Facial Bones and Sinuses X-Ray

Plain radiography of the facial bones and paranasal sinuses images the nasal bones, orbits, maxillae, zygomatic arches, mandible and the maxillary, frontal, ethmoid and sphenoid sinuses.

The usual views are the occipitomental view at 15 and 30 degrees (Waters view, the best single film for the maxillary sinuses, orbital floors, zygomatic complex and maxillary walls), the occipitofrontal view (Caldwell, for the frontal and ethmoid sinuses and orbital rims), a lateral view (nasal bones, sphenoid and frontal sinuses, facial profile and fluid levels) and the submentovertical view (zygomatic arches and skull base).

For the mandible, the orthopantomogram (OPG, a panoramic film) with a posteroanterior mandible view is used, and for the nasal bones a lateral coned view. The effective dose is low (about 0.02 to 0.05 mSv for sinus and facial series, 0.01 to 0.03 mSv for an OPG).

CT has replaced plain films for most facial trauma and sinus disease, because it shows fractures, soft tissue injury, sinus anatomy and complications in one examination. Plain films remain useful for isolated mandibular injury (with an OPG), suspected zygomatic arch fracture, a screening look for foreign bodies in the orbit before MRI, and in low resource settings where CT is unavailable.

For rhinosinusitis, imaging is not needed in uncomplicated acute disease, which is clinical and mostly viral; opacification on plain films correlates poorly with symptoms and is found in many asymptomatic people and children with colds.

Indications. Facial trauma where CT is not available (suspected fracture of the zygoma, maxilla, orbit or mandible). Suspected mandibular fracture (OPG, with a second view because up to half of fractures are multiple). Suspected foreign body in the orbit or face. Suspected maxillary sinus air fluid level after trauma.

Selected cases of chronic sinus symptoms before CT, or to look for fluid levels in a patient who cannot have CT. Dental and jaw pathology (OPG). Not for uncomplicated acute sinusitis, headache, or a routine nasal fracture (nasal bone injuries are diagnosed clinically and treated by review of the swelling at 5 to 7 days).

Contraindications and precautions. No absolute contraindication. Pregnancy: low foetal dose, imaging when clinically required. Patients with suspected cervical spine injury must be immobilised, and the facial series is taken with the head in the position that the neck allows, with cross-table films. Remove dentures, earrings, hair clips and spectacles. Patients with suspected orbital or sinus fracture are told not to blow the nose, because this forces air into the orbit.

Preparation and technique. Sinus films are taken erect, to show air fluid levels, with a horizontal beam. Occipitomental views need the chin raised and mouth closed (a mouth open view shows the sphenoid sinus). For trauma, the patient is positioned as far as tolerance allows, and a supine film does not show fluid levels.

Normal appearances. Symmetrical translucent paranasal sinuses with thin smooth walls, a normal mucosa not visible, and no air fluid level. Intact orbital rims, with smooth continuous lines of the orbital floors, zygomaticomaxillary buttresses, zygomatic arches and mandibular outline.

The McGregor lines (smooth arcs along the zygomatic and maxillary outlines) can be traced on the occipitomental view. Frontal sinuses are absent or small in 5% of people and vary in size. Sinuses are not present in infants (maxillary at birth, ethmoid at birth, sphenoid at 3 to 5 years, frontal at 6 to 7 years and not fully developed until adolescence).

Interpretation.

