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Foramina of the Skull Clinical Relevance There are foramina in the skull through which multiple vital neurological and vascular structures pass. Knowledge of the 'normal' route structures take through the foramen is relevant as it provides the ability to differentiate structures on imaging from potential pathology (e.g. tumours, bleed). Furthermore, combining the clinical presentation and the arrangement of structures within a foramen can be crucial in identifying the underlying cause and location of pathology. Below are some examples of the route that structures take through the foramen and some of the clinical manifestations of pathology due to the underlying anatomy. INJURIES Severe head injuries involving the anterior cranial fossa can result in the olfactory bulb being torn from the olfactory nerves. Head injuries can often present with few symptoms and can be difficult to identify without imaging. A patient presenting with torn olfactory nerves (CN I) would have lost the ability to smell (anosmia), providing a clue that the injury was located in the anterior cranial fossa. INTERNAL ACOUSTIC MEATUS Cranial nerves VII (facial) and VIII (vestibulocochlear) and their branches pass through the internal acoustic meatus in order to exit the cranial cavity. The nerves (and branches) positions are most constant in the lateral portion of the meatus which is divided into superior and inferior portions by a horizontal ridge (Figure 1). Foramina of the Skull Figure 1. Schematic diagram depicting a right internal acoustic meatus and in which order structures pass through the foramen. Superior: Facial and superior vestibular nerve (facial nerve is situated anteriorly) Facial nerve is separated laterally to the superior vestibular nerve by a vertical ridge of bone from the temporal bone (Bill's bar) Inferior: Cochlear and inferior vestibular nerve (cochlear nerve is situated anteriorly) Clinical relevance: A common type of brain tumour, an acoustic neuroma, most often arises in the posterior aspect of the internal acoustic meatus. Due to the underlying anatomy: Vestibular nerves are most likely to be damaged (compressed), resulting in problems with balance Facial nerve innervation (to the muscles of expression and parotid gland (etc...)) will be preserved Cochlear nerve innervation will be preserved (no loss of hearing) Foramina of the Skull If undetected an acoustic neuroma will continue to grow and will eventually cause damage to the facial and cochlear nerves. INTERNAL CAROTID ARTERY The internal carotid artery enters the middle cranial fossa of the cranial cavity by the carotid canal found in the temporal bone anterior to the jugular foramen. Shown in Figure 2, the canal ascends vertically and then bends to open superior to the foramen lacerum (which is filled with cartilage). The internal artery then enters the cavernous sinus (a large venous plexus) and continues to travel anteriorly along the skull surface towards the optic canal (Figure 3). Within the cavernous sinus the abducent (CN VI) nerve is also found. Clinical relevance: Cavernous sinus thrombosis or internal carotid artery can compress and damage the abducent nerve (CN VI) Loss of innervation to the superior oblique muscle of the eye The affected eye rotates medially causing blurred vision - a subtle clinical sign for a potentially life threatening issue Foramina of the Skull Figure 2. The path of the internal carotid artery into the cranial cavity and the relevant anatomical relations. Figure 3. Coronal view of the internal carotid artery within the cavernous sinus. Foramina of the Skull