The Infratemporal Fossa
The infratemporal fossa is a complex and irregularly shaped space, located deep to the masseter muscle. It acts as a conduit for many neurovascular structures that travel between the cranial cavity and other structures of the head.
In this article we shall look at the anatomy of the infratemporal fossa – its boundaries, contents, and clinical significance.
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 connected to the pterygopalatine fossa by the pterygomaxillary fissure and also communicates with the temporal fossa superiorly.
The boundaries of the infratemporal fossa are formed by bone and soft tissue:
- Lateral – ramus of the mandible.
- Medial – lateral pterygoid plate of the sphenoid.
- Anterior – posterior surface of the maxilla.
- Posterior – carotid sheath.
The floor of the infratemporal fossa is comprised of the medial pterygoid muscle, while the roof is formed by the greater wing of the sphenoid bone. Two foramina open out on the roof – the foramen ovale and foramen spinosum. They provide a connection with the cranial cavity.
Clinical Relevance – Surface Anatomy of the Infratemporal Fossa
Ok, so the first and most useful thing is to figure out where the infratemporal fossa is. The easiest method is this – clench your jaw, and feel for the ridge of the masseter muscle in your cheek. You’re basically 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. At this point, you need to start using your imagination a bit.
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 between the cranial cavity, pterygopalatine fossa and temporal fossa. It also contains some of the muscles of mastication.
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.
There are numerous nervous structures located within the infratemporal fossa:
- 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 (terminal branch of the external carotid artery) travels through the infratemporal fossa. Within the fossa, it gives rise to the middle meningeal artery, which travels into the cranial cavity via the foramen spinosum. Clinically this is important as a site of traumatic bleed as the middle meningeal passes underneath the pterion.
The pterygoid venous plexus is directly connected to the cavernous sinus, and drains the eye and its locality. Infections of the skin and eye socket are able to track back into the plexus, and on up into the cavernous sinus where meningitis is a substantial risk. Other veins in the fossa include the maxillary vein and middle meningeal vein, both of which you might expect.
Clinical Relevance: Fractures of the Pterion
Where the temporal, parietal, frontal and sphenoid bones meet, the skull is at its weakest, and susceptible to fracture. This point is known as the pterion.
The middle meningeal artery (MMA) supplies the skull and the dura mater (the outer membranous layer covering the brain). It travels underneath the pterion, thus a fracture of the skull at the pterion can injure or completely lacerate the MMA.
Blood will then collect in between the dura mater and the skull, causing a dangerous increase in intra-cranial pressure. This is known as an extradural haematoma.
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 hemorrhages.