Bones - Ethmoid Bone

Question 1

Anatomical structure of the ethmoid bone

Surfaces contributing to orbit?

Surfaces contributing to the nasal cavity?

Bony landmarks?

Answer 1

1) Orbital plate - contributes to the medial wall of the orbit.
2) Medial sheet - represents the superior aspect of the lateral wall of the nasal cavity, from which the superior and middle conchae extend into the nasal cavity.

Superior surface - cribiform plate forms the roof of the nasal cavity - olfactory nerve fibres pierces through this structure from the olfactory bulb to provide smell.

1) Superior nasal conchae
2) Middle nasal conchae
3) Crista galli - attachment point for the falx cerebri that separates the cerebrum into their hemispheres.

Question 2

Clinical relevance: ethmoid fractures

Aetiology?

Signs and symptoms?

Answer 2

Aetiology - facial trauma - RTA or fall from a height

Signs and symptoms:
1) Fracture of cribiform plate - branches of the olfactory bulb may be sheared, causing anosmia (loss of smell).

2) Fracture of the labyrinth - allows communication between the nasal cavity and the orbit. It is possible for air to enter the orbit and cause orbital emphysema.

Question 3

Clinical relevance: CSF rhinnorhea

Answer 3

This occurs when the cribiform plate is fractured - this allows communication between the CNS and the nasal cavity, allowing CSF to drain out of the nasal cavity.

Leaks stop by itself or otherwise surgery may be required.

Spontaneous CSF rhinnorhea may be due to congenital or acquired defects.