What is the Sphenoid Bone?

The bat-shaped sphenoid bone sits at the base of the skull, with the wings comprising part of the bony orbit or eye socket on each side. Located in the central body of the sphenoid bone, the saddle-shaped concavity known as the sella turcica houses the pituitary gland. Extending from each side of the body are the greater wings of the sphenoid bone, which curve in a superior and lateral direction to form part of the orbital floor. The lesser wings of the sphenoid bone also spread outward, forming the posterior portion of the orbital roof on each side. Several notable arteries, veins, and nerves penetrate the greater and lesser wings of the sphenoid to enter and leave the orbits.

Piercing the lesser wings of the sphenoid, the optic canals allow passage of the optic nerves from the back of each eye to enter the brain and cross at the optic chiasma above to the pituitary gland. A cleft between the greater and lesser wings of the sphenoid, the superior orbital fissure transmits several critical structures that pass between the orbit and the brain. These structures include the oculomotor, trochlear, and abducens nerves, which provide the nerve supply to the muscles that move each eye. In addition, the fissure contains the ophthalmic division of the trigeminal nerve, which supplies sensation to the upper face, and the superior and inferior ophthalmic veins, which drain blood from the eye and orbit. Fractures of the eye socket, particularly involving the orbital floor, can potentially damage these structures as they traverse the fissure.

The greater wings of the sphenoid bone also contain holes or foramina that bear nerves for sensation of the lower face and the teeth. Formed by the sphenoid bone and the maxilla, the inferior orbital fissure provides passage for the maxillary nerve, giving sensation to the middle face and upper teeth, and the branches of the pterygopalatine ganglion, which supply sensation to the sinuses, nasal cavity, gums, and throat. The extremely concave surface of each greater wing makes up part of the middle fossa of the skull, which houses the temporal lobes of the brain. Pterygoid processes descend bilaterally in a perpendicular direction from the junctions of the body and the greater wings. Each process consists of medial and lateral plates.

A sphenoid wing meningioma is a benign tumor involving the tissue that lines the brain near the sphenoid bone. Meningiomas occur most often in females over the age of 50. Symptoms of sphenoid wing meningioma include loss of vision, loss of color vision, pupil abnormalities, and visual field defects. In addition, a patient with an advanced tumor may experience lid swelling, bulging of the eye, and double vision. Treatment, depending on the size and location of the tumor, may include gamma knife radiation, external beam radiation, or microsurgery.