Title page
Non-traumatic myositis ossificans of the Right masseter muscle: a case
report and review of the literature
Authorship List:
1-Reza Sharifi : Assistant Professor, Department of Oral and
Maxillofacial Surgery, Cranio maxillofacial research center. School of
Dentistry, Tehran University of Medical Sciences, Tehran, Iran
2- Lotfollah Kamali Hakim: Resident of Oral and Maxillofacial Surgery,
School of Dentistry, Tehran University of Medical Sciences, Tehran,
Iran.
3-Saeed Hasani Mehraban: Resident of Oral and Maxillofacial Surgery,
School of Dentistry, Tehran University of Medical Sciences, Tehran,
Iran.
4-Amirali Asadi: Resident of Oral and Maxillofacial Surgery, School of
Dentistry, Tehran University of Medical Sciences, Tehran, Iran. *
*Corresponding author: Amirali Asadi – Email:
Amirali_a_2003@yahoo.com
Non-traumatic myositis ossificans of the Right masseter muscle: a case
report and review of the literature
Abstract:
Myositis ossificans (MO) is a rare disease in which ossification
develops in the muscle or soft tissue. MO traumatica is recognized by
ossification of the soft tissues after acute or repetitive trauma,
burns, or surgical procedures. It usually involves the extremity
muscles. In the head and neck region, the masseter is most commonly
involved in MO traumatica. Surgical resection of the ossified tissue has
been the most commonly used treatment for this disorder, with a high
postoperative recurrence rate. We report a case of non-traumatic MO of
the Masseter muscle with different size round calcifications and to
review the literature reported data about MO traumatica involving the
masseter muscle.
Key words:
Myositis – Ossificans – masticatory – muscle –
Key Clinical Message:
Myositis ossificans is a disease with the main feature of formation of
heterotropic bone involving muscle or any other soft tissue. Its main
clinical features in Oral and Maxillofacial region are trismus, pain and
swelling in some cases. Surgical excision is the main treatment.
1.Introduction:
Myositis ossificans (MO) is a rare disease in which ossification
develops in the muscle or soft tissue. MO is divided broadly into
myositis ossificans progressiva(MOP) and myositis ossificans traumatica
(MOT). MOP is an autosomal dominant disease in which multiple,
heterotopic ossifications develop in the systemic muscles, fascias,
tendons, and ligaments, sometimes within familes. MOT,also called
traumatic myositis ossificans, myositis ossificans circumscripta,
localized myositis ossificans, or fibrodysplasia ossificans
circumscripta, is a disease in which muscles are ossified after trauma
or inflammation (1).
Unlike MOP, MOT is often remitted through surgical treatment, including
excision of the ossification, some patients have repeated relapses and
are refractory to treatment (2).
In the head and neck region, the masseter is most commonly involved in
MOT because it is on the lateral side of the mandible and is most likely
to receive external forces directly (3).
The aim of this article is to present and discuss a case of
non-traumatic MO of the Masseter muscle with different size round
calcifications.
2.Presentation of case:
A 24-year-old male was admitted to our outpatient clinic in Shariati
Hospital Tehran, Iran. He complained of swelling in right masseter
region from 1.5 year ago. During physical examination painful and
movable separate masses were evident in the right ramus of mandible, the
patient also mentioned pain on chewing and mouth opening, He had no
limitation on mouth opening and the skin over the right cheek region and
the intraoral soft tissue, were normal. The right parotid duct exhibited
normal salivary flow. He denied any blunt trauma to the area and his
medical history and systemic review were unremarkable. A core needle
biopsy was taken from the patient 8 months before and that report was
“Fibromuscular tissue with a few blood vessels”. There was no history
of familial involvement and the patient denied any anesthesia or
dysesthesia.
MRI was taken from the region and a mass with 55*32 mm diameter in right
masseter muscle with scattered signal void foci related to
calcifications with few enhancing after Gd injection. The lesion was
high on T2 signal and iso on T1(Figure 1 A-D).
The CT revealed a 65*29*51 mm soft tissue mass which was located in
right masseter muscle with foci of round calcifications: Radiologist
suggested Hemangioma the first Differential Diagnosis for the lesion
(Figure 2 A_D) CT Angiography was done but no Vascular lesions was
found.
As we noticed calcification in masticatory muscles, the laboratory tests
including Calcium, Alkaline phosphatase, Phosphorus, and Vitamin D were
ordered and they were all within normal ranges.