• Sinusitis: mucosal thickening over 4 mm, air fluid level, or complete opacification of a sinus. Sinus opacification is non-specific (allergy, polyp, mucocele, tumour, haemorrhage after trauma). Features that suggest a complication (frontal bone osteomyelitis with a "moth eaten" appearance, orbital or intracranial extension) need CT.
• Sinus opacification with bone destruction or expansion: tumour (squamous carcinoma, inverted papilloma, lymphoma) or mucocele, to be confirmed by CT and biopsy.
• Maxillary and zygomatic fractures: the "tripod" fracture (zygomaticomaxillary complex) shows fractures of the lateral orbital rim at the zygomaticofrontal suture, the infraorbital rim and the zygomatic arch, with fluid or blood in the maxillary sinus. The McGregor lines on the occipitomental view help trace the fractures.
• Le Fort fractures: Le Fort I (horizontal maxillary fracture over the teeth), II (pyramidal, through the nasal bridge, medial orbit and infraorbital rim), III (craniofacial dysjunction through the zygomatic arches, orbits and nasal root). Films show opacified maxillary sinuses and disruption, but CT is needed for classification.
• Orbital blow out fracture: orbital floor defect with soft tissue prolapse into the maxillary sinus (teardrop or hanging drop sign), air fluid level in the maxillary sinus, orbital emphysema, and loss of the normal orbital floor line.
• Nasal bone fracture: lucent lines across the nasal bones on a lateral view, with soft tissue swelling and displacement; old fractures and nasal sutures may mimic.
• Mandibular fractures: OPG shows the angle, body, symphysis, condylar neck and ramus; two fractures are common (for example, body and contralateral condyle), so the entire mandible is checked. Dentoalveolar and temporomandibular joint injuries need dental views or CT.
• Foreign bodies: radio opaque material in the orbit or soft tissues; glass and metal are seen, wood and plastic are not.
• Jaw lesions on OPG: radiolucent cysts (dentigerous, odontogenic keratocyst, radicular), ameloblastoma (multilocular), and osteomyelitis.

Critical values and findings needing immediate action.

• Orbital floor fracture with diplopia, restricted upward gaze, or an oculocardiac reflex (bradycardia, vomiting, syncope, especially in children where a "trapdoor" fracture may entrap muscle): urgent ophthalmology or maxillofacial review and CT, with surgery within 24 to 48 hours.
• Retrobulbar haematoma (proptosis, pain, loss of vision, afferent pupillary defect): a clinical emergency needing immediate lateral canthotomy, without waiting for imaging.
• Le Fort II and III fractures or bilateral mandibular fractures with airway compromise or bleeding: airway management, haemorrhage control and urgent CT.
• Frontal sinus fracture with posterior wall involvement, cerebrospinal fluid leak or pneumocephalus: neurosurgical and maxillofacial review.
• Sinusitis with periorbital swelling, proptosis, visual change, severe headache, or neurological signs: urgent CT or MRI for orbital abscess, subperiosteal abscess, cavernous sinus thrombosis and intracranial extension, plus intravenous antibiotics.
• Open fracture or tooth loss with aspiration risk: examine airway, and obtain a chest film if teeth are missing.

Limitations and artefacts.

• Plain films have limited sensitivity for facial fractures (about 60 to 80% for zygomatic and orbital fractures), fail to show orbital contents, the ethmoids and the skull base, and cannot grade fractures, so CT is needed when management depends on detail.
• Sinus opacification and mucosal thickening correlate poorly with symptoms, and about one in three asymptomatic adults has incidental abnormalities on imaging.
• Supine films do not show air fluid levels, and a rotated film gives asymmetry that mimics opacity.
• Sutures, vascular channels, foramina, normal asymmetry and the lines of the frontal sinus septum mimic fractures. Comparison with the opposite side and clinical examination is essential.
• Young children have small or absent sinuses, and mucosal thickening is normal in many infants.
• Radiation dose is low, but repeated films do not replace a CT where one is needed.
• Dental artefacts (fillings, crowns, dentures) obscure details on the OPG.

Special groups.

• Children: avoid sinus films, which do not change management; imaging only for suspected complications (CT or MRI), and for facial trauma use ultrasound for the nasal bones or CT with a low dose technique.
• Pregnancy: low dose; imaging as needed.
• Elderly patients with falls: mandibular and zygomatic fractures are underdiagnosed; edentulous mandibles fracture at lower force.
• Patients with suspected non-accidental injury: facial and dental injuries are part of the skeletal survey.
• Regions: facial fractures from road traffic injuries, assault and firearm injuries are frequent, and plain films with an OPG are the main imaging in many centres; chronic sinus disease from fungal infection and noma related jaw destruction occur in some regions.

Follow up tests. CT face and sinuses with bone windows and three dimensional reconstruction for fractures and complex sinus disease, CT or MRI orbits and brain for complications, MRI for suspected tumour, dental review and cone beam CT, ophthalmic assessment (visual acuity, eye movements, intraocular pressure), nasal endoscopy, allergy testing, and biopsy for suspected tumours.