The infratemporal fossa is an irregular space inferior to the temporal fossa and deep to the ramus of the mandible. It is densely packed with muscles and neuro-vasculature, in close communication with the temporal fossa and pterygopalatine fossa. While tumors originating in this region are rare and often benign, they frequently invade neighboring structures. The infratemporal fossa’s deep anatomical relationships and proximity to various cranial nerves make it a challenging space for surgical resection. In the present study, a model which accurately depicts the complex anatomy of this area as a tool to augment surgical education is described. CT angiography data from a healthy 29-year-old female was segmented and refined based on a compilation of data from published anatomical studies. The resulting anatomical details were subsequently incorporated into a 3D model by a professional medical illustrator using Maxon ZBrush. Meshes were further refined in digital 3D space based on data from peer-reviewed anatomical studies. The final 3D model demonstrates the complex anatomical structures within the infratemporal fossa, including their relationship with important cranial base and neurovascular structures relevant to surgical approaches in this area.
Introduction
The infratemporal fossa (ITF) is a dense irregular anatomic space, located inferior to the temporal bone and greater wing of the sphenoid bone and medial to the ramus of the mandible. The nomenclature derives from its location: inferior ( Infra- ) to the temporal fossa (-Temporal ). This space contains a number of important anatomic structures including the internal maxillary artery (IMAX), the mandibular branch of the trigeminal nerve (CNV3), the pterygoid muscles, and the pterygoid venous plexus. The ITF is clinically and surgically important as it communicates with other anatomic spaces, including the pterygopalatine fossa (PPF), which can harbor a diverse array of infectious and neoplastic pathologies. While tumors in this region can originate from the ITF itself, they often invade into the ITF from neighboring areas. Due to its deep anatomic location, and proximity to important vessels and cranial nerves, tumors of the ITF pose a surgical challenge, especially with pathologic involvement of the skull base. The anatomy in this area is complex, and accurate anatomic modeling is required to facilitate safe surgical approaches.
Currently, anatomy of the ITF is commonly taught in 2-dimensions (2D), which provides a limited conceptual model of the complex relationships between structures that occupy this space. Both open and endoscopic surgical approaches necessitate a 3-dimensional (3D) understanding of anatomy which is incompletely captured by 2D illustrations. Outside of the surgical field, cadaveric dissections provide valuable 3D modeling, especially with complex anatomic areas such as the ITF, but may not be widely available, and are difficult to review after the cadaveric dissection based on captured images and the need to remove superficial structures to expose deeper anatomy. By creating an anatomically accurate model of the ITF, we seek to provide an effective, accessible tool for teaching and learning anatomy in this area.
Methods
A detailed review of the methodology used to create this model has been described by Silver, et al. In brief, the medial and lateral pterygoids, tensor veli palatini (TVP), and levator veli palatini (LVP) muscles were all segmented from the CT angiogram of a healthy 29-year-old female. Imaging artifacts were removed, and structures were imported into a 3D illustration program. The structures were further refined by descriptions from the literature of the most common anatomic variants. Where multiple variants were described, study size, quality and anatomical detail were used to determine the most common representative structure. The model was then refined by an experienced medical illustrator to render a final production, which was uploaded to an online viewer (Medreality, Thyng LLC, Illinois, USA).
Results
The ITF is an irregular space located medial to the ramus of the mandible. While the exact anatomic boundaries are a subject of debate, for the purposes of the present model, we will consider them as following: anteriorly bordered by the posterolateral surface of the maxillary sinus; posteriorly, by the tympanic part of the temporal bone, including the styloid process; superiorly, by the squamous part of the temporal bone and the inferior aspect of the greater wing of the sphenoid bone; laterally, by the medial aspect of the zygomatic arch and the mandibular ramus; and medially, by the lateral pterygoid plate anteromedially and the TVP and medial pterygoid muscle postero-medially. The ITF communicates with the temporal fossa laterally via the space medial to the zygomatic arch, the PPF medially, via the pterygomaxillary fissure, and the orbit antero-superiorly via the inferior orbital fissure. Its boundaries are outlined in Figure 1 .
Musculature relationships
Lateral pterygoid
The lateral pterygoid muscle largely occupies the superior portion of the ITF, connecting the greater wing of the sphenoid and the pterygoid plates to the mandibular condyle. Merlino et al. previously provided a detailed 3D description of this muscle. The function of the lateral pterygoid is to primarily depress and protrude the mandible, facilitating chewing, jaw opening and speech. The mandibular and buccal nerves, branches of CNV3, innervate the lateral pterygoid. Blood supply comes from IMAX and facial artery. The lateral pterygoid has 2 heads; the superior head, which originates at the inferior surface of the temporal bone and greater wing of the sphenoid, and the inferior head, which originates at the inferior two-thirds of the lateral surface of the lateral pterygoid plate, both of which insert at the condylar process of the mandible.
Medial pterygoid
Located inferior to the ITF, the medial pterygoid muscle contains 2 heads. The anterior belly arises from the pyramidal process of the palatine bone and the maxillary tuberosity of the maxilla. The posterior belly originates from the medial surface of the lateral pterygoid plate and pterygoid fossa. The anterior and posterior belly insert on the anterior angle of the mandible just posterior to the mylohyoid and the angle of the mandible, respectively. As described by Merlino et al. the medial pterygoid fascia serves to separate the ITF from the parapharyngeal space.
Tensor veli palatini and levator veli palatini
The TVP and LVP are muscles originating in the masticator space and both course through the ITF. The LVP originates from skull base, at the bony-cartilaginous transition point of the eustachian tube (ET) within the ITF, and then travels inferomedially along the border of the ET to the soft palate. It raises the palate to close the nasopharynx from the oropharynx. Similarly, the TVP arises at the skull base near the ET and inserts on at the soft palate as a component of the palatine aponeurosis, serving to tighten this aponeurosis and open the eustachian tube.
Sphenomandibular ligament
The sphenomandibular ligament serves to prevent inferior distraction of the mandible and regulate movement of the articular disc and malleolus. , This structure is variably described, but is most commonly thought to originate at the spine of the sphenoid posteriorly and travel to the posterior border, and medial aspect of the lingula of the mandible. , Notably, its exact attachments are often debated, with studies that suggest there is no direct attachment to the sphenoidal spine, but instead to the area of the petrotympanic fissure, and others that describe fibers that extend from the sphenoid spine to petrotympanic fissure posteriorly and directly attach to the temporomandibular articular disc. Along with the sphenoid spine, the sphenomandibular ligament serves as a landmark for procedures within the ITF. , The ligament’s course creates a pocket between it and the condylar process of the mandible, by which the auriculotemporal nerve (ATN), inferior alveolar nerve (IAN), IMAX, and its inferior alveolar branch pass through. , , The sphenomandibular ligament is generally described as spreading along the medial aspect of the inferior alveolar vascular bundle, placing this neurovasculature in close proximity to the mandible .
Vascular relationships
Pterygoid venous plexus
The pterygoid venous plexus occupies a large portion of the ITF, serving as an anastomotic network of veins, that drain into the maxillary vein, passing between the sphenomandibular ligament and the mandibular neck. The plexus arises from venules attached to the 4 masticatory muscles, with various venous bridges connecting to muscular venous sheets. The pterygoid plexus, as seen in Figure 2 , serves as a primary drainage site for the nasal cavity, paranasal sinuses and nasopharynx. The plexus is subdivided into 2 areas: a superficial component, located between the temporalis and lateral pterygoid muscles, and a deep component between the medial and lateral pterygoid muscles. In 1996, Deplus et al. described the plexus as spanning both aspects of the lateral pterygoid muscle. In this study, symmetry was noted in 9/10 subjects between the right and left plexuses, however asymmetry in venous size was commonly noted. A second anatomical study by Bernal–Manas described the plexus as located posteromedial to the condylar joint complex while intertwining with the lateral pterygoid muscle anteromedially. In relation to the temporomandibular joint, it was found that while the pterygoid venous plexus surrounds the whole joint, including capsular and lateral pterygoid muscular insertions, it is primarily located on the medial aspect of the articular complex. The maxillary vein serves as the primary drainage pathway for the pterygoid plexus, joining the superficial temporal vein to form the external jugular vein. ,
Maxillary artery
Upon branching from the external carotid artery, the IMAX courses medially, through the ITF and into the PPF. This artery is classically subdivided into 3 distinct segments: mandibular, pterygoid, and pterygopalatine. The mandibular segment, which is primarily located within the masticator space, arises within the parotid gland as the terminal branch of the external carotid artery (ECA), traveling posteriorly towards the lateral pterygoid. Within the ITF, the maxillary artery lies lateral and superficial to the buccal, lingual, and inferior alveolar nerves and superficial to the lateral pterygoid muscle. , The artery transverses the space between the mandible and the sphenomandibular ligament, running adjacent to the auriculotemporal nerve. , The first branch of the pterygoid segment is the middle meningeal artery (MMA). The MMA runs superficial to the lateral pterygoid muscle and can originate as a common trunk with the inferior alveolar artery. , The MMA ascends to pass through the foramen spinosum to enter the intracranial cavity, exiting the ITF on its superior boundary. The pterygoid segment of the maxillary artery also gives rise to the accessory meningeal artery, exiting via the foramen ovale, and the mandibular artery, which enters the mandibular foramen in the medial surface of the mandible to supply the mandible and inferior teeth. Both the anterior and posterior deep temporal arteries arise from the IMAX, traveling along the infratemporal crest alongside the deep temporal branches of the mandibular nerve and innervating the temporalis muscle. The IMAX ultimately courses between the 2 heads of the lateral pterygoid to enter the PPF via the pterygomaxillary fissure, at which point it transitions into the pterygopalatine segment. The PPF is described within this issue in Calcano, et al.
Neural relationships
Mandibular segment of the trigeminal nerve (CNV3)
The mandibular segment of the trigeminal nerve arises at the trigeminal ganglion in the middle cranial fossa, providing both sensory fibers to the mandibular teeth, gingiva of mandible, anterior 2/3 of the tongue, oral cavity mucosa, lower lip, skin over the lower face, and motor fibers to muscles of mastication, as well as the tensor tympani and TVP. , Entering through the foramen ovale on the lateral aspect of the parapharyngeal space, CNV3 courses laterally and superiorly to the otic ganglion, dividing into anterior and posterior trunks. , The anterior trunk splits immediately after its exit from the skull base and gives rise to primarily muscular fibers via the deep temporal, mesenteric, and lateral pterygoid nerves. The posterior trunk, which is much larger in size, gives off sensory afferents via the buccal, lingual, inferior alveolar nerve (IAN) and auriculotemporal nerve (ATN). Figure 3 shows the relationship between the IMAX, IAN and ATN. For anatomic proximity, the mandibular branch, IAN and lingual nerve are consistently found within 8 mm of the foramen ovale.
The buccal nerve
The buccal nerve arises from the anterior trunk of CNV3, beneath the anterior border of the masseter muscle at the level of the occlusal plane, carrying sensory fibers that supply the lower buccal gingiva, lower buccal sulcus, and cheek mucosa. The buccal nerve can be traced on or within a fine fascial sheath covering the deep aspect of the temporal muscle where it then emerges from the 2 heads of the lateral pterygoid muscle. , Occasionally, the deep temporal nerve can be seen arising as a branch of the buccal nerve. The buccal nerve then descends anterolaterally, traveling below the inferior portion of the temporalis muscle, deep to the mandible and masseter muscle, coursing between the coronoid process and tuberosity of the maxilla, and emerging out from under the mandibular ramus and masseter muscle. , , The buccal nerve continues anteriorly where it anastomoses with buccal branches of the facial nerve. ,
The masseteric nerve
The masseteric nerve also branches off the anterior trunk of CNV3. The masseter nerve begins at the angle between the temporomandibular joint and zygomatic arch. It passes laterally above the lateral pterygoid muscle, anterior to the TMJ and posterior to the tendon of the temporalis. The masseteric nerve crosses the posterior part of the mandibular coronoid notch and enters the deep surface of the masseter, giving off a branch prior to entering the muscle which supplies the TMJ. As it exits the mandibular notch, it is accompanied by the masseteric artery. In a study of 33 hemi heads, it was found to have 2 branches at the level of the mandibular notch in 47.2% of specimens and 1 branch in 25% of specimens. The frequent branching patterns of the masseteric nerve makes it a primary donor for facial reanimation surgery as severe disfunction or atrophy to the masseter muscle is not commonly anticipated.
The deep temporal nerve
Arising from the anterior trunk of the CNV3, the deep temporal nerve courses superior to the lateral pterygoid muscle, entering deep into the temporalis muscle. Variable branching patterns have been described, with origins from the anterior trunk itself, or from more distal branches of both the anterior and posterior trunks, such as the buccal and masseteric nerves.
The auriculotemporal nerve
The ATN is a direct branch of the posterior trunk of CNV3, arising after CNV3 descends medial to the lateral pterygoid. In Iwanaga et al.’s anatomical study of the ATN, they found that 11/14 ATNs arose from a single main trunk of CNV3, while in 3/14 cases there were 2 main trunks (duplicated) that had branched prior to leaving the retromandibular space. The ATN courses superficial to the superficial temporal artery then posteriorly between the sphenomandibular ligament and the neck of the mandible, running laterally behind the TMJ to emerge deep in the upper part of the parotid gland. This nerve maintains communication with the facial nerve at the neck of the condyle. The ATN is closely associated with the middle meningeal artery within the ITF. Branches of the ATN go on to innervate the TMJ, parotid gland, external acoustic meatus, anterior auricle, zygoma, and superficial temporal region.
The inferior alveolar nerve (IAN)
The IAN arises from CNV3 just distal to the foramen ovale, paralleling the trajectory of the ATN, between the sphenomandibular ligament and mandibular ramus, prior to entering the mandibular canal via the mandibular foramen. , Once in the mandibular canal, it courses anteroinferiorly towards the apices of the teeth, dividing into the mental branches which terminate at the first and second premolars. , With relation to the inferior alveolar vasculature, a cadaveric study using 56 hemi-heads, demonstrated the IAN courses anterior or anteromedially to the inferior alveolar artery in 79% of specimens, with a similar relationship to the inferior alveolar vein in 71% of specimens.
The lingual nerve
The lingual nerve begins its course just inferior to the foramen ovale where it branches from CNV3 via a common trunk with the IAN. The lingual nerve courses towards the medial pterygoid muscle, with a path that is medial and anterior to the IAN, , running between the TVP and the lateral pterygoid muscles. The chorda tympani branch of the facial nerve joins the lingual nerve just distal to its course between the TVP and lateral pterygoid muscles. As the lingual nerve courses anteriorly along the surface of the medial pterygoid muscle, it gradually moves closer to the medial surface of the mandibular ramus until it reaches the junction of the vertical and horizontal rami of the mandible. At this juncture it continues its course towards the posterior root of the third molar tooth where it supplies sensory fibers to the mucosa, the floor of the mouth, the lingual gingiva and the mucosa of the anterior two-thirds of the tongue. , ,
The chorda tympani nerve
The chorda tympani nerve branches from the facial nerve within the facial canal, just proximal to its exit at the stylomastoid foramen. , The nerve carries taste fibers (visceral afferent) to the anterior two-thirds of the tongue and parasympathetic fibers (visceral efferent) to the submandibular and sublingual salivary glands. , Following its course through the middle ear, the chorda tympani nerve enters the ITF via the petrotympanic fissure, descending in an anterior and inferior direction toward the ATN and IAN. Within the ITF, the chorda tympani nerve takes a curved course from the skull base, running medially to the TMJ, reaching approximately the same horizontal plane as the lower part of the mandibular notch where it then anastomosis with the lingual nerve.
The otic ganglion
Just below the foramen ovale and medial to CNV3, the otic ganglion lies deep to the lateral pterygoid muscle within the ITF. , , Grossly described as small, oval, and having a flattened shape, the ganglion receives multiple contributions, with motor, sensory, parasympathetic, and sympathetic roots. While a comprehensive description of otic ganglion function is outside the scope of this article, it has been well described by previous authors. Though topographically, it is related to CNV3, the otic ganglion also maintains functional relations with both the glossopharyngeal and facial nerves. The ganglion has several branches, but most studies describe parasympathetic and sympathetic branches, with common reports of additional muscular branches. , The ganglion shares numerous connections with the branches of CNV3 via the ATN, lingual nerve, IAN, buccal nerve and meningeal nerve, as it provides postganglionic parasympathetic fibers to these branches. Additional communications with the facial nerve motor fibers of the LVP muscle are commonly described. , , In most anatomic studies, the otic ganglion can be identified bilaterally, though with significant variability in anatomic structure. ,
Bony landmarks
The infratemporal fossa is primarily defined by its osseous boundaries, with limited bony structure within the ITF itself. For bony landmarks, the zygomatic root provides a reliable basis to approximate distance to the foramen ovale and spinosum, with an average distance of 2.6 and 3.2 cm, respectively, between these structures and the zygomatic root. The lateral pterygoid plate serves as an important landmark as it can be traced posteriorly to the anterior aspect of foramen ovale. Bony landmarks are important when percutaneously accessing the foramen ovale for treatment of trigeminal neuralgia as it helps guide the introducer cannula, avoiding damage to critical neurovascular structures.
Discussion
The ITF is a unique anatomic area within the head and neck, encompassing several critical neurovascular structures such as the pterygoid segment of the maxillary artery with associated branches, several divisions of CNV3, the pterygoid venous plexus, and the pterygoid musculature. Due to several osseous corridors, the ITF is intimately associated with adjacent anatomic areas such as the PPF, temporal fossa, and masticator space.
Infratemporal pathology: anatomic considerations
Infratemporal pathology primarily arises from either neoplastic or infectious processes, with tumors being the most common, an estimated 80% of which are benign. Given the open connections to the adjacent anatomic areas, a majority (70%-75%) of tumors involving the ITF spread from contiguous anatomic areas such as the PPF or nasopharynx medially, the middle cranial fossa superiorly, the EAC laterally, or the parapharyngeal space and parotid gland inferiorly. , Primary tumors are rarer (25%-30%), with meningiomas or peripheral nerve sheath tumors like schwannomas being the most common, classically spreading the medial and lateral pterygoids as they arise from the IAN or lingual nerves. Due to the numerous branches of the trigeminal nerve as it exits the skull base, it is important to interrogate nerves such as the auricular temporal nerve for perineural tumor spread. This is especially important in patients with facial nerve symptoms and masticator space masses due to the connections between CN V and CN VII through this region. Communication between these nerves can facilitate perineural tumor spread involving the auriculotemporal nerve which is often overlooked at the level above the ECA bifurcation. Auricular temporal nerve perineural tumor spread should be suspected when CNV3, either alone or in combination with facial nerve main trunk is involved. Auricular temporal nerve perineural tumor spread can be seen in Figure 4 . In contrast, hemangiomas arising from the pterygoid venous plexus are generally located between the lateral pterygoid muscle and the temporalis muscle. Infections within the ITF also occur via contiguous spread from odontogenic or sinonasal sources. Generally, odontogenic causes arise in the setting of poor dental health and in proximity to dental procedures, where infection travels superiorly along the mandibular ramus to seed the ITF. ITF infections often present with nonspecific symptoms of pain, swelling, and trismus, while classic signs and symptoms such as cranial neuropathies involving CNV3 hypoesthesia and facial nerve paresis are present in a minority (<25%) of cases.
