The anterior cranial fossa is the most shallow and superior of the three cranial fossae. It is located superiorly above the nasal and orbital cavities and accommodates the anteroinferior portions of the frontal lobes of the brain. In this article, we shall look at the borders, contents and clinical correlations of the anterior cranial fossa.
The anterior cranial fossa is composed of three bones: the frontal bone, ethmoid bone, and sphenoid bone. It is bounded anteriorly and laterally by the inner surface of the frontal bone, posteriorly and medially by the limbus of the sphenoid bone, and posteriorly and laterally by the lesser wings of the sphenoid bone.
The limbus of the sphenoid bone is a bony ridge that forms the anterior border of the prechiasmatic sulcus - a groove running between the right and left optic canals. The lesser wings of the sphenoid bone are two triangular projections of bone that arise from the central sphenoid body. The floor of the anterior cranial fossa is composed of the frontal bone, ethmoid bone, and the anterior aspects of the body and lesser wings of the sphenoid bone.
The anterior cranial fossa has several bony landmarks. The frontal bone is marked in the midline by a body ridge known as the frontal crest. This projects upwards and serves as an attachment site for the falx cerebri – a sheet of dura mater that divides the two cerebral hemispheres.
In the midline of the ethmoid bone, the crista galli (Latin for cock’s comb) is situated. This is an upwards projection of bone which also serves as an attachment point for the falx cerebri. On either side of the crista galli is the cribriform plate which supports the olfactory bulb and has numerous foramina that transmit vessels and nerves.
The anterior aspect of the sphenoid bone is located within the anterior cranial fossa. From the central body of the sphenoid bone, the lesser wings arise. The rounded ends of the lesser wings are known as the anterior clinoid processes and provide an area of attachment for the tentorium cerebelli – a sheet of dura mater that divides the cerebrum from the cerebellum. The lesser wings of the sphenoid bone also separate the anterior and middle cranial fossae.
The ethmoid bone contains the main foramina of the anterior cranial fossa. The cribriform plate is a sheet of bone seen either side of the crista galli which contains numerous small foramina that transmit olfactory nerve fibres (CN I) into the nasal cavity. It also contains two larger foramen – the anterior ethmoidal foramen and posterior ethmoidal foramen.
The anterior ethmoidal foramen transmits the anterior ethmoidal artery, nerve and vein, while the posterior ethmoidal foramen transmits the posterior ethmoidal artery, nerve and vein.
The cribriform plate of the ethmoid is the thinnest part of the anterior cranial fossa, and therefore most likely to fracture. There are two major consequences of a fractured cribriform plate: anosmia and cerebrospinal fluid (CSF) rhinorrhoea.
Anosmia is the loss of the sense of smell due to the shearing off of the olfactory nerve fibres which run through the cribriform plate. CSF rhinorrhoea is the leakage of CSF into the nasal cavity which occurs when the fragments of bone tear the meningeal coverings of the brain. This is visible as a clear fluid.
The Anterior Cranial Fossa is an anatomical region located at the base of the skull. It is formed by the union of four borders, the frontal, ethmoidal, sphenoidal, and the cribriform plate. This area is of great relevance clinically, as it contains important structures such as the falx cerebri, crista galli, olfactory bulb, and the anterior and posterior ethmoidal foramina.
The frontal crest, an elevation of the cribriform plate, divides the fossa in two and creates a groove where the anterior ethmoidal artery runs. This crest is marked by a body ridge in the midline and projects upwards to act as a point of attachment for the falx cerebri, a sheet of the dura mater which divides the two cerebral hemispheres.
On the midline of the ethmoidal bone lies the crista galli (Latin for cock's comb), which is a prominent upward projection of bone that also serves to attach the falx cerebri. On either side of the crista galli, one finds the cribriform plate, a sheet of bone that supports the olfactory bulb and has numerous foramina that transmit vessels and nerves. It is considered to be the thinnest part of the anterior cranial fossa and, as such, is most likely to sustain fractures.
Of the four borders of the Anterior Cranial Fossa, the ethmoid is the one that contains the main foramina, openings that transmit vessels and nerves. Due to this anatomy, the cribriform plate is home to numerous small foramina that transmit olfactory nerve fibres (CN I), as well as two larger foramina: the anterior and posterior ethmoidal foramina. The former transmits the anterior ethmoidal artery, nerve and vein; the latter transmits the posterior ethmoidal artery, nerve and vein.
Clinically, fractures of the cribriform plate can cause anosmia due to disruption of the olfactory pathways, or cerebrospinal fluid (CSF) rhinorrhoea due to tearing of the dura mater. Anosmia is the loss of the sense of smell as a result of 'shearing' of the olfactory nerve fibres, while CSF rhinorrhoea is the leakage of cerebrospinal fluid into the nasal cavity, visible as a clear fluid.
Identifying the anatomy of the Anterior Cranial Fossa and understanding its clinical relevance is important for assessing and treating skull-related injuries. It is of particular importance when it comes to fractures of the cribriform plate, as they can result in serious complications such as anosmia and CSF rhinorrhoea.
