Submentovertex View
Dental Radiology · Extraoral Radiography
TL;DR
The submentovertex (SMV) view is an extraoral skull projection providing an axial (inferior-to-superior) cross-section of the skull base — the only conventional plain film technique capable of projecting both zygomatic arches free of superimposition.
- The submentovertex (SMV) view — also called the base of skull view, axial skull view, or “jug-handle” view — is an extraoral skull projection in which the beam is directed vertically upward from beneath the patient’s extended chin toward the vertex of the skull
- The patient hyperextends the neck so the skull vertex is closest to the receptor and the orbitomeatal line (OML) is as close to parallel with the receptor surface as possible; the beam enters below the chin (submental) and exits at the vertex
- Primary indications: zygomatic arch fractures (the most common use in dental/maxillofacial practice), assessment of the sphenoid sinuses, base of skull, and condylar heads in the axial plane, and assessment of facial width/arch symmetry
- The SMV view provides an axial (top-down) perspective of the skull base that no other conventional plain film projection can offer — it is especially valuable for detecting lateral “blow-out” fractures of the zygomatic arch that appear normal on a standard PA view
- It requires significant neck hyperextension, which may be contraindicated in patients with cervical spine injury — clinical clearance is required before positioning
Key Facts
What Is It?
The submentovertex (SMV) view is an extraoral radiograph of the skull taken with the patient in marked neck hyperextension, the X-ray tube directed vertically upward from below the chin, and the image receptor positioned at the vertex (top) of the head. The resulting image provides a unique axial (inferior-to-superior) cross-section of the skull base, revealing structures including the zygomatic arches, sphenoid sinuses, posterior wall of the maxillary sinuses, mandibular condyles, and the base of the skull.
The name is anatomically descriptive: “sub” (below) + “mento” (chin) + “vertex” (top of skull) — the beam travels from below the chin to the vertex. It is sometimes called the “jug-handle view” because the bilateral zygomatic arches appear as handles projecting symmetrically from the sides of the image.
Why It Matters
The SMV view occupies a unique position in the plain film skull radiograph repertoire: it is the only conventional projection that images the skull base in the axial plane. All other standard skull projections — PA, lateral, Waters’, Reverse Towne’s — are obtained in coronal or sagittal orientations. The axial perspective of the SMV is irreplaceable for assessing lateral arch fractures and evaluating cranial base symmetry.
Clinical Relevance
- Zygomatic arch fractures: The zygomatic arch is a thin, curved bone highly susceptible to direct lateral trauma. When fractured, it typically shows a tripod or V-shaped deformity best seen in the axial plane. Standard PA skull and Waters’ views may miss subtle zygomatic arch fractures because the arch is superimposed on other structures in those projections. The SMV view shows both arches in full projection, free of superimposition.
- Facial symmetry: The SMV view provides a true axial view of facial width — both zygomatic arches, condyles, and the base of the skull are visible simultaneously, allowing comparison of left-right symmetry.
- Sphenoid sinus assessment: The sphenoid sinuses are visible as bilateral air-filled spaces in the posterior cranial base — useful for detecting sphenoid sinusitis, masses, or involvement in posterior facial trauma.
- Condylar position: The condylar heads can be assessed in the axial plane — useful when medial/lateral displacement has occurred and cannot be fully characterised on the Reverse Towne’s view.
- INBDE relevance: The SMV view, its positioning technique, structures visible, and indications are tested as part of the extraoral radiography curriculum.
Technique and Positioning
Correct patient positioning is the most critical determinant of image quality in the SMV view. The degree of neck hyperextension directly controls how “axial” the resulting projection is.
- Explain the procedure to the patient and confirm the absence of contraindications (cervical spine injury, severe arthritis, inability to hyperextend neck)
- The patient sits or stands with their back to the X-ray unit (or the unit positioned behind and below)
- The patient hyperextends the neck as far as possible — the chin is raised maximally, and the top (vertex) of the skull is positioned closest to the receptor
- The image receptor is placed horizontally at the vertex of the skull (the patient essentially rests their head against the receptor)
- Ideally, the orbitomeatal line (OML — outer canthus of eye to centre of EAM) should be as close to parallel with the receptor as possible — with the OML parallel, the condylar heads are projected without distortion
- The X-ray tube is positioned below the patient’s extended chin, directed vertically upward
- The central ray passes from submental to vertex — straight upward through the skull base
- The midsagittal plane must be perpendicular to and centred on the receptor to ensure bilateral symmetry
- Expose; typical settings: 75–85 kVp; mAs sufficient for skull base penetration (higher than standard skull views due to bone density at the base)
Modification for Patients with Limited Neck Extension
If the patient cannot fully hyperextend, a partial SMV can still provide useful information. The degree of neck extension determines how “axial” the final view is. When full extension is impossible, the clinician should document the limitation and interpret the image accordingly, recognising that structures may be projected with greater obliquity than intended.
