Ankylosis of the Temporomandibular joint is a condition affecting the masticatory system that ranges from limitation to complete restriction of mouth opening, other features includes retarded growth of mandible, leading to facial assymetry and is most commonly due to trauma, such as condylar fracture with involvement of the articular surface, trauma from obstetric forceps, infections like advanced arthritis and some systemic diseases. [1, 2, 3, 4]
Hypomobility affects surrounding structures as well as the joint itself. Ankylosis arising in early childhood usually leads to facial asymmetry and in rare cases also to upper airway obstruction or obstructive sleep apnoea [1, 4]. The maxilla is usually affected secondarily, causing shortening of the posterior facial height.
Thus facial asymmetry is the classic feature in unilateral cases. The chin deviates towards the affected side, and the vertical height of the affected side is reduced when compared with the unaffected side.
On the other hand, complete limitation of the mouth opening and symmetrical recession of the chin are typical characteristics of bilateral ankylosis. Timing of the surgery, the type of operation, and the policy of treatment vary from one center to another. However, the main principles include resection of the ankylosed segment, use of interpositional material, plus early, aggressive and persistent postoperative physiotherapy. [3, 5, 6, 7]
Prof(Dr.)Sobhan Mishra is currently the head of the department, department of Oral and Maxillofacial Surgery, Institute of Dental Sciences, S’O’A University, Bhubaneswar, India. E-mail: email@example.com.
Dr. Ramanupam Tripathy is currently Reader in department of Oral and Maxillofacial Surgery, Institute of Dental Sciences, S’O’A University, Bhubaneswar, India.
Dr. Satyabrata Patnaik is currently a senior lecturer in department of Oral and Maxillofacial Surgery, Institute of Dental Sciences, S’O’A University, Bhubaneswar, India.
Dr. Pankaj Kumar Panda is currently continuing his internship in Institute of Dental Sciences, S’O’A University, Bhubaneswar, India. E-mail: firstname.lastname@example.org
Cases of congenital ankylosis has also been reported, True congenital ankylosis of the T.M.Js is rare. Therefore possess scanty literature. The exact pathogenesis is unknown. [8, 9]
The various proposed hypotheses include :
•Anomalous fusion of embryonal mesenchyme in early development during embryogenesis.
•An abnormality of the stapedial artery in the fetus.
•Hypervitaminosis A and early loss of neural crest
•TMJ ankylosis is also noticed with some congenital malformations such as Treacher-Collins syndrome and Pierre Robin’s syndrome.
In the year 2002 (HAKIM AND METWALLI) proposed that ankylosed joints can be grouped to the relation of their ankylosed mass to the surrounding vital structures, especially at the base of the skull base, interpreted from C.T. 
According to them: (based on C.T interpretation.).
Class I: Unilateral & bilateral ankylosis, the condyle and Glenoid fossa retain their original shape, and the maxillary artery is in normal anatomic relation to the ankylosed mass.
Class II: There is unilateral or bilateral bony fusion between the condyle and the temporal bone. The maxillary Artery is in normal anatomic relation to the ankylosed Mass.
Class III: The distance between the maxillary artery and the Medial pole of the condyle is less on the ankylosed side than in the normal side or the maxillary artery runs within the Ankylotic bony mass (best seen on coronal C.T).
Class IV: The ankylosed mass appeared fused to the base of the skull and there is extensive bony formation, especially from the medial aspect of the condyle to the extent that the ankylosed bony mass is in close relationship to the vital structures at the base of the skull such as the pterygoid plates, the carotid and jugular foramina and foramen spinosum and no joint anatomy can be defined from the radiograph. (This is best visualized on axial C.T).
This new classification gives the surgeon opportunity for the careful surgical planning and achieves better surgical results with minimum operative complications. 
A 15 year old male patient, reported to the hospital service for an investigation of TMJ Ankylosis. He had undergone bilateral surgical procedures of the temporomandibular joint 10 years ago. Patient was unable to report about the exact nature of surgery performed, now presented with complete Type IV, bilateral temporomandibular joint ankylosis. The surgical treatment included bilateral interpositional gap arthroplasty with a sling of rotated temporalis muscle as the interpositioning material.
