Orbital blow-out fracture
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Orbital blow-out fractures occur when there is a fracture of one of the walls of orbit but the orbital rim remains intact. Typically, this is caused by a direct blow to the central orbit from a fist or ball.
Epidemiology
The blow-out fracture is the commonest type of orbital fracture and is usually the result of trauma, often of sporting origin. This is reflected in the demographics and the fact that the commonest group of patients are young men.
Clinical presentation
Orbital blow-out fractures are usually the result of a direct blow to the orbit. This results in a sudden increase in the intraorbital pressure which in turn causes decompression by fracture of one or more of the bounding walls of the orbit.
The trauma is usually substantial, but presentation and diagnosis may sometimes delayed. This delay is usually due to intact orbital rim (by definition) and swelling making assessment of diplopia and extra-ocular movement difficult.
Associated clinical findings may include:
- enophthalmos: due to increased orbital volume
- diplopia: due to extra-ocular muscle entrapment
- orbital emphysema: especially when fracture is into an adjacent paranasal sinus
- malar region numbness: due to injury to the inferior orbital nerve
- hypoglobus.
Pathology
Different types of blow-out fracture
Blow-out fractures can occur through one or more of the walls of the orbit:
- inferior (floor)
- medial wall (lamina papyracea)
- superior (roof)
- lateral wall
Inferior blow-out fracture
Inferior blow-out fractures are the most common. Orbital fat prolapses into the maxillary sinus and may be joined by prolapse of the inferior rectus muscle. In children, the fracture may spring back into place (see trapdoor fracture). Most fractures occur in the floor posterior and medial to the infraorbital groove 5.
In approximately 50% of cases, inferior blow-out fractures are associated with fractures of the medial wall 4.
Medial blow-out fracture
Medial blow-out fractures are the second most common type, occurring through the lamina papyracea. Orbital fat and the medial rectus muscle may prolapse into the ethmoid air cells.
Superior blow-out fracture
Pure superior blow-out fractures (i.e. those without an associated orbital rim fracture) are uncommon. They are usually seen in patients with pneumatisation of the orbital roof 1,5. Fractures may only involve the sinus, the anterior cranial fossa (less common), or both sinus and anterior cranial fossa. In the latter, CSF leaks and meningitis may occur.
Lateral blow-out fracture
Lateral blow-out fractures are rare as the bone is thick and bounded by muscle. If fractures are present they are usually in the presence of orbital rim or significant craniofacial injuries.
Radiographic features
Plain radiograph
Radiographs no longer have a real role to play in the assessment of facial trauma. However, if they are obtained, the diagnosis of fractures involving the inferior or medial wall may be suspected by visualisation of fluid with the the maxillary sinus and ethmoidal air cells respectively 4. Orbital emphysema may also be visible. Under certain circumstances this may give a black eyebrow sign. Herniation of orbital fat inferiorly may give a "tear drop" sign.
CT
CT is the modality of choice for assessment of the facial skeleton, and does not require the administration of contrast. Ideally, thin slice volumetric scanning with 3-plane orthogonal reconstructions with both soft tissue and bone algorithm should be obtained.
In addition to evaluating the location and extent of the fracture, other features that need to be assessed and commented on include:
- presence of intra-orbital haemorrhage
- may result in stretching or compression of the optic nerve
- globe injury / rupture
- extraocular muscle entrapment
- suspected if there is an acute change in angle of the muscle 4
- prolapse of orbital fat
Treatment and prognosis
Indications for surgical repair include significant enophthalmos, significant diplopia, muscle entrapment, and large area fractures. The timing of surgery is a subject of debate, with many surgeons electing to allow swelling to subside prior to contemplating repair.
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