Infratemporal Fossa - Clinical Tree

Atlas References

Netter: 9, 10, 55–62, 64, 81–84
McMinn: 42, 44, 76
Gray's Atlas: 507, 527–533

Before You Begin

The infratemporal fossa dissection requires the use of an electric saw or a hammer and chisel. Make sure that you wear eye protection when you use these tools.
Cut the terminal branches of the facial nerve, and reflect the nerves posteriorly toward the parotid gland ( Fig. 22.1 ).
Similarly, cut the parotid duct as it penetrates the buccinator muscle ( Fig. 22.2 ), and reflect it posteriorly toward the parotid gland (see Fig. 22.1 ).
Palpate the zygomatic arch, and expose it from the surrounding adipose tissue and temporal fascia ( Fig. 22.3 ).

Dissection Steps

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Identify the temporalis muscle, and trace its course medial to the zygomatic arch ( Fig. 22.4 ).
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Clean the lateral surface of the masseter muscle, and expose its borders ( Fig. 22.5 ).
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Detach the masseter muscle from the inferior border of the zygomatic arch ( Fig. 22.6 ), and reflect it inferiorly toward the angle of the mandible.
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Clean the remaining soft tissues over the mandible, and expose its surface ( Fig. 22.7 ).
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Identify the temporal, zygomatic, and mandibular bony regions.
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Just deep to the anterior border of the ramus of the mandible, in the fat and connective tissue of the anterior edge of the temporalis muscle, identify and clean the buccal nerve, a branch of the mandibular division (V3) of the trigeminal nerve.
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Place scissors or a probe underneath the zygomatic arch.
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Using a saw, cut the zygomatic arch just anterior to the attachment of the masseter muscle ( Fig. 22.8 ).
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Make a second cut through the arch just posterior to the masseter and anterior to the temporomandibular joint ( Fig. 22.9 ).
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Detach the cut piece of zygomatic bone ( Fig. 22.10 ).
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With scissors, cut the temporalis muscle from the coronoid process and ramus of the mandible ( Fig. 22.11 ).
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Reflect the temporalis upward, and clean the soft tissues and fat over the mandibular notch ( Fig. 22.12 ).
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Place your scissors or a probe or scalpel handle immediately beneath the ramus of the mandible ( Fig. 22.13 ).
o
Push the soft tissues, musculature, and vessels inferiorly.

Dissection Tip

This maneuver (see Fig. 22.13 ) is important for preserving underlying structures when the mandible is cut. You may leave the probe or scissors in place to protect the inferior alveolar neurovascular bundle and lingual nerve when you perform the cut (see next step).

o
With an electric saw, cut horizontally through the ramus of the mandible 2 to 3 inches (5–7.5 cm) below the coronoid process, leaving the articular process in place ( Fig. 22.14 ).
o
Reflect the severed coronoid process and the temporalis muscle superiorly ( Figs. 22.15 to 22.17 ).

Dissection Tip

Take special care when you reflect the coronoid process and the temporalis muscle so as not to injure the buccal nerve.

o
As the temporalis is reflected superiorly, observe the deep temporal arteries supplying this muscle.

Dissection Tip

You can choose either to sever the arteries or to keep them. In this dissection, we choose to keep the deep temporal vessels (see Figs. 22.16 and 22.17 ).

o
Once temporalis has been reflected, identify the medial pterygoid muscle (see Figs. 22.15 to 22.17 ).
o
Once the temporalis muscle is reflected and the soft tissues are cleaned, identify and expose the lateral pterygoid muscle, which lies just beneath the temporalis ( Fig. 22.18 ).

Anatomy Note

The lateral pterygoid muscle arises from the lateral pterygoid plate and passes horizontally to insert onto the articular disc of the temporomandibular joint (see Fig. 22.18 ).

Anatomy Note

In some cadavers, a variant muscle may be seen in the infratemporal fossa. In this specimen, a pterygoideus proprius was identified (muscle of Henle). This muscle originates from the anterior infratemporal crest, runs vertically downward to insert onto the lateral pterygoid plate, and crosses superficially to the lateral pterygoid muscle (see Fig. 22.18 ). Typically, the muscle of Henle has no functional significance, but it may compress the mandibular nerve, resulting in possible trigeminal neuralgia.

o
Clean the soft tissues and fat at the inferior border of the lateral pterygoid muscle ( Fig. 22.19 and Plate 22.1 ).
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Identify the inferior alveolar nerve and inferior alveolar artery superficial to the medial pterygoid muscle (see Figs. 22.18 and 22.19 ).
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Clean the inferior alveolar nerve and trace it to the mandibular foramen.
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Look at the lateral surface of the inferior alveolar nerve, and note the small branch that runs parallel with it, the nerve to the mylohyoid muscle (see Fig. 22.19 ).

Anatomy Note

The nerve to the mylohyoid arises just before the inferior alveolar nerve enters the mandibular foramen. The nerve to the mylohyoid travels inferiorly, beneath the ramus and body of the mandible, to innervate the mylohyoid muscle and the anterior belly of the digastric muscle.

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Lateral to the inferior alveolar nerve, identify the lingual nerve ( Figs. 22.20 and 22.21 ).
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Medial to the inferior alveolar nerve, identify the buccal nerve.
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Immediately underneath these nerves, observe the medial pterygoid muscle passing from the pterygoid plate to its insertion onto the inferior and posterior parts of the medial surface of the mandibular ramus.
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Identify and expose the maxillary artery (see Fig. 22.19 to 22.21 and see Fig. 22.29 ).

Anatomy Note

In the majority of cadavers, the lateral pterygoid muscle is crossed superficially by branches of the maxillary artery; in the remaining specimens, the artery travels deep to the muscle (see Fig. 22.21 ).

o
Proceed by carefully detaching the lateral pterygoid muscle from its origin on the pterygoid plate with scissors and forceps ( Figs. 22.22 to 22.24 ).

Dissection Tip

Removing the lateral pterygoid muscle can be a challenge. Be patient, and detach its muscle fibers carefully, paying special attention to the branches of the maxillary artery underneath it (see Figs. 22.22 through 22.24 ).

o
Carefully remove all soft tissues around the maxillary artery.
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Posterior to the inferior alveolar artery and nerve and anterior to the medial pterygoid muscle, identify the sphenomandibular ligament.

Dissection Tip

This ligament