandibular ramus, causing facial asymmetry. Palpation of the temporalis and masseter muscles was normal. At that time, she was unable to open her mouth wide or to perform protrusive or excursive movements. Palpation of the medial pterygoid muscle was not possible. Occlusion was stable.

A panoramic radiograph showed a calcification extending from the right mandibular ramus to the pterygoid process. Computerized tomography (CT) scanning revealed an ossification in the right medial pterygoid muscle, showing a central region of low attenuation ( Fig. 1 ). Three-dimensional CT showed the position and shape of the ossification and the dimension of fusion of the medial pterygoid muscle to the pterygoid plates ( Fig. 2 ). The results of laboratory blood tests for calcium, ionized calcium, phosphorus, alkaline phosphatase, and parathyroid hormone levels were within normal limits.

Fig. 1
CT scan showing ossification in the right medial pterygoid muscle.

Fig. 2
Three-dimensional CT showing the dimension of the fusion of the medial pterygoid muscle to the pterygoid plates.

Surgical removal of the ossification was planned with the aid of prototyping. The patient was operated on with fibre optic-assisted nasotracheal intubation, under general anaesthesia. A right submandibular approach was used, as well as an additional intraoral incision to improve access to the mass. An L-shaped osteotomy of the lateral aspect of the ramus including the entire mass was performed. A gap of 3 cm was left and an interpositional abdominal fat graft was placed between the medial aspect of the ramus and the pterygoid plates.

Microscopic examination of the surgical specimen revealed areas of muscle atrophy replaced by fibrous connective tissue and areas of ossification consistent with the diagnosis of myositis ossificans ( Fig. 3 ).

Fig. 3
Close-up of organizing intramuscular fibrous tissue, showing osteoid differentiation (magnification 250×).

The patient underwent intense physiotherapy for 1 month and the MMO achieved was 34 mm. However, the patient developed trismus again in the second postoperative month (MMO 9 mm), and CT revealed an ossification in the medial pterygoid muscle. The current treatment plan includes another surgical intervention, resectioning a larger area of the ramus and removal of the entire muscle, followed by intense assisted physiotherapy for several months.

Discussion

Including our case, there are only 43 cases of MOT involving the masticatory muscles in the English-language literature. Its treatment represents a challenge for clinicians and little information is known about its prognosis.

We have presented a case of MOT in the medial pterygoid muscle caused by a complication, probably an infection inadequately dealt with by the general dentist, related to the extraction of an erupted upper third molar, a simple procedure with little manipulation required. The intensity of the trauma may not be related to the onset of MOT, as observed in other reported cases involving the medial pterygoid muscle, such as: local anaesthetic injection in the mandibular foramen, extraction of the lower third molar, cervical immobilization, odontogenic infection, and alcohol injection.

Our patient was female; the reported male to female ratio is 2.4:1. The mean age of affected patients is 38.1 years, as reported by Boffano et al., which is compatible with our case who was 36 years old.

The aetiology and pathogenesis of this disease is not completely understood. It is a rare disease of the maxillofacial region, and the masseter muscle is the most involved. An explanation for this could be that the masseter is a broad muscle and covers the lateral surface of the mandibular ramus, and is therefore susceptible to damage as a result of trauma. MOT in other masticatory muscles may be caused by iatrogenic trauma.

The most frequent symptom is trismus, but others like pain and swelling have also been observed. The absence of symptoms is also reported in the literature.

Restricted mouth opening is a common problem encountered in oral and maxillofacial surgical practice, so when a patient is unable to open their mouth wide, a careful history must be obtained and thorough physical examination done. In such cases, despite being a rare condition, MOT should be considered by the oral and maxillofacial surgeon.

According to Boffano et al., the pathognomonic feature of MO is a well-circumscribed, high-attenuating periphery, with a low-attenuating central portion. In the case reported, we observed a low-attenuating image in the middle of the mass.

The most widely accepted treatment is complete resection of the ossification after maturation. However, surgical techniques including osteotomies are also indicated, particularly when complete removal would be more debilitating because of the close relationship between the heterotopic bone and the skull base, as for the medial pterygoid muscle. In the present case, two osteotomies were performed, one L-shaped on the lateral aspect of the ramus and the other 3 cm from the first, and a fat graft from the abdomen was placed as interpositional material, as suggested by Thangavelu et al. Rattan et al. reported a case in which they used a buccal fat pad as an interpositional material between the medial surface of the mandibular ramus and the pterygoid Plates.

For appropriate surgical planning, we suggest three-dimensional CT because this improves the view of the ossification position and shape. Furthermore, we stress the importance of prototyping, especially in the simulation of the best location for osteotomies, thereby minimizing surgical risks.

According to Thangavelu et al., the excision of MOT is best performed during the mature phase of the lesion, when it is well-delineated from the surrounding skeletal muscle. However, since MOT is a debilitating condition, we tend to adopt surgical management at an early stage of the disease.

MOT can be a differential diagnosis of malignant diseases, like osteosarcoma, and its zonal architecture is the most important histological feature to distinguish one from the other. Despite the pathognomonic characteristic of MOT, well-developed lesions may be totally ossified, with little or no evidence of the cellular component. In the present study, the specimens showed areas of muscle atrophy replaced by fibrous connective tissue and areas of ossification.

As with our patient, other individuals have experienced repeated relapses despite surgical treatment. According to Thangavelu et al., resection is important and the presence of an interpositional material can impede and restrict the recurrence of MOT. Although this procedure was used for our patient, relapse occurred. It is generally agreed that intensive physiotherapy should be part of postoperative care. However, our patient ceased the assisted physical therapy after the first postoperative month, which may have contributed to the relapse of restricted mandibular opening. This has also been suggested by Steiner et al.

In conclusion, MOT is a rare disease that can affect the maxillofacial region, with serious consequences for the patient. Its aetiopathogenesis needs to be better understood, so that the most appropriate treatment is established and relapses are minimized. This will improve the quality of life of these patients.

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Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Myositis ossificans traumatica of the medial pterygoid muscle following a third molar extraction
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