Eventually, the patient’s history, and the clinical and radiographic
findings, allowed us to diagnose Myositis Ossificans involving the right
masseter muscle.
Intraoperatively, Under local anesthesia, the right masseter muscle was
subjected to blunt dissection and eleven calcified masses were
identified and excised. Approximately, masses measured 3 mm to 1 cm in
diameter (Figure 3 A, B).
Histopathologic examination revealed relatively mature calcifications
formed from irregular bone trabeculae, surrounded by masseter muscle
fibers. (Figure 4 A, B)
Post-operative radiographic images showed some remained round
calcification after surgery located in regions with difficult intraoral
access. (Figure 5 A, B)
postoperative course was uneventful and no abnormality of masticatory or
sensory function was noted. After surgery, the patient had some pain in
the right cheek region, with restriction of jaw movement. Therefore, A
period of physiotherapy was carried out and the patient was instructed
for active and passive mouth opening exercises.
After 6 months follow up the patient returned to our clinic and he was
satisfied with resolution of swelling and increased MMO (Figure 6). The
patient is now under supervision for further progression of the lesion
and If condition worsens, revision surgery will be performed.
3-Discussion:
Myositis ossificans is a heterotopic ossification of muscular tissue
which is benign and is characterized by well differentiated bone
formation (4).
Trauma is the most frequent etiological factor seen in almost 60–75%
of the cases (5). It is most frequently encountered in the arm,
shoulder, thigh, and hand, in order of frequency (6). Fortunately, MOT
is rare in the maxillofacial region. The masseter muscle is commonly
involved because of its position on the facial skeleton, which makes it
more prone to traumatic injuries. Incidence of the pterygoid and
temporalis muscle involvement is rarely reported in literature(3).
MO may develop at any age, but is most often seen in adolescents and
young adults (7).
Theories have been discussed about etiology, such as myositis ossificans
being a step in an organizing hematoma’s development. It has also been
suggested that osteoblasts escape from periosteum and migrate to soft
tissue and create this condition. Another theory is mechanical trauma
that can cause osteoblasts to be pushed into muscle and therefore result
in ectopic calcification in a muscle (8). Burns, infections, and drug
abuse are other rare factors which may cause MO (9). Nontraumatic MO is
very rare in the literature (10). Repetitive microtrauma, tissue
ischemia, and inflammation were addressed as the causative mechanisms of
the non-traumatic MO (11). the most widely accepted theory states that
trauma to skeletal muscles induces the expression of bone morphogenic
protein at the site of injury, which in turn stimulates the primitive
stem cells to differentiate into osteoblasts, resulting in heterotopic
ossification (12). Table-1 reviews 6 cases of myositis ossificans in
masseter muscle in the literature previously published (2, 13-18)
As mentioned in the table, female is more frequently involved than
males, In all of the cases trauma to the masticatory system or infection
is noticed. As our patient did not give any obvious history of trauma,
we feel our case is unique of being nontraumatic and having no
simultaneous predisposing factors, we can name it as idiopathic Round
Calcification of masticatory muscles, which is rare.
4-Conclusion
Myositis ossificans is a disease with the main feature of formation of
heterotropic bone involving muscle or any other soft tissue. Its main
clinical features in Oral and Maxillofacial region are trismus, pain and
swelling in some cases. It is more common in females. Surgical excision
is the main treatment for MO and it is essential that clinicians visit
these patients on regular intervals to monitor for signs of
inflammation, decreased range of motion, or radiographic evidence of
recurrent calcified mass formation.
Author Contribution:
Majid Beshkar: Carried out the surgery
Lotfollah Kamali Hakim: Reviewed and revised the article
Saeed Hasani Mehraban: Reviewed and revised the article
Amirali Asadi: Wrote the manuscript in consultation with other authors
Conflicts of interest:
The authors have no conflict of interest to declare.
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Figure legends:
Figure-1(A_D): Preoperative MRI revealed a mass in right masseter
muscle with round calcifications.
Figure-2 (A_D): Preoperative CT scan revealed round calcifications at
right masseter region.
Figure-3: The lesion surgically excised which shows Fragments of round
different size calcifications.
Figure 4: Histopathologic examination revealed relatively mature
calcifications formed from irregular bone trabeculae, surrounded by
masseter muscle fibers.
Figure-5: Post-operative radiographic images showed some remained round
calcification after surgery located in regions with difficult intraoral
access
Figure-6: patient’s mouth opening at 6 months follow up