The Infratemporal Fossa
The infratemporal fossa is a complex area located at the base of the skull, deep to the masseter muscle.
It is closely associated with both the temporal and pterygopalatine fossae and acts as a conduit for neurovascular structures entering and leaving the cranial cavity.
This article will outline the borders and content of the fossa before examining its clinical relevance.
The infratemporal fossa can be said to have a wedge shape. It is located deep to the masseter muscle and zygomatic arch (to which the masseter attaches). The fossa is closely associated with both the pterygopalatine fossa, via the pterygomaxillary fissure, and also communicates with the temporal fossa, which lies superiorly (figure 1.0).
The boundaries of this complex structure consists of both bone and muscle:
- Lateral – condylar process and ramus of the mandible bone
- Medial – lateral pterygoid plate; tensor veli palatine, levator veli palatine and superior constrictor muscles
- Anterior – posterior border of the maxillary sinus
- Posterior – carotid sheath
- Roof – greater wing of the sphenoid bone
- Floor – Medial pterygoid muscle
The roof of the infratemporal fossa, formed by the greater wing of the sphenoid bone, provides an important passage for the neurovascular structures transmitted through the foramen ovale and spinosum. Among these are the mandibular branch of the trigeminal nerve and the middle meningeal artery.
Clinical Relevance: Surface Anatomy of the Infratemporal Fossa
You can find your own infratemporal fossa by clenching your jaw and feeling for the ridge of the masseter muscle in your cheek. This is right above the fossa. Trace posteriorly over the muscle until you reach the anterior edge of the jaw, and you’re in line with the posterior of the fossa. Now relax your jaw, and trace your fingers forwards across your cheek, along the lower edge of the zygomatic process of your temporal bone, followed by the zygomatic bone, and finally to the zygomatic process of the mandible. This is anterior border.
The lateral border of the fossa is actually quite deep – the ramus of the mandible – meaning we’re on the inside face of the jawbone. To get to the medial border, we go even deeper, to the lateral edge of the sphenoid bone, in an area called the lateral pterygoid plate. You can think of this as being roughly in line with the molars of your upper jaw. The sphenoid bone also contributes to the superior border, this time it’s the greater wing.
The inferior border is the medial pterygoid muscle, which stretches to the posterior inferior border of the ramus of the mandible.
The infratemporal fossa acts as a pathway for neurovascular structures passing to and from the cranial cavity, pterygopalatine fossa and temporal fossa. It also contains some of the muscles of mastication. In fact, the lateral pterygoid splits the fossa contents in half – the branches of the mandibular nerve lay deep to the muscle, while the maxillary artery is superficial to it.
The infratemporal fossa is associated with the muscles of mastication. The medial and lateral pterygoids are located within the fossa itself, whilst the masseter and temporalis muscles insert and originate into the borders of the fossa.
The infratemporal fossa forms an important passage for a number of nerves originating in the cranial cavity (figure 1.2):
- Mandibular nerve – a branch of the trigeminal nerve (CN V). It enters the fossa via the foramen ovale, giving rise to motor and sensory branches. The sensory branches continue inferiorly to provide innervation to some of the cutaneous structures of the face.
- Auriculotemporal, buccal, lingual and inferior alveolar nerves – sensory branches of the trigeminal nerve.
- Chorda tympani – a branch of the facial nerve (CN VII). It follows the anatomical course of the lingual nerve and provides taste innervation to the anterior 2/3 of the tongue.
- Otic ganglion – a parasympathetic collection of neurone cell bodies. Nerve fibres leaving this ganglion ‘hitchhike’ along the auriculotemporal nerve to reach the parotid gland.
The maxillary artery, the terminal branch of the external carotid artery, travels through the infratemporal fossa. Within the fossa, it gives rise to the middle meningeal artery, which passes through the superior border via the foramen spinosum.
The pterygoid venous plexus is directly connected to the cavernous sinus and drains the eye. Infections of the skin and eye socket are able to track back into this plexus within the fossa and up into the cavernous sinus, making meningitis is a substantial risk. Other veins in the fossa include the maxillary vein and middle meningeal vein.
Clinical Relevance – Fractures of the Pterion
The pterion is an important structure in cranial anatomy. It is the point where the temporal, parietal, frontal and sphenoid bones meet and the skull is at its weakest. Trauma in this region can lead to an extradural haematoma as the middle meningeal artery (MMA) lies deep to it.
An extradural haematoma causes a dangerous increase in intra-cranial pressure, which can lead to herniation of brain tissue and ischaemia.
The increase in intra-cranial pressure causes a variety of symptoms; nausea, vomiting, seizures, bradycardia and limb weakness. It is treated by diuretics in minor cases, and drilling burr holes into the skull in the more extreme haemorrhages.