Alternative: CBCT provides the axial view without any positional demands and is increasingly the preferred modality in patients where neck hyperextension is limited or contraindicated.
Radiographic Anatomy Visible on the SMV View
The SMV provides an axial view — structures are projected as if looking down through the top of the skull. The image resembles a cross-section through the skull base. The hallmark appearance is the bilateral zygomatic arches projecting laterally like the handles of a jug — giving the view its informal name.
| Structure | Radiographic Appearance | Clinical Significance |
|---|---|---|
| Zygomatic arches (bilateral) | Curved radiopaque arcs projecting laterally — the “jug handles” | Fractures appear as V-shaped deformity, angulation, or discontinuity |
| Mandibular condyles | Oval/rounded radiopaque structures posterior to rami | Axial condylar position; medial/lateral displacement |
| Mandibular rami | Broad radiopaque structures between condyles and body | Ramus fractures; asymmetry |
| Sphenoid sinuses | Paired radiolucent air spaces centrally in posterior cranial base | Sinusitis; tumour; trauma involvement |
| Posterior maxillary sinus wall | Curved posterior wall visible in axial projection | Posterior wall fractures (rare but serious — can involve pterygoid plates) |
| Foramen ovale and spinosum | Small foramina in sphenoid bone | Visible in good-quality SMV; base of skull pathology |
| Nasal septum | Midline structure | Deviation; asymmetry |
| Hard palate (anterior) | Radiopaque arch in anterior image | Anatomical reference |
| Anterior arch of atlas (C1) | Radiopaque ring visible in very extended views | Cervical spine reference; confirms adequate extension |
What the SMV Does NOT Show Well
- Teeth and alveolar bone (not in the primary projection field)
- Mandibular body and symphysis
- Orbital floor (Waters’ view is better)
- Frontal sinuses (PA view or Waters’ view)
- Fine intra-articular TMJ detail
Clinical Applications
Zygomatic Arch Fractures — Primary Application
The zygomatic arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. It is vulnerable to direct blunt trauma (assault, falls, sports injuries) because of its lateral prominence and relative thinness.
Fracture patterns: Most commonly a tripod/tripartite pattern (zygomatic arch plus two other zygomatic sutures) or an isolated arch fracture. On the SMV view, a fractured arch appears as inward buckling or angulation on the affected side, often forming a characteristic V-shape — two fracture lines with the apex pointing medially toward the infratemporal fossa.
The medially displaced arch can impinge on the temporalis muscle and coronoid process of the mandible, causing restricted mouth opening (trismus). This clinical sign, combined with the SMV radiographic finding, confirms the diagnosis.
Treatment: If there is no trismus and no cosmetic deformity — conservative management with observation. If the arch is depressed and causing trismus or unacceptable cosmetic deformity — surgical elevation is required. The classic approach is the Gillies’ technique (temporal approach): an incision within the hairline provides access to the temporal fossa, and an elevator is passed beneath the temporalis fascia to elevate the depressed arch.
| View | Shows Zygomatic Arch? | Shows Orbital Floor? | Shows Sinus? | Best For |
|---|---|---|---|---|
| SMV | Best view for arch (axial) | No | Posterior wall | Isolated zygomatic arch fractures |
| Waters’ view | Yes (body of zygoma, not arch) | Best view | Yes (frontal) | Orbital floor blowout; maxillary sinus |
| PA skull | Partially | Limited | Frontal sinus | Facial width asymmetry |
| Panoramic (OPG) | No | No | Partial | Dental/mandibular survey |
| Reverse Towne’s | No | No | No | Condylar fractures |
| CBCT | Excellent (3D) | Excellent | Excellent | Complex zygomatic fractures, surgical planning |
Clinical Considerations
- Contraindications: Cervical spine injury (most important), severe kyphosis or arthritic cervical spine, patient inability to cooperate with neck hyperextension, recent neck surgery. Always screen for these before positioning. In any patient presenting following head or facial trauma, assume cervical spine involvement until proven otherwise.
- High kVp requirement: The skull base is one of the densest regions of the body radiographically. Higher kVp (75–85 kVp) and increased mAs compared to bitewing or periapical exposures are required for adequate penetration and diagnostically acceptable image density.
- Dose: The SMV delivers a relatively higher dose compared to intraoral radiographs due to the skull base being in the primary beam. The lens of the eye, parotid glands, and thyroid receive measurable dose. Use thyroid collar and lead apron; ensure correct horizontal centring to avoid unnecessary repeat exposures.
- CBCT as alternative: When CBCT is available, it provides superior axial and multiplanar views of the zygomatic arch and skull base at doses comparable to or less than a full skull series, and without the positioning demands of the SMV. The clinical scenario determines which is appropriate — in a stable patient, CBCT is often preferred; in a setting where CBCT is unavailable, the SMV remains the standard plain film technique.
- Artefacts: Jewellery (earrings, necklaces) must be removed before exposure — they produce radiopaque artefacts in the field of view and can obscure the zygomatic arch or other critical structures. Dental restorations in the molar region may also produce minor artefacts but are typically not in the primary plane of interest.
