Case Study: Circumscribed Myositis Ossificans of Masseter Muscle Causing Trismus


This article discusses an interesting case report of circumscribed myositis ossificans of the masseter muscle causing trismus with a review of literature on the subject. This rare disorder is characterized by dystrophic calcification leading to heterotopic ossification (presence of bone tissue where it is not usually present) of intramuscular connective tissue. Muscles of mastication are commonly involved in this condition.


Myositis ossificans involving the masseter muscle is rather rare. This condition is characterized by dystrophic calcification and heterotopic ossification of intramuscular connective tissue. Masticatory muscles are commonly involved.

Types of myositis ossificans:

Myositis ossificans progressiva – This is a rare congenital condition characterized by malformations involving great toes and progressive heterotopic ossification 1. Spontaneous mutation tends to be the cause of most of these cases. Genetic transmission is autosomal dominant 2.

Myositis ossificans circumscripta – This condition is largely limited to a single muscle and normally one of mastication. This is generally caused by progressive ossification of intramuscular hematoma, which could occur due to a muscle injury. This term is used to classically describe non-hereditary forms of myositis ossificans.

Pseudomalignant myositis ossificans – This is limited to soft tissue not associated with trauma. This condition can be mistaken for a malignant lesion but can also be [s2If !is_user_logged_in()]…

[/s2If][s2If is_user_logged_in()] considered a premalignant lesion 3.

Myositis ossificans associated with paraplegia – This type of myositis ossificans is known to arise out of complications of a spinal cord injury.

Case Report

63-year-old male patient reported to the outpatient department with complaints of:

  1. Difficulty in opening the mouth – 1 month duration
  2. Swelling over left side of cheek (bone-hard in nature) – 2 months duration

patient showing trismus

Clinical photograph of the patient showing trismus

Clinical photograph showing swelling
Clinical photograph showing swelling

The patient reported a medical history that included a trauma 3 months back, following which a pain developed when opening his mouth. This pain gradually subsided, but the extent to which his mouth could open became less and less.

CT imaging showed a well-circumscribed hypodense lesion involving the left masseter area. Patchy calcification could be clearly seen within the mass.

Axial CT shows well demarcated hypodense mass with calcified areas
The axial CT showed a well-demarcated hypodense mass with calcified areas.

Under general anesthesia, and therefore complete muscle relaxation, an attempt was made to open the patient’s mouth using a Macintosh laryngoscope. However, since it was still not possible to open his mouth due to severe trismus, an open approach to the lesion was preferred.


Figure showing the incision
A lazy man “S” incision is used to expose the lesion. After elevating the skin and subcutaneous tissue, the masseter muscle is exposed.

showing exposure of the lesion
Figure showing exposure of the lesion

The masseter muscle was split open, exposing the lesion. The circumscribed bony lesion was drilled out, and the wound was then closed in layers. Mouth opening after the surgery improved to two and half fingerbreadths.

Post op picture showing improved mouth opening following surgery
Post-op picture showing improved mouth opening following surgery

Patient was advised to perform mouth-opening exercises by placing a plastic top inside his mouth in order to improve mouth opening further still.

Image showing plastic top being used to perform mouth opening exercises
Image showing plastic top being used to perform mouth opening exercises.

This case is being presented for its rarity and to stress the importance of having an open mind in treating these patients.


Pathophysiology of myositis ossificans begins with an intramuscular haemorrhage, followed by the formation of vascular granulation tissue 4. Maturation of the granulation tissue results in fibroblastic proliferation with synthesis of chondroid and osteoid elements. Evidence of calcification may take 3-6 weeks to appear 5. Even though this is a benign and self-limiting disorder, it needs to be treated because it interferes with the patient’s ability to eat and maintain sufficient oral hygiene. A high index of suspicion and CT imaging goes a long way in clinching the diagnosis.

Surgery should be deferred until there is a substantially functional handicap to the patient.

Indications that surgery may be necessary include:

  1. Increasing functional handicap due to the lesion
  2. Rapidly increasing size of the lesion
  3. Patients who are refractory to conservative methods of treatment


This case is reported for its rarity.

Surgery is one of the options for managing these patients.

CT imaging helps in the diagnosis.

About The Author

Balasubramanian ThiagarajanDr. Balasubramanian Thiagarajan, is a Professor in the Department of Otolaryngology at Stanley Medical College in Chennai, Tamilnadu. He has authored a number of journal articles and case reports on otolaryngology and related topics, as well as three books.

References (click to show/hide)

  1. Cohen RB, Hahn GV, Tabas JA, et al. The natural history of heterotopic ossification in patients who have fibrodysplasia ossificans progressiva. A study of forty-four patients. J Bone Joint Surg Am. Feb 1993;75(2):215-9.
  3. A. J. Aboulafia, F. Brooks, J. Piratzky and S. Weiss, “Osteosarcoma Arising from Heterotopic Ossification after an Electrical Burn. A Case Report,” The Journal of Bone & Joint Surgery, Vol. 81, No. 4, 1999, pp. 564-570.
  4. Rattan V, Rai S, Vaiphei K. Use of buccal pad of fat to prevent heterotopic bone formation after excision of myositis ossificans of medial pterygoid muscle. J OralnMaxillofac Surgn 2008;66:1518-1522. Pmid:18571044
  5. Wiggins RL, Thurber D, Abramovitch K, Bouquot J, Vigneswaran N. Myositis ossificans circumscripta of the buccinator muscle: first report of a rare complication of mandibular third molar extraction. J Oral Maxillofac Surg 2008;66(9):1959-63. PMid:18718410 PMCid:PMC2548317


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One Comment

  1. sharmila rao
    Posted Jun 2014 at 12:32 am | Permalink

    Very interesting but where is the maxillo-facial surgeon?

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