Learning Objective: At the end of this session, the learner should be able to describe the bones, boundaries, contents, foramina, and clinical relevance of the anterior cranial fossa.

The floor of the cranial cavity is divided into three distinct depressions — the anterior, middle, and posterior cranial fossae. Each fossa supports a specific part of the brain. The anterior cranial fossa is the most shallow and superior of the three and lies over the nasal and orbital cavities. It houses the anteroinferior portions of the frontal lobes of the brain.

Borders

The anterior cranial fossa is formed by three bones — the frontal, ethmoid, and sphenoid bones — and is bounded as follows:

• Anteriorly and laterally: by the inner surface of the frontal bone.
• Posteriorly and medially: by the limbus of the sphenoid bone, forming the anterior border of the prechiasmatic sulcus (a groove between the optic canals).
• Posteriorly and laterally: by the lesser wings of the sphenoid bone, which project from its central body.
• Floor: formed by the frontal bone, ethmoid bone, and the anterior parts of the body and lesser wings of the sphenoid.

Contents and Bony Landmarks

Several key bony features and neurovascular structures are present in the anterior cranial fossa:

• Frontal Crest: A midline ridge of the frontal bone; attachment site for the falx cerebri (a dural fold separating the cerebral hemispheres).
• Crista Galli (Ethmoid Bone): A prominent upward projection, also providing attachment for the falx cerebri.
• Cribriform Plate (Ethmoid Bone): Situated on either side of the crista galli; supports the olfactory bulbs and transmits olfactory nerve fibers (CN I) through its tiny foramina.
• Lesser Wings of Sphenoid: Form the posterior limit of the fossa and end in anterior clinoid processes, which anchor the tentorium cerebelli (the dural fold separating the cerebrum from the cerebellum).

Activity:

Foramina

The ethmoid bone contains the primary foramina of the anterior cranial fossa:

• Cribriform foramina: Numerous tiny openings in the cribriform plate transmitting olfactory nerve fibers (CN I).
• Anterior ethmoidal foramen: Transmits the anterior ethmoidal artery, vein, and nerve.
• Posterior ethmoidal foramen: Transmits the posterior ethmoidal artery, vein, and nerve.

Clinical Relevance

Fracture of the Cribriform Plate: The cribriform plate of the ethmoid is thin and fragile, making it vulnerable to fractures—especially from trauma to the nasal region.

Activity:

Key Points

• The anterior cranial fossa is the most superior and shallowest of the cranial fossae.
• Formed by the frontal, ethmoid, and sphenoid bones.
• Contains important landmarks such as the frontal crest, crista galli, and the cribriform plate.
• Transmits the olfactory nerve (CN I) through the cribriform foramina.
• Fracture of the cribriform plate can lead to anosmia and CSF rhinorrhoea.

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