In this chapter, we review the anatomy of the extracranial lateral skull base and the course of the facial nerve. It is important that the surgeon knows this anatomy before approaching lesions of the infratemporal fossa.
10.1 Anatomy and Exploration of the Infratemporal Fossa
Step 6. Exposure of middle meningeal artery (Fig. 10.20)
Step 7. Dissection of pterygoid muscles (Fig. 10.21)
Step 8. Identification of styloid muscles (Fig. 10.28)
Illustrated Steps with Commentary
Fig. 10.1 Anatomy of the infratemporal skull base.The skin is raised and the subcutaneous layers are demonstrated. The superficial temporal artery runs lateral to the temporoparietal muscle. (FM, frontal muscle; fSTA, frontal branch of the superficial temporal artery; GAN, great auricular nerve; Pl, platysma; pSTA, parietal branch of the superficial temporal artery; SCM, sterno-cleidomastoid muscle; TPM, temporoparietal muscle; ZMjM, zygomaticus major muscle)Fig. 10.2 Superficial temporal artery.The superficial temporal artery runs lateral to the temporoparietal muscle that continues into the galea aponeurotica. The anterior part of the galea aponeurotica, the frontal muscle, is seen at the forehead. The auriculotemporal nerve, a branch of the trigeminal nerve, is also seen. The nerve runs parallel to the superficial temporal artery around the root of the zygoma. (ATN, auriculo-temporal nerve; FM, frontal muscle; fSTA, frontal branch of the superficial temporal artery; G, galea aponeurotica; pSTA, parietal branch of the superficial temporal artery; TPM, temporoparietal muscle)Fig. 10.3 (Step 1) Exposure of the facial nerve and the superficial layer of the parotid gland.After removing the temporoparietal muscle and the fascia of the masseteric muscle, the branches of the facial nerve, the masseteric muscle, and the superficial lobe of the parotid gland are seen. (BB, buccal branch of the facial nerve; GAN, great auricular nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; SCM, sternocleidomastoid muscle; sPG, superficial layer of the parotid gland; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)Fig. 10.4 Deep lobe of the parotid gland.After removing the superficial lobe of the parotid gland, the deep layer of the parotid gland is seen. The facial nerve runs between the superficial and deep layer of the parotid gland. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; dPG, deep layer of the parotid gland; GAN, great auricular nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; SCM, sternocleidomastoid muscle; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)Fig. 10.5 Five branches of the facial nerve.Once the superficial lobe of the parotid gland is removed, the major branches of the facial nerve are exposed. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; OA, ophthalmic artery; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve; XI, accessory nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)Fig. 10.6 (Step 2) The digastric branch of the facial nerve.The first branch of the facial nerve, the digastric branch, originates from the proximal portion of the extracranial facial nerve, just distal to the stylomastoid foramen. It can be found by rotating the superior margin of the digastric muscle. This is an easy way to locate the facial nerve at the time of surgery. (DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MsT, mastoid tip; OA, ophthalmic artery; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen)Fig. 10.7 The digastric branch of the facial nerve.The relationship between the digastric branch of the facial nerve and the posterior belly of the digastric muscle is more fully demonstrated after the occipital artery is divided. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve)Fig. 10.8 Exposure of the distal external carotid artery.The neck of the mandible and the external carotid artery are seen after the deep layer of the parotid gland is removed. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)Fig. 10.9 Anterior dissection exposing the zygomaticus major muscle.The zygomaticus major muscle originates from the lateral surface of the zygomatic bone and inserts into the angle of the mouth. The zygomaticus minor muscle lies just medial to the zygomaticus major muscle. The zygomaticofacial nerve, a branch of the maxillary nerve (the second division of the trigeminal nerve) is also seen exiting from the zygomaticofacial foramen. This nerve, along with the zygomaticotemporal nerve, can be injured during a zygomatic osteotomy. (DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; LOR, lateral orbital rim; MM, masseteric muscle; RM, ramus of the mandible; ZFF, zygomaticofacial foramen; ZMjM, zygomaticus major muscle; Zy, zygoma)Fig. 10.10 (Step 3) Exposing the masseteric muscle.The masseteric nerve is seen just posterior to the masseteric muscle. The nerve that passes through the mandibular notch is a branch of the mandibular nerve (the third division of the trigeminal nerve). (DB, digastric branch; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IJV, internal jugular vein; MM, masseteric muscle; MN, masseteric nerve; RM, ramus of the mandible; SCM, sternocleidomastoid muscle; XI, accessory nerve; Zy, zygoma)Fig. 10.11 Layers of the masseteric muscle.The masseteric muscle consists of three layers: the superficial, the middle, and the deep layers. The superficial layer (peeled off in this photo) is the largest and arises from a thick aponeurosis originating from the maxillary process of the zygomatic bone and from the anterior two-thirds of the inferior border of the zygomatic arch. The middle layer arises from the medial aspect of the anterior two thirds of the zygomatic arch and from the lower border of the posterior third of this arch. The deep layer arises from the medial surface of the zygomatic arch. The muscle inserts into the lateral ramus and coronoid process of the mandible. (DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IJV, internal jugular vein; mMM, middle layer of the masseteric muscle; RM, ramus of the mandible; sMM, superficial layer of the masseteric muscle; XI, accessory nerve; Zy, zygoma)Fig. 10.12 Insertion of the temporalis muscle.The coronoid process of the mandible where the temporalis muscle inserts is exposed after the masseteric muscle has been removed. (BM, buccal muscle; CnP, condylar process; CrP, coronoid process; DM, digastric muscle; DTA, deep temporal artery; ECA, external carotid artery; FN, facial nerve; MN, masseteric nerve; RM, ramus of the mandible)Fig. 10.13 Exposure of the deep temporal nerve and the masseteric nerve.With the masseteric muscle removed, the posterior deep temporal nerve to the temporalis muscle and the nerve to the masseter muscle are clearly seen along with the deep temporal artery. Cauterizing the undersurface of the temporalis muscle risks injury to the deep temporal nerves and deep temporal artery. (CnP, condylar process; CrP, coronoid process; DTA, deep temporal artery; DTN, deep temporal nerve; FN, facial nerve; MN, masseteric nerve; RM, ramus of the mandible; TM, temporalis muscle)Fig. 10.14 (Step 4) Pterygoid venous plexus.The rich pterygoid venous plexus surrounds the lateral pterygoid muscles. This plexus communicates with numerous skull base, orbital, and dural veins, including the cavernous sinus. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; CrP, coronoid process; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; LOR, lateral orbital rim; MN, masseteric nerve; PVP, pterygoid venous plexus; RM, ramus of the mandible; SCM, sternocleidomastoid muscle)Fig. 10.15 Magnified view of Fig. 10.14.This figure demonstrates some of the branches of the internal maxillary artery, deep temporal artery, and nerve. (CnP, condylar process; CrP, coronoid process; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; LOR, lateral orbital rim; LPM, lateral pterygoid muscle; MA, maxillary artery; MN, masseteric nerve; PVP, pterygoid venous plexus; RM, ramus of the mandible)Fig. 10.16 (Step 5) Removal of the central portion of the ramus of the mandible.Anatomical structures behind the mandible are exposed. The inferior alveolar artery is seen branching from the maxillary artery, and accompanied by the inferior alveolar nerve. The lingual nerve runs parallel to the inferior alveolar nerve, passing from the medial surface of the lateral pterygoid muscle to the lateral surface of the medial pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; CrP, coronoid process; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; LN, lingual nerve; LPM, lateral pterygoid muscle; MA, maxillary artery; MN, masseteric nerve; PVP, pterygoid venous plexus; SCM, sternocleidomastoid muscle)Fig. 10.17 The buccal nerve and the maxillary artery.After the pterygoid venous plexus is removed, the superior and inferior heads of the lateral pterygoid muscle are well seen. The buccal nerve lies in between these two heads to provide sensation to the cheek. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle)Fig. 10.18 Exposure of the maxillary artery, the inferior alveolar nerve, and the lingual nerve.The buccal nerve passes between the two heads of the lateral pterygoid muscle and the lingual nerve passes beneath the inferior head of the lateral pterygoid muscle. The mylohyoid nerve branches from the inferior alveolar nerve. (BM, buccal muscle; BN, buccal nerve; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle)Fig. 10.19 The sphenomandibular ligament.The sphenomandibular ligament descends from the sphenoidal spine to the lingular of the mandible. It is separated from the mandible by the maxillary artery and the inferior alveolar artery and nerve. (BN, buccal nerve; DB, digastric branch; DM, digastric muscle; ECA, external carotid artery; FA, facial artery; FN, facial nerve; IJV, internal jugular vein; MA, maxillary artery; MT, maxillary tuberosity; SHM, stylohyoid muscle; SML, sphenomandibular ligament)Fig. 10.20 (Step 6) The middle meningeal artery.The middle meningeal artery emerges from the maxillary artery and passes deep to the lateral pterygoid muscles to enter the foramen spinosum. (BN, buccal nerve; DB, digastric branch; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MMA, middle meningeal artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)Fig. 10.21 (Step 7) The lateral and medial pterygoid muscles.The two distinct heads of the lateral pterygoid muscle originate from the greater wing of the sphenoid bone and the lateral surface of the lateral pterygoid plate and insert into the neck of the condyle of the mandible. The larger deep head of the medial pterygoid muscle arises from the medial surface of the lateral pterygoid process and inserts into the medial surface of the ramus of the mandible. The smaller superficial head arises from the tuberosity of the maxilla. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MHN, mylohyoid nerve; MMA, middle meningeal artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)Fig. 10.22 Relationship between the lateral and medial pterygoid muscles.The medial pterygoid muscle is seen inferior to the lateral pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; sLPM, superior head of the lateral pterygoid muscle)Fig. 10.23 The deep and superficial heads of the medial pterygoid muscle.The superficial head of the medial pterygoid muscle has been raised. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)Fig. 10.24 The lateral pterygoid muscle.The buccal nerve emerges between the superior and inferior heads of the lateral pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)Fig. 10.25 The lateral lamina of the pterygoid process.The inferior head of the lateral pterygoid muscle arises from lateral surface of the lateral pterygoid process. That muscle has been removed to reveal the lateral pterygoid process. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)Fig. 10.26 The lingual and inferior alveolar nerve.The relationship between the lingual nerve and the inferior alveolar nerve is demonstrated. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MMA, middle meningeal artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; STA, superior temporal artery)Fig. 10.27 The chorda tympani.The inferior alveolar nerve has been detached and elevated. The chorda tympani, a branch of the facial nerve, joins the lingual nerve coursing to the tongue. The chorda tympani exits the skull on the medial surface of the spine of the sphenoid bone. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MMA, middle meningeal artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SHM, stylohyoid muscle; STA, superior temporal artery)Fig. 10.28 (Step 8) The styloid muscles.The neck and condyle of the mandible and the external carotid artery have been removed. Three muscles, the stylohyoid, the styloglossus, and the stylopharyngeal muscles that attach to the styloid process are seen. The internal carotid artery runs medial to these muscles. (BM, buccal muscle; DM, digastric muscle; FA, facial artery; FO, foramen ovale; IJV, internal jugular vein; LPP, lateral lamina of the pterygoid process; MT, maxillary tuberosity; OA, ophthalmic artery; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process; TVPM, tensor velli palatini muscle)Fig. 10.29 The styloid muscles.The styloid muscles and stylohyoid ligament are exposed in another specimen. The mandible and external carotid artery have been removed. (C6, C6 portion of the internal cerebral artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; SCM, sternocleidomastoid muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process)Fig. 10.30 The foramen ovale from the lateral side.The pterygoid muscles, the mandible, and the external carotid artery have been removed. This view gives the surgeon a sense of the relationship between the foramen ovale and the lateral pterygoid plate. This relationship is important to keep in mind when drilling through the middle fossa. The pterygoid plates will be encountered when drilling anterior to the line connecting the foramen ovale and foramen rotundum. We clearly see the middle meningeal artery entering the foramen spinosum and the distal branches of the internal maxillary artery in the pterygopalatine fossa. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DB, digastric branch; DM, digastric muscle; FA, facial artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; IJV, internal jugular vein; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MMA, middle meningeal artery; MT, maxillary tuberosity; OA, ophthalmic artery; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process)Fig. 10.31 Anatomical structures in the parapharyngeal space.Medial to the pterygoid muscles, we see the pharyngeal muscles. Demonstrated are the superior constrictor muscle, tensor velli palatini muscle, buccinator muscle, and maxillary tuberosity. The maxillary tuberosity and the adjacent palatine bone give rise to the superficial head of the medial pterygoid muscle. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; FO, foramen ovale; ICA, internal carotid artery; IJV, internal jugular vein; LPP, lateral lamina of the pterygoid process; MMA, middle meningeal artery; MT, maxillary tuberosity; OA, ophthalmic artery; SConsM, superior constrictor muscle; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process; TVPM, tensor velli palatini muscle)
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