Zygomatic Air Cell Defect - Magnetic Resonance Imaging of the Temporomandibular Joint Compared with Panoramic Radiographs

Abstract

The aim of the study was to analyze zygomatic air cell defect (ZACD) incidence using magnetic resonance imaging (MRI) and validity of panoramic radiograph as a comparative method of ZACD diagnostics. The connection between ZACD incidence, age, left/right temporomandibular joint (TMJ) and comorbidity with diagnosis of TMJ disorder was analyzed. Panoramic radiographs and MRIs of 140 TMJs of 70 consecutive patients with previously confirmed TMJ diagnosis were compared in the study. A grading system (4-point scale from '0' for absence to '3' for most extended pneumatization) was used to determine low signal on MRIs as pneumatization of temporal bone. ZACD was diagnosed in 22 joints of 15 patients (incidence, 20.4%), with seven patients having bilateral appearance. In the joints of nine patients, ZACD was identified as extensive accord-ing to the grading scale. The validity of ZACD findings on panoramic radiographs compared with MRI findings yielded 0.45 sensitivity and 0.98 specificity. There was no relation (p>0.05) between comorbidity of ZACD and TMJ disorder, either by age or side of the body. More prevalent ZACD in our MRI analysis than in other researches based on panoramic radiographs could be explained by the expected superimposed osseous structures in the area of articular eminence.

Keywords: Croatia; Magnetic Resonance Imaging; Radiography, Panoramic; Temporal Bone; Temporomandibular Joint Disorders; Zygoma - diagnostic imaging.

Fig. 1

Magnetic resonance image of the temporomandibular joint of a 62-year-old female with marked low signal area extending into the articular eminence (a); it corresponds to the finding seen on panoramic radiograph (b).

Fig. 2

Superposition of adjacent bone structures on panoramic radiograph (a) was shown in a 57-year-old female patient. Pneumatization visualized on temporomandibular joint transcranial radiography (b) and magnetic resonance image (c).

Fig. 3

The grading system used for the low signal area classification within the temporal bone overlying the glenoid fossa extending anteriorly into the articular eminence. From the arbitrary center of the glenoid fossa (C), a parallel line was drawn with the connecting line of the lowest edge of articular eminence (A) and external on the lower edge of external auditory meatus (M). A vertical line from point C is the border since low signal does not go beyond this line from the posterior region and it is marked ‘0’. The greatest spreading of low signal was marked ‘3’.

Fig. 4

Magnetic resonance image of the temporomandibular joint in the central parasagittal plane of a 36-year-old male patient with anterior disc position. Low signal area within the temporal bone overlying the glenoid fossa extending into the articular eminence – the highest degree of low signal wide spreading was grade ‘3’ according to the grading system used in this study.

Fig. 5

False-positive findings of pneumatization can occur on panoramic radiograph (a). Pneumatization on cone-beam computed tomography (b) and magnetic resonance imaging (c) was missing in a 42-year-old female patient.