Added Value of SPECT-CT Imaging in the Diagnosis of Unilateral Active Mandibular Hypercondylia in Adult: A Case Report and Review

Planar bone Scintigraphy has been frequently used to assess the active or inactive nature of mandibular hypercondylia. We report here the case of a patient whose diagnosis of active mandibular hypercondylia was retained after a complement with SPECT/CT imaging, the planar bone scan being negative. This case confirms the use of SPECT/ CT as the examination of choice for full assessment of mandibular hypercondylia in adults. Using bone Scintigraphy SPECT/CT improves both sensitivity and specificity of diagnosing this condition.


Introduction
Mandibular hypercondylia is a rare and autonomous bone disease due to the excessive growth of the condylar cartilage induced seemingly by a disruption of the feedback loops between the different histological layers leading to a persistence of the multiplication of prechondroblastic cells. Mandibular hypercondylia affects the overall development of the mandible and this condition is characterized clinically by atypical facial asymmetry, with a pronounced mandible anatomy, a disturbed occlusion, and a tilted occlusal plane [1]. Planar bone scintigraphy has been frequently used to assess the active or inactive nature of this situation [2] [3].

Patient and Method
The patient is a 43-year-old female, with no significant pathological history, who has had mandibular asymmetry for 10 years. She is directed to the nuclear medicine department for a scintigraphic evaluation of condylar activity following the diagnosis of left mandibular hypercondylia, which was revealed after completing dental panoramic examination supplemented by a craniofacial diagnostic CT scan.
Bone scintigraphy was completed in two stages: Acquisition of early images, The acquisition of images was performed with a Siemens gamma camera model Symbia T6 2010. The analysis was done using a visual and quantitative approach. A relative bone fixation of 55% (or more) was considered pathological.

Results
The planar bone scintigraphy did not show any asymmetry with radio tracer uptake in the early times (vascular and tissue), nor any abnormality in bone fixation in the late stage between the two mandibular condyles (Figure 1    Although the diagnosis can be formally established on histopathological exam, the radiological assessment following clinical examination remains essential to the diagnostic orientation. Information provided from a dental panorama and teleradiographic assessment, or diagnostic CT scan mostly allow the diagnosis of mandibular hypercondylia to be established.  [3]. In a context of clinical and radiological diagnosis of hypercondylia, a positive bone scan shows the active nature of the disease and allows therapy to be adapted. The molecular imaging techniques commonly used are planar bone scintigraphy and single photon emission computered tomography (SPECT) which can be analysed quantitatively and qualitatively [5].

Discussion
For most authors, SPECT can guide surgical management [6] and for others SPECT/CT could be used to measure residual activity after a condylectomy [7]. Condylectomy consists of a surgical excision of the cartilaginous cap, seat of the prechondroblastic cells, resulting in a definitive cessation of the pathological process. It is a key stage in the management of active hypercondylia [8].
In our study, all the modalities of bone scintigraphy were used. Planar imagery was negative at early and late stages but the complement by SPECT/CT made it possible due to fusion images to correlate the hyperfixation area of the tracer with the area of hyperplasia on the CT scans, increasing thus the sensitivity of the bone scintigraphy [9] [10] allowing the retained diagnosis of active unilateral mandibular hypercondylia.

Conclusion
This case confirms the fact that the SPECT/CT should be the examination of choice for the assessment of mandibular hypercondylia in adult; it improves both the sensitivity and the specificity of bone scintigraphy with a low irradiation rate and good value for money.