Posterior Ethmoid Roof

From greek ethmos sieve is an unpaired bone in the skull that separates the nasal cavity from the brain.

Posterior ethmoid roof.

The ethmoid bone is one of the bones that make up the orbit of the eye. Onodi cells are important to identify preoperatively because the optic nerve traverses the roof of these cells. The ethmoid bone is a single midline bone that forms the roof and lateral walls of the upper nasal cavity the upper portion of the nasal septum and contributes to the medial wall of the orbit figure 7 11 and figure 7 12. The ethmoid bone ˈ ɛ θ m ɔɪ d.

Intracranially the ethmoidal canals open on the suture between the orbital part of the frontal bone and the cribriform plate. Using this same reference point the mean vertical distance to the natural sphenoid ostium sphenoid roof and sphenoid floor was 2 76 2 80 mm 12 18 3 20 mm and 5 94 2 94 mm respectively. An onodi cell is a posterior ethmoid cell that lies superior and or lateral to the sphenoid. The orbital opening of the ethmoidal canals are located at the junction of the roof and medial wall of the orbit along the frontoethmoid suture formed by the medial edge of the orbital plate of the frontal bone above and the perpendicular plate of the ethmoid below see fig.

The safest method of performing a complete ethmoidectomy is to remove the inferior anterior and posterior ethmoid cells until the sphenoid face is reached then identify the skull base at the posterior ethmoid or sphenoid sinus roof and dissect along the skull base from a posterior to anterior direction. The cubical bone is lightweight due to a spongy construction.