Radiographic assessment of asymmetry of the mandible.

PURPOSETo assess the relationship between mandibular asymmetry and disorders of the temporomandibular joint.METHODSWe used advanced imaging of the temporomandibular joint to distinguish different causes of mandibular asymmetry. MR imaging and arthrography were applied to the temporomandibular joints of 11 patients presenting with mandibular asymmetry.RESULTSCondyle hyperplasia was identified as the cause of the asymmetry in 5 patients. In the other 6 patients the mandibular condyle was normal on the long side, but the short side of the face demonstrated a small condyle head, short condyle neck associated with disk displacement, internal derangement, and degenerative joint disease of the temporomandibular joint.CONCLUSIONSThese observations suggest that both condyle hyperplasia on the long side of the mandible and disk displacement and degenerative joint disease of the temporomandibular joint on the short side can cause mandibular asymmetry. It was concluded that MR imaging or arthrography can be valuable for understanding the cause of mandibular asymmetry and be effective in treatment planning.     

Masticatory muscle activity and hyoid bone behavior during cyclic jaw movements in man. A synchronized electromyographic and videofluorographic study

Synchronized electromyography (EMG) and videofluorography were used to relate the EMG activity from the suprahyoid and masseter muscles and the movement of the hyoid bone to different phases of the jaw open-close-clench cycle. The subjects investigated comprised 19 adult males with normal dentofacial appearances. Five subjects were excluded from the analyses because of a uniform suprahyoid EMG pattern during cyclic jaw movements. The results from the remaining fourteen subjects revealed that mandibular opening was preceded by suprahyoid EMG activity and movement of the hyoid bone in an upward-forward direction. During jaw opening and the first half of the jaw-open phase, EMG activity was registered exclusively from the suprahyoid muscles. The hyoid bone was moved downward-backward during jaw opening. Mandibular closing was preceded by masseter EMG activity and movement of the hyoid bone in a further downward-backward direction. During jaw closing the hyoid bone moved upward and forward. Discrete EMG bursts from the suprahyoid muscles were occasionally registered simultaneously with the masseter EMG activity during jaw closing. No absolute reciprocity existed between suprahyoid and masseter muscle activity during cyclic jaw movements. A period of no EMG activity from either the suprahyoid muscle group or the masseter muscle was noted during the jaw-open phase and the occlusal phase.     

Temporomandibular joint: surgically created disk displacement causes arthrosis in the rabbit.

To document a causal relationship between temporomandibular joint disk displacement and arthrosis, the disk was surgically displaced in one temporomandibular joint in each of three rabbits. The rabbits were sacrificed after 4 weeks and the mandibular condyles were studied radiographically and histologically. All three joints that underwent disk displacement had radiographic and histologic evidence of arthrosis, which included erosion of the bone, irregularity and fissure formation of the articular soft tissue cover, disruption of the subchondral layer of cartilage cells, and chondrocyte proliferation. No radiographic or histologic changes occurred in the joints that were untouched. The results suggest that surgically created disk displacement can cause arthrosis in the temporomandibular joint of the rabbit.     

Magnetic resonance evaluation after temporomandibular joint diskectomy.

The aim of this study was to investigate the value of magnetic resonance imaging after diskectomy of the temporomandibular joint. Magnetic resonance images were obtained before and 12 months after unilateral diskectomy without disk replacement. Magnetic resonance findings at follow-up were correlated to residual pain. At the follow-up, 20 of 28 patients were free of pain in the joint that had been surgically treated, four patients had mild pain, and four patients had significant residual pain. The magnetic resonance images at follow-up showed that the joint space was filled with soft tissue after diskectomy. In patients without pain at follow-up, this soft tissue had a magnetic resonance signal that was equal or higher than that of the muscles. In the four patients with significant residual pain and in one patient with mild residual pain, the soft tissue in the joint space between the condyle and glenoid fossa had a magnetic resonance signal intensity that was lower than the muscle. On the basis of findings in a previous study, the areas of low signal intensity were interpreted as fibrous adhesions. The study suggests that areas of low signal intensity in the joint space appear to be associated with residual pain and that magnetic resonance imaging could be a valuable tool for assessment of the temporomandibular joint after diskectomy.     

Developmental Changes of Laryngeal Dimensions in Unparalyzed, Sedated Children

Background: Knowledge of the influence of age on laryngeal dimensions is essential for all practitioners whose interest is the pediatric airway. Early cadaver studies documented that the larynx is conically shaped, with the apex of the cone caudally positioned at the nondistensible cricoid cartilage. These dimensions change during childhood, as the larynx assumes a more cylindrical shape. The authors analyzed laryngeal dimensions during development to determine if this relationship continues in unparalyzed children in whom laryngeal muscles are tonically active. The authors determined the relationships between the vocal cord, sub-vocal cord, and cricoid ring dimensions and the influence of age on these relationships.

Methods: Infants and children undergoing magnetic resonance imaging with propofol sedation had determinations of the transverse and anterior-posterior (AP) dimensions of the larynx at the most cephalad level of the larynx (vocal cords) and the most caudad level (cricoid). Most patients had an additional measurement (sub-vocal cord) at a level between the vocal cords and the cricoid ring. Relationships were obtained by plotting age against laryngeal dimensions and the ratio of laryngeal dimensions at different levels within the larynx.

Results: The authors measured transverse and AP laryngeal dimensions in 99 children, aged 2 months-13 yr. The relationship between the transverse and AP dimensions at all levels of the larynx did not change during development. Transverse and AP dimensions increased linearly with age at all levels of the larynx. In all children studied, the narrowest portion of the larynx was the transverse dimension at the level of the vocal cords. Transverse dimensions increased linearly in a caudad direction through the larynx (P < 0.001), while AP dimensions did not change relative to laryngeal level. The shape of the cricoid ring did not change throughout childhood.     

Kyphoplasty versus vertebroplasty to increase vertebral body height: a cadaveric study

PURPOSE: To prospectively compare the vertebral height restoration achieved with kyphoplasty and vertebroplasty in fresh cadavers by using multi-detector row computed tomography (CT). MATERIALS AND METHODS: Institutional review board approval was not required because the donors had registered in and consented to an anatomic gift program prior to their death. Thirty-seven vertebrae were harvested from four donated cadavers of elderly female individuals (mean age, 82 years; age range at death, 73-87 years). The vertebrae were dissected free of the surrounding muscles and imaged with multi-detector row CT. Compression fractures were induced, and the vertebrae were again imaged. The vertebrae were randomized to be treated with kyphoplasty (n = 19) or vertebroplasty (n = 18) and were then imaged at multi-detector row CT. The anterior, central, and posterior vertebral body heights and wedge angles were measured in the midsagittal plane of the reformatted images. The amount of cement injected was determined by weighing the vertebrae before and after treatment. The statistical significance of changes in vertebral body height, wedge angle, and weight with the two treatment techniques was evaluated with the independent t test or Mann-Whitney U test. RESULTS: The increase in vertebral height was greater with kyphoplasty than with vertebroplasty (5.1 mm vs 2.3 mm, respectively; P < .05). The original vertebral height was restored in 93% of vertebrae with kyphoplasty and in 82% with vertebroplasty (P < .05). There was a greater decrease in wedge angle with kyphoplasty than with vertebroplasty (3.1 degrees vs 1.6 degrees, respectively); however, this difference was not significant (P > .05). There was no significant difference in the amount of cement injected with kyphoplasty and vertebroplasty (P > .05). CONCLUSION: Kyphoplasty increased vertebral body height more than vertebroplasty in this model of acutely created fractures in fresh cadaver specimens.     

MR images mimic disc after discectomy

MRI of a 30-year-old woman 1 year after discectomy showed a residual disc-like tissue. The observation was initially confusing, but a close comparison of pre- and post-operative images suggested that the inferior wall of the anterior joint capsule had migrated superiorly after the removal of the disc and mimicked a residual disc on the follow-up MR images.     

Conspicuity of diffuse axonal injury lesions on diffusion-weighted MR imaging

OBJECTIVE: (1) To detect diffuse axonal injury (DAI) lesions by diffusion-weighted imaging (DWI), as compared with fluid-attenuated inversion recovery (FLAIR) imaging and (2) to evaluate hemorrhagic DAI lesions by b0 images obtained from DWI, as compared with gradient-echo (GRE) imaging. METHODS: We reviewed MR images of 36 patients with a diagnosis of DAI. MR imaging was performed 20 h to 14 days (mean, 3.7 days) after traumatic brain injury. We evaluated: (1) conspicuity of lesions on DWI and FLAIR and (2) conspicuity of hemorrhage in DAI lesions on b0 images and GRE imaging. RESULTS: DWI clearly depicted high-signal DAI lesions. The sensitivity of DWI to lesional conspicuity in DAI lesions was almost equal to that of FLAIR. The sensitivity of b0 images to identification of hemorrhagic DAI lesions was inferior to that of GRE. CONCLUSION: DWI is as useful as FLAIR in detecting DAI lesions. GRE imaging is still the superior tool for the evaluation of hemorrhagic DAI.