10.3 Maxillofacial, Mandible & TMJ CT

Why This Topic Matters on the ARRT CT Exam

This section closes out the Head subcategory with ARRT's final three named leaf items: maxillofacial bones, dedicated mandible, and temporomandibular joints (TMJs). Facial trauma classification (especially the Le Fort system) is one of the most heavily tested named-pattern topics in cross-sectional imaging, and the mandible and TMJ each require protocol decisions (panoramic reformats, dual mouth-position acquisition) that do not apply anywhere else in the Head cluster — making this content both trauma-heavy and technically distinct.

Core Terms and Technique

Maxillofacial CT (Facial Trauma Protocol)

Facial trauma CT is a thin-section (submillimeter), noncontrast axial helical acquisition spanning the entire facial skeleton (orbits through mandible), reconstructed with both bone and soft-tissue algorithms, then reformatted into coronal and sagittal planes plus 3D volume-rendered (VRT) images for surgical planning. Contrast is added only if a vascular injury (e.g., carotid or vertebral artery dissection from blunt neck/face trauma) is suspected.

Le Fort fracture classification describes three patterns of midface fracture, all unified by one requirement: a true Le Fort fracture must include a fracture through the pterygoid plates (bilaterally). Without pterygoid plate involvement, a fracture pattern that otherwise resembles a Le Fort is not classified as one.

Two related but distinct fracture patterns are commonly tested alongside Le Fort:

• Zygomaticomaxillary complex (ZMC) fracture (also called a "tripod" fracture) — separate from the Le Fort system — involves the zygomaticofrontal suture, zygomaticomaxillary buttress, zygomatic arch, and orbital floor.
• Naso-orbito-ethmoid (NOE) fracture — comminution of the central midface and medial orbital walls, placing the medial canthal tendon and nasolacrimal duct at risk.

Dedicated Mandible CT

The mandible is best conceptualized as a ring structure — like the bony pelvis — so a fracture at one site frequently has a second fracture elsewhere on the ring, and the technologist/radiologist should always look for a paired fracture. Dedicated mandible CT uses thin axial acquisition with curved (panoramic-style) reformats plus 3D VRT to unroll the ring-shaped bone into a single interpretable image. Common fracture sites include the parasymphysis, body, angle, ramus, and condyle. A classic tested pattern is the "guardsman fracture" — bilateral parasymphyseal plus bilateral condylar fractures — typically from a direct fall or blow onto the point of the chin.

TMJ CT

TMJ CT is technically unique in the Head cluster because it is acquired in two mouth positions for each side: closed-mouth (teeth together) and open-mouth (maximal opening, or as tolerated in trauma), using thin sections (roughly 1–2.5 mm) angled in an oblique sagittal plane perpendicular to the long axis of the condyle.

CT is the modality of choice for evaluating the bony components of the joint — condylar morphology, joint space narrowing, osteophytes, sclerosis, erosion, and true bony ankylosis. However, MRI remains the primary modality for evaluating the fibrocartilaginous disc position (anterior disc displacement with or without reduction) — a CT technologist must recognize when a clinical question about "the disc" actually requires an MRI referral rather than an additional CT mouth position.

Exam Scenario Walkthrough

A restrained driver in a high-speed motor vehicle collision undergoes facial trauma CT. The images show bilateral pterygoid plate fractures, fractures through the inferior orbital rims, and involvement of the nasal bones and medial orbital walls, sparing the zygomatic arches — a Le Fort II pattern. A second patient with an isolated blow to the chin shows bilateral parasymphyseal mandible fractures plus bilateral condylar fractures — the guardsman fracture pattern, prompting a careful search of the entire mandibular ring for any additional fracture. A third, non-trauma patient with chronic jaw pain and limited opening undergoes TMJ CT in both closed- and open-mouth positions; the open-mouth image shows the condyle failing to translate past the articular eminence, raising concern for ankylosis and prompting an MRI referral to evaluate disc position.

Takeaways

• A true Le Fort fracture requires bilateral pterygoid plate involvement; Le Fort I fractures the pyriform margin, Le Fort II the inferior orbital rim, and Le Fort III the zygomatic arch.
• ZMC ("tripod") fractures and NOE fractures are related but separate classification systems from Le Fort.
• The mandible behaves like a ring structure — always search for a second fracture when one mandible fracture is identified; the bilateral parasymphyseal-plus-condylar pattern is the classic "guardsman fracture."
• Dedicated mandible CT uses curved panoramic reformats to make the ring-shaped bone easier to interpret in a single image.
• TMJ CT is acquired in both closed- and open-mouth positions; CT excels at bony detail (condyle, joint space, ankylosis) while MRI remains primary for evaluating disc position.