Choanae

Where are the choanae located and what do they bound?

The bony nasal cavity (Cavitas nasalis ossea) has a trapezoidal shape. It is divided along the midline by the bony nasal septum (Septum nasi osseum), on either side of which lie the posterior nasal apertures.

• Posterior boundary of the nasal cavity — represented directly by the choanae (choanae). For comparison, the anterior boundary of the nasal cavity is the piriform aperture (Apertura piriformis).
• Bony nasal septum (Septum nasi osseum) — divides the right and left halves of the nasal cavity. The septum is formed by the perpendicular plate of the ethmoid bone, the vomer (vomer), the nasal crest of the frontal bone, and the sphenoidal crest of the body of the sphenoid bone.

Topography on the external skull base

When viewing the skull from the inferior (basal) norm, the external skull base proper (Basis cranii externa) is distinguished. It is conventionally divided into an anterior smaller part (hard palate) and a posterior larger part.

• Anterior boundary of the external skull base — anteriorly (except for the hard palate region), the external skull base is bounded by the choanae (aperturae nasales posteriores).
• Communications of the skull base — through the choanae, the external skull base communicates freely with the nasal cavity. Posteriorly and laterally to the choanae, the base is bounded by anatomical structures of the temporal and occipital bones, and laterally it continues freely into the infratemporal fossa (Fossa infratemporalis).

What structures do the choanae communicate with?

Posterior to the nasal cavity lies the nasal part of the pharynx (Pars nasalis pharyngis), which extends from the pharyngeal vault to the soft palate.

• Connection with the nasal cavity — the nasopharynx communicates with the nasal cavity through the choanae (choanae).
• Adjacent structures of the nasopharynx — the mucosa of the nasal part of the pharynx is covered with ciliated epithelium. On the lateral wall of the nasopharynx are the pharyngeal opening of the auditory tube (Ostium pharyngeum tubae auditivae) and the torus tubarius (Torus tubarius), passing into the salpingopharyngeal fold (Plica salpingopharyngea). In the region of the vault lies the pharyngeal tonsil (Tonsilla pharyngealis).

Walls and nasal meatuses leading to the choanae

The bony nasal cavity has the following walls:

• Superior wall — formed by the nasal and frontal bones, the cribriform plate of the ethmoid bone, and the body of the sphenoid bone.
• Inferior wall — corresponds to the hard palate.
• Lateral wall — includes the ethmoidal labyrinth, the nasal conchae (superior, middle, inferior), and the medial plate of the pterygoid process of the sphenoid bone.

Between the nasal conchae and the septum, the common nasal meatus (Meatus nasi communis) is formed. The nasopharyngeal meatus (Meatus nasopharyngeus) leads into the region of the nasopharynx.

Choanae in the skull communication system

The external skull base, the anterior boundary of which is formed by the choanae, has additional communications and apertures. Along with the choanae, which provide connection with the nasal cavity, the following are present here:

• Free connection — with the infratemporal fossa (Fossa infratemporalis), which is bounded medially by the lateral plate of the pterygoid process.
• Pterygoid canal (Canalis pterygoideus) — connects the external skull base with the pterygopalatine fossa (Fossa pterygopalatina).
• Major apertures of the base — foramen magnum (Foramen magnum), jugular foramen (Foramen jugulare), lacerum foramen (Foramen lacerum), carotid canal (Canalis caroticus), and other structures.

Class and exam questions

What else to study on this topic

• Bony nasal cavity (Cavitas nasalis ossea)
• External cranial base (Basis cranii externa)
• Nasal part of the pharynx (Pars nasalis pharyngis)
• Bony nasal septum (Septum nasi osseum)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.