ethmoidal

Ethmoidal refers to the ethmoid bone, a light, spongy bone located between the nasal cavity and the orbits. It forms part of the anterior cranial floor, the medial wall of the orbits, and contributes to the nasal septum and the upper airway.

Anatomy: The ethmoid consists of a horizontal perforated cribriform plate, a perpendicular plate that forms part of the nasal septum, and lateral masses that harbor the ethmoidal air cells. The lateral masses also give rise to the superior and middle nasal conchae.

Ethmoidal air cells: The ethmoidal labyrinth contains numerous small air-filled cells that communicate with the nasal cavity. They drain anteriorly and medially into the middle meatus via the ethmoidal ostia, and their mucosa is supplied by branches of the ophthalmic nerve and vessels.

Vascular and neural supply: The anterior and posterior ethmoidal arteries originate from the ophthalmic artery and enter the ethmoid region through the respective ethmoidal foramina. The anterior and posterior ethmoidal nerves, branches of the nasociliary nerve (CN V1), supply the mucosa of the ethmoid and adjacent nasal cavity. The cribriform plate transmits olfactory nerve fibers (CN I).

Clinical relevance: The ethmoid bones are relatively fragile; fractures of the ethmoid region can involve the cribriform plate, increasing the risk of cerebrospinal fluid rhinorrhea and injury to olfactory nerves. Ethmoidal sinusitis is common and can spread to adjacent cavities or the orbit. Traumatic disruption of the lamina papyracea may cause orbital complications.