Preoperative work-up included interviewing the patient to ascertain history of the defect and physical examination of the patient along with measurement of the interincisal distance. Radiological evaluation included 3-D CT scanning. However here, A well-defined radiolucency with multicystic appearance was seen within the usual p
icture of T.M.J ankylosis of a radio-opaque mass obliterating the normal architecture of the joint , giving the onlooker an illusion of a
n anomaly within anomaly .
Surgical procedure involved approaching the joint by traditional Alkayat-Bramley incision that is a preauricular incision extending into the temporal region. After reflection of periosteal flap and exposing the temporalis fascia, the dissection proceeded from a point that is 1cm below the zygomatic arch and 1cm to 2cm within the tragus, to avoid injury to the zygomatic branch of the facial nerve, the dissection proceeded in this plane till the joint was reached.The fused ankylotic mass when reached was found out to be nothing but air filled cavities obliterating the ankylotic mass at the site (FIGURE 4).
Which was apparently a great relief since the cavities appeared to be non-pathological, and without any cystic lining or discharge.
The surgery was continued with resection of the ankylotic mass and interpositioning of temporalis muscle sling. (FIGURE.5)
T.M.J ankylosis is an abnormality which not only causes skeletal alterations but also adversely produces alteration in soft tissue configuration. Secondary effects on the soft tissues surrounding the mandible occur in the form of shortening of the pterygo-masseteric muscle sling and the ligaments attaching the mandible to the skull base (sphenomandibular and stylomandibular ligaments); El-Sheikh et al., (1996) . The masticatory muscles may become hypertrophic as a result of long-standing isometric contractions. Hypertrophy of the temporalis muscle may lead to thickening and elongation of the coronoid process.
The suprahyoid muscles also become shorter and hypertrophic as they try to pull the chin inferiorly and simultaneously posteriorly causing shortening of the chin–hyoid distance, and thus contributing to partial obstruction of the airway, (El-Sheikh et al., 1996) . The degree of recession and asymmetry of the mandible depends on the growth condition and the time of onset of ankylosis .
Diagnosis of a fibrous ankylosis is more difficult; since the soft tissue fibrosis is not visible by conventional radiogra¬phic examinations. Osseous components of the T.M.J in fibrous ankylosis present as normal image, or as small areas of erosion, but the joint space is reduced in association with a limited mandibular opening movement. T.M.J osseous components may remodel as an attempt to adapt to the new situation .
Since 1930, radiographic images have been used as an important diagnostic tool in TMJ diseases. However the major problems are the overla¬pping of structures and image distortion .
Now again going back to the history of radiography, Conventional tomography was once used most frequently to image the TMJ. Conventional film-based tomography is designed to repre¬sent more clearly objects lying within a plane of interest .
Since the introduction of computed tomography (C.T), which has superior low-contrast resolution, film-based to¬mography has been used less frequently nowadays . The techniques are successful in detecting the shape of the condyle, joint outline, and osseous changes (including flattening, osteophytosis, sclerosis, and erosion .
Three-dimensional reformatted images have also been considered for determining the soft tissues and osseous component images. Currently, three-dimensional computed reconstruction allows elaboration of realistic and spatially accurate images for diagnosis and surgical planning .
Hence radiography is an essential diagnostic tool for TMJ ankylosis. Current methods include 3-dimensional C.T, and M.R.I and recently, the use of three- dimensional CT (3D-CT) prior to surgery has been advocated [11, 15].
C.T provides adequate information about condyle, mandibular fossa, articular eminence and surrounding tissues. Switching the image slices, it is possible to evaluate the condyle medial pole and lateral pole as well as the central region. Data from sagittal and coronal slices are the most useful for studying TMJ ankylosis. Normally in all complete Type IV ankylosis, 3D-CT reveals the ankylosed mass fused to the base of the skull with is extensive bone formation, especially from the medial aspect of the condyle to the extent that the ankylosed bony mass is in close relationship to the vital structures at the base of the skull such as the pterygoid plates,(FIGURE 6,7) the carotid and jugular foramina and foramen spinosum and no joint anatomy can be defined from t
he radiograph with reduced vertical height of the ramus .
During a regular course of C.T examination of T.M.J ankylosis an unusual picture was revealed. It elicited expansile osteolytic process within the affected joint bilaterally and was projected as a definite radiolucency. The internal structure invariably depicted fine septa crossing the lesion in a random pattern, giving it a soap bubble appearance that was multilocular. The above interpretation created a great pandemonium bringing the differential diagnosis to a crossroad of three interpretations, one that of to aneurysmal bone cyst and second of a traumatic bone cyst and third of an air sinus extended from mastoid air sinuses within the ankylotic mass.
Aneurysmal bone cyst is a condition that develops secondarily within another lesion of bone,most frequently it is associated with central giant cell tumours.Usually occurs in the 2nd & 3rd decade of life and with history of trauma.
Aneurysmal bone cyst is a contradictory term since it is neither aneurysmal nor a cyst, it is nothing more than central giant cell tumour with large blood filled spaces that lack an endothelial lining and are not under arterial pressure. It is not truly aneurismal because the blood filled spaces contain young fibroblast rather than endothelium. So, aneurysmal bone cyst represents a giant cell tumour that has larger vascular spaces and may attain a larger size as there is no difference in histopathologic features or biologic behavior between a central giant cell lesion and aneurismal bone cyst.
Aneurysmal bone cyst will classically present as a multilocular radiolucent lesion that the cortices, giving the appearance of soap bubble.
Traumatic bone cyst is a benign, non-neoplastic lesion, predominantly among younger age group that is below 20 years. Traumatic bone cyst was first described by LUCAS & BLUM (1929)  as a separate disease entity. However, RUSHTON M.A in 1946  established the diagnostic criteria for this cyst. It comprises generally single lesion without any epithelial lining, surrounded by bony walls and either lacking contents or containing liquid or connective tissue.
Various etiopathogenesis have been proposed:
1. Bone tumour degeneration.
2. Altered calcium metabolism.
3. Low grade infection.
4. Local alteration in bone growth.
5. Venous obstruction.
6. Increased osteolysis,
7. Intermedullary bleeding.
8. Local ischaemia.
But the most widely accepted mechanism involves microtrauma and subsequent intermedullary bleeding, with osteoclastic activity and the elimination of trabeculae within the cancellous bone compartment, thus giving rise to a cystic cavity. Clinically, patients were asymptomatic until the time of surgery and the cysts constituted casual findings. Radiographically, traumatic bone cyst appear as a radiotrasparent image with irregular or scalloped but well defined margins. The size is variable and a fine sclerotic margin is sometimes seen.
Recently, the term traumatic bone cyst is outdated since it does not have an epithelial lining. Now it is called idiopathic bone cavity because it persists as a cavity in bone containing no specific diagnostic elements.
In the present case, though the patient is of younger age group that is second decade, the history of surgery, associated with another condition that is ankylosis and radiolucent lesion with cavitation, the possibility of aneurysmal bone cyst is rule out because in the C.T, it clearly shows that there is no blood filled spaces and also well defined margins.
The possibility of idiopathic bone cavity is more likely as the patient is in the second decade of life, with history of surgical intervention of the temperomandibular joint, radiolucent lesion with cavitation and more importantly not lined by epithelium. Moreover our surgical intervention elicited nothing but hollow air filled cavities which contradicted the interpretations elicited from C.T reports, though the close proximity of the mastoid air cells to the cystic areas in the ankylosed mass, gives a possibility, if the air sinuses of the mastoid had extended forward following previous surgical intervention. The surgery was uneventful and the patient has had a 1 year follow up with no complications.
In spite of radiographic advances through advanced CT imaging and other adjunctive techniques, there are a plethora of pathologies which often gives a blurred picture of the existing pathology. Clinical correlation and detailed medical history is a must for differential diagnosis and also needs a good literature review to correspond to the existing pathologies. The case presented here also had a very rare and rather confusing presentation anomaly in the CT scan, which was tabled for clearer picture with due clinical picture and presentation.
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