Sphenoid Wing Dysplasia

What sphenoid wing dysplasia is

The sphenoid bone sits in the middle of the skull base. Its two "greater wings" form much of the back and side walls of each eye socket (orbit) and separate the orbit from the middle cranial fossa, the space that holds the temporal lobe of the brain.

In sphenoid wing dysplasia, part of the greater wing is thin, malformed or missing. Without that bony wall:

• The coverings of the brain (meninges), spinal fluid and sometimes part of the temporal lobe can bulge into the back of the eye socket.
• Brain pulsations are transmitted to the eye, which can pulse in time with the heartbeat (pulsatile exophthalmos).
• The orbit and the middle cranial fossa often enlarge.

It is usually on one side and can be present at birth or develop and progress during childhood.

Link with neurofibromatosis type 1

Neurofibromatosis type 1 is a common genetic condition that affects about 1 in 3,000 people. It causes café-au-lait spots, freckling in the armpits and groin, nerve tumors called neurofibromas, and bone problems. Sphenoid wing dysplasia is one of the distinctive bone lesions listed in the NF1 diagnostic criteria.

It frequently occurs together with an orbital or periorbital plexiform neurofibroma, a large, soft nerve sheath tumor of the eyelid, temple and orbit. Experts debate whether the tumor contributes to the bone defect or whether both arise together, but the combination tends to progress.

Rarely, sphenoid dysplasia occurs without NF1.

Symptoms and signs

• Eye position changes: a bulging eye (proptosis) or, less often, a sunken eye (enophthalmos) on one side.
• Pulsation of the eye that may be visible or felt.
• Facial asymmetry: a fuller or hollow temple, uneven eye level.
• A droopy, thickened upper eyelid with an S-shaped outline, when a plexiform neurofibroma is present.
• Vision problems: blurred or double vision, a lazy eye (amblyopia) in children, or squint.
• Eye surface damage if the eyelids cannot close over a bulging eye.
• Glaucoma and enlargement of the eye in some children with eyelid plexiform neurofibromas.

Many people have only mild asymmetry and good vision.

Diagnosis

• Eye examination: vision, eye position, eye movements, eyelid closure, eye pressure and the optic nerve, often by a pediatric or oculoplastic ophthalmologist.
• CT scan with 3D reconstruction: best for showing the bone defect, the size of the orbit and the middle cranial fossa. On plain X-ray, the missing wing can produce an "empty" or "bare" orbit sign.
• MRI: shows the brain, the bulge of meninges or temporal lobe into the orbit, and any plexiform neurofibroma or optic pathway glioma.
• Genetic testing for NF1 if not already diagnosed.

Other conditions that can cause one-sided eye bulging or bony changes include thyroid eye disease, tumors, fibrous dysplasia and an orbital fracture, which imaging helps rule out.

Treatment

There is no single standard approach. Care is usually planned by a multidisciplinary team including neurosurgery, craniofacial or oculoplastic surgery, ophthalmology and an NF1 specialist.

Monitoring and eye care

• Regular eye exams, especially in children, to detect amblyopia, glaucoma and vision loss early.
• Glasses and patching therapy for a lazy eye.
• Lubricating drops and ointments, or eyelid surgery, to protect the cornea.

Surgery

Surgery is considered when the eye position is worsening, vision is threatened, or appearance is significantly affected:

• Orbital wall reconstruction: the defect is closed with bone grafts (often from the skull or ribs), titanium mesh or other implants to separate the brain from the orbit and reposition the eye.
• Debulking of plexiform neurofibroma from the eyelid and orbit.
• Eyelid and facial reconstruction.

Reconstruction is technically challenging, and the defect can recur as bone around the repair may continue to resorb. Long-term follow-up is needed.

Medicines for plexiform neurofibromas

MEK inhibitors, selumetinib and mirdametinib, are approved for symptomatic plexiform neurofibromas that cannot be fully removed. They can shrink tumors around the orbit in many patients, which may help appearance and eye function, though they do not repair the bone.

Outlook

The course varies. Some people have a stable, mild defect throughout life. Others, particularly those with an associated plexiform neurofibroma, have progressive bulging and vision problems that need repeated treatment. Early, regular eye care is the most important factor in protecting sight.

Frequently asked questions

What is sphenoid wing dysplasia?

It is a malformation of the sphenoid bone, which forms the back wall of the eye socket. Part of the bone is thin or missing, so brain coverings and fluid can push into the socket. The eye may bulge, sink or pulse. It is most often a feature of neurofibromatosis type 1.

Is sphenoid wing dysplasia always caused by NF1?

Almost always. It is one of the characteristic bone lesions of neurofibromatosis type 1 and is included in its diagnostic criteria. Rare cases occur without NF1. Anyone found to have it should be examined for other NF1 features and may be offered genetic testing.

Why does the eye pulsate in sphenoid wing dysplasia?

Because the bony wall between the eye socket and the brain is missing, the normal pulsations of the brain and its fluid with each heartbeat are transmitted directly to the eye. This is called pulsatile exophthalmos and is a classic sign of the condition.

Does sphenoid wing dysplasia get worse?

It can. In some people it stays stable, but it may progress during childhood, especially when a plexiform neurofibroma is present around the eye. Regular eye exams and periodic imaging help detect changes early so treatment can be planned.

Can sphenoid wing dysplasia be fixed?

Surgeons can reconstruct the eye socket wall with bone grafts or titanium mesh and reposition the eye. Results are often good, but the repair can be difficult and the defect sometimes returns. Treatment of any plexiform neurofibroma, including MEK inhibitor medicines, is often part of the plan.