Common Mistakes & Misconceptions
The SMV view is a less frequently performed projection, which means misconceptions about its technique, indications, and interpretation are relatively common in exam settings.
-
Misconception: “The SMV view is the same as the Waters’ view.”
Correction: The SMV directs the beam vertically from below the chin to the skull vertex — providing an axial (inferior-to-superior) view of the skull base. The Waters’ view is a posteroanterior projection with the head tilted back approximately 45°, primarily designed to project the maxillary sinuses and orbital floors clear of the petrous ridges. They are completely different projections with different patient positions, beam angles, and indications. -
Misconception: “Zygomatic arch fractures are always visible on the panoramic radiograph.”
Correction: Panoramic radiographs do not image the zygomatic arch well. The arch lies outside the focal trough of the panoramic machine, and isolated zygomatic arch fractures are regularly missed on a panoramic. The SMV view is the dedicated plain film projection for the zygomatic arch. -
Misconception: “The SMV view can be performed on any trauma patient.”
Correction: The SMV view requires full neck hyperextension. In any patient with facial or head trauma, cervical spine injury must be excluded before attempting this position. Forcing a patient with an unstable cervical fracture into SMV hyperextension is a potentially fatal positioning error. The SMV view is absolutely contraindicated until the cervical spine is cleared. -
Misconception: “A symmetric appearance of both zygomatic arches on the SMV means no fracture has occurred.”
Correction: Incomplete fractures, non-displaced hairline fractures, or bilateral symmetric fractures can appear normal or nearly normal on the SMV view. Clinical findings (tenderness, trismus, palpable step deformity) combined with CBCT are needed for complete fracture exclusion in high-suspicion cases. -
Misconception: “The SMV view and the Reverse Towne’s view are interchangeable for condylar assessment.”
Correction: The SMV provides an axial view of condylar position (showing medial/lateral displacement from above). The Reverse Towne’s provides a posteroanterior view showing condylar height and neck fractures. They provide complementary information and are not interchangeable — each answers a different diagnostic question about the condyle.
Related Topics
The SMV view is best understood in the context of the full extraoral skull radiograph series and facial trauma imaging.
References & Sources
The following foundational texts and peer-reviewed sources inform this article.
- White SC & Pharoah MJ, 2014. Oral Radiology: Principles and Interpretation. 7th ed. Elsevier Mosby.
- Whaites E & Drage N, 2013. Essentials of Dental Radiography and Radiology. 5th ed. Churchill Livingstone.
- Kaeppler G, 2013. Application of cone beam computed tomography in dental and maxillofacial radiology. Clinical Oral Investigations, 17(Suppl 1):S13–S26.
- Ellis E & Zide MF, 2006. Surgical Approaches to the Facial Skeleton. 2nd ed. Lippincott Williams & Wilkins.
- Langland OE, Langlais RP & Preece JW, 2002. Principles of Dental Imaging. 2nd ed. Lippincott Williams & Wilkins.
Summary
The submentovertex view is the definitive plain film technique for axial skull base imaging. Its unique beam direction — vertically upward from below the chin to the skull vertex — produces an axial cross-section of the skull base that is unobtainable with any other conventional plain film projection. The bilateral zygomatic arches, sphenoid sinuses, mandibular condyles, and posterior maxillary sinus walls are all projected in the axial plane, making the SMV indispensable for detecting zygomatic arch fractures, evaluating axial condylar position, and assessing cranial base symmetry.
The view’s principal limitation is its requirement for full neck hyperextension — a position that is absolutely contraindicated in patients with uncleared cervical spine injury. Careful pre-exposure patient screening for cervical pathology is mandatory. Where CBCT is available, it increasingly replaces the SMV view for complex facial trauma and surgical planning, offering superior multiplanar information without positional demands. Nevertheless, the SMV remains an important technique in settings where CBCT is unavailable and in the examination of stable patients with suspected isolated zygomatic arch pathology.
Key Takeaways
- Unique axial projection: The SMV view directs the beam vertically upward from below the chin to the skull vertex — providing an axial cross-sectional view of the skull base that no other conventional plain film projection can replicate.
- Zygomatic arch fractures: The SMV is the only conventional plain film projection that shows both zygomatic arches in their full axial extent, free of superimposition — making it the first-line plain film for suspected isolated arch fractures.
- The jug-handle sign: The “jug-handle” appearance of the bilateral zygomatic arches is the hallmark of a well-positioned SMV view; unilateral V-shaped deformity or medial buckling indicates a depressed arch fracture.
- Cervical spine contraindication: CONTRAINDICATED in patients with uncleared cervical spine injury — neck hyperextension in a patient with an unstable cervical spine fracture is a potentially fatal positioning error. Always screen before positioning.
- CBCT as alternative: CBCT provides equivalent (and superior) axial information without positioning demands and is increasingly preferred when available, especially in trauma settings or when the patient cannot hyperextend the neck.
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