A foramen (pl. foramina) is an opening that allows the passage of structures from one region to another. These openings are collectively referred to as the cranial foramina, and are located in the skull base. In this article, we shall look at some of the major cranial foramina, and the structures that pass through them.
The foramina of the skull are most commonly considered in the context of the cranial nerves. In this section, we will discuss the foramina that transmit cranial nerves.
The cribriform foramina refer to numerous perforations in the cribriform plate of the ethmoid bone. These foramina transmit the olfactory nerve (CN I) and its branches, known as the anterior ethmoidal nerves. These nerves travel through the cribriform foramina to reach the anterior cranial fossa, where they communicate with the olfactory bulb in order to detect odours.
The optic canal permits the passage of the optic nerve (CN II) and the ophthalmic artery into the bony orbit. Specifically, it is bounded medially by the body of the sphenoid, and laterally by the lesser wing of the sphenoid bone. The optic nerve carries light-sensitive rods and cones from the retina to the brainstem, allowing us to form a visual image.
The superior orbital fissure is a cleft that opens anteriorly into the orbit, and enables communication between the cavernous sinus and the apex of the orbit. It is bordered superiorly by the lesser wing and inferiorly by the greater wing of the sphenoid bone. The superior orbital fissure transmits the following structures:
The foramen rotundum is located at the base of the greater wing of the sphenoid, inferior to the superior orbital fissure. It provides a connective passage between the middle cranial fossa and the pterygopalatine fossa, allowing the maxillary nerve (branch of the trigeminal nerve, CN V) to pass through.
The foramen ovale is another opening located at the base of the greater wing of the sphenoid. It is positioned posterolateral to the foramen rotundum within the middle cranial fossa. It permits the passage of the mandibular nerve (branch of the trigeminal nerve, CN V) and the accessory meningeal artery. The mandibular nerve carries the feeling of touch, temperature, and pain to the face.
The internal acoustic meatus is a bony passage located within the petrous part of the temporal bone. It is an opening that connects the posterior cranial fossa with the inner ear, transporting the facial and vestibulocochlear nerves (CN VII and VIII) alongside the vestibular ganglion and labyrinthine artery. The facial nerve is responsible for facial expression, while the vestibulocochlear nerve is responsible for hearing and balance.
The jugular foramen is formed anteriorly by the petrous part of the temporal bone and posteriorly by the occipital bone. It can be considered as three separate compartments with their respective contents: the anterior compartment contains the inferior petrosal sinus (a dural venous sinus); the middle compartment transmits the glossopharyngeal nerve, vagus nerve and cranial part of the accessory nerve.
The anatomical foramina and keystone structures of the skull provide the necessary pathways for the passage of axons, arteries, and nerves. These pathways connect the anterior cranial fossa with the nasal cavity, the middle cranial fossa with the orbit, and the posterior cranial fossa with the inner ear.
The superior orbital fissure is located within the middle cranial fossa of the sphenoid bone. It is bordered superiorly by the lesser wing and inferiorly by the greater wing of the sphenoid bone. The superior orbital fissure allows for the passage of a number of key structures. These include the lacrimal nerve (branch of the ophthalmic nerve, the first division of the trigeminal nerve), the frontal nerve (branch of the ophthalmic nerve, the first division of the trigeminal nerve), the superior ophthalmic vein, the trochlear nerve (CN IV), the superior division of the oculomotor nerve (CN III), the nasociliary nerve (branch of the ophthalmic nerve, CN V1), and the inferior division of the oculomotor nerve (CN III).
The foramen rotundum is located in the middle cranial fossa of the sphenoid bone. It is positioned at the base of the greater wing of the sphenoid bone, inferior to the superior orbital fissure. The foramen rotundum allows the passage of the maxillary branch of the trigeminal nerve (CN V).
The foramen ovale is located in the middle cranial fossa of the sphenoid bone, posterolateral to the foramen rotundum. It allows the passage of the mandibular branch of the trigeminal nerve (CN V) as well as the accessory meningeal artery.
The foramen spinosum is located within the middle cranial fossa, laterally to the foramen ovale. It permits the passage of the middle meningeal artery, the middle meningeal vein, and the meningeal branch of CN V3.
The internal acoustic meatus is situated in the petrous part of the temporal bone, in the middle cranial fossa. Through it pass the facial nerve (CN VII), the vestibulocochlear nerve (CN VIII), the vestibular ganglion, and the labyrinthine artery.
The jugular foramen is located within the posterior cranial fossa of the occipital bone. This foramen transmits the glossopharyngeal nerve (CN IX), the vagus nerve (CN X), the accessory nerve (CN XI), and the jugular bulb, as well as their associated vessels (the inferior petrosal and sigmoid sinuses).
The hypoglossal canal is situated within the occipital bone, through which the hypoglossal nerve (CN XII) passes to exit the posterior cranial fossa.
The olfactory foramen is composed of two foramina: the optic canal and the superior orbital fissure. They connect the anterior cranial fossa with the nasal cavity. These foramina permit the passage of the axons of the olfactory nerve from the olfactory epithelium in the nose into the anterior cranial fossa, where they communicate with the olfactory bulb. The optic canal allows for the passage of the optic nerve (CN II) and the ophthalmic artery into the bony orbit. It is bordered medially by the body of the sphenoid, and laterally by the lesser wing of the sphenoid bone.
The superior orbital fissure is a cleft that opens into the orbit anteriorly and enables communication between the cavernous sinus and the apex of the orbit. It transmits numerous structures, listed below in order from superior to inferior: the lacrimal nerve (branch of the ophthalmic nerve, the first division of the trigeminal nerve), the frontal nerve (branch of the ophthalmic nerve, the first division of the trigeminal nerve), the superior ophthalmic vein, the trochlear nerve (CN IV), the superior division of the oculomotor nerve (CN III), the nasociliary nerve (branch of the ophthalmic nerve, the first division of the trigeminal nerve), the inferior division of the oculomotor nerve (CN III), the abducens nerve (CN VI), and a branch of the inferior ophthalmic vein.
The anatomical foramina and structures of the skull provide essential pathways for the passage of axons, arteries, and nerves. Understanding the key structures and their locations is critical to comprehending the anatomy of the cranial cavity and its vital functions.
The Cranial Foramina are openings in the skull that serve as passages for the cranial nerves, arteries, veins, and the spinal cord. With the proper knowledge of cranial anatomy, the importance of the different foramina can be understood.
The Anterior Cranial Fossa, located within the Ethmoid Bone, contains the Cribriform Plate, through which the Olfactory Nerve (CN I) passes. The Middle Cranial Fossa, located within the Sphenoid Bone, has several foramina each serving different structures. The Optic Canal passes the Optic Nerve (CN II), Ophthalmic Artery, Lacrimal Nerve, Frontal Nerve, Superior Ophthalmic Vein, Trochlear Nerve, and Superior Division of the Oculomotor Nerve (CN III), Nasociliary Nerve, and Inferior Division of the Oculomotor Nerve (CN III). The Foramen Rotundum allows passage for the Maxillary Branch of the Trigeminal Nerve (CN V), Mandibular Branch of the Trigeminal Nerve (CN V), Middle Meningeal Artery, Middle Meningeal Vein, and Meningeal Branch of CN V3. The smaller Foramen Ovale passes the Facial Nerve (CN VII), Vestibulocochlear Nerve (CN VIII), Vestibular Ganglion, and Labyrinthine Artery. The Foramen Spinosum allows passage of the Middle Meningeal Artery, Middle Meningeal Vein, and Meningeal Branch of CN V3. The Internal Acoustic Meatus passes the Facial Nerve (CN VII), Vestibulocochlear Nerve (CN VIII), Vestibular Ganglion, and Labyrinthine Artery. The posterior cranial fossa is located in both Occipital and Temporal Bones.
The Jugular Foramen, located in the Posterior Cranial Fossa of both the Petrous Part of the Temporal Bone and Occipital Bone, passes the Glossopharyngeal Nerve (CN IX), Vagus Nerve (CN X), Accessory Nerve (CN XI), Inferior Petrosal Sinus, Sigmoid Sinus, and Jugular Bulb. The Hypoglossal Canal, located in the Posterior Cranial Fossa of the Occipital Bone, is a passage for the Hypoglossal Nerve (CN XII). Lastly, the largest foramen, the Foramen Magnum, located in the Posterior Cranial Fossa of the Occipital Bone, serves as a passage for the Vertebral Arteries, Medulla and Meninges, CN XI (spinal division), Dural Veins, Anterior and Posterior Spinal Arteries.
Understanding the different foramina is key in the anatomic knowledge of the head and neck. It is important to note that each of the foramina serve a different purpose and passage for many structures. For example, the Anterior Cranial Fossa is where the Olfactory Nerves (CN I) pass through. In the Middle Cranial Fossa, the Optic Canal passes the Optic Nerve (CN II), Ophthalmic Artery, Lacrimal Nerve, Frontal Nerve, Superior Ophthalmic Vein, Trochlear Nerve, and Superior Division of the Oculomotor Nerve (CN III). The Foramen Rotundum allows for the passage of the Maxillary Branch of the Trigeminal Nerve (CN V), Mandibular Branch of the Trigeminal Nerve (CN V), Middle Meningeal Artery, Middle Meningeal Vein, and Meningeal Branch of CN V3.
The Posterior Cranial Fossa serves as a passage for many structures. The Jugular Foramen passes the Glossopharyngeal Nerve (CN IX), Vagus Nerve (CN X), Accessory Nerve (CN XI), Jugular Bulb, Inferior Petrosal Sinus, and Sigmoid Sinus. The Hypoglossal Canal is a passage for the Hypoglossal Nerve (CN XII). Lastly, the Foramen Magnum passes the Vertebral Arteries, Medulla and Meninges, CN XI (spinal division), Dural Veins, and Anterior and Posterior Spinal Arteries.
In life, the Foramen Lacerum, located at the junction of the Sphenoid, Temporal and Occipital Bones, is filled by cartilage and only a few minor vessels pass through it. Knowing the specific structures that pass through the different foramina is important for any medical practitioner as they can appropriately diagnose any issue related to the aforementioned structures, treat the area accordingly, and provide further advice to the patient.
The cranial foramina are essential structures in the anatomy of the head and neck. Collectively, they provide a passage for all the necessary structures, such as cranial nerves, arteries, veins, and the spinal cord. Knowing the anatomical information of the different foramina is paramount in understanding the anatomy of the head and neck, and is beneficial in any medical field where the head or neck region is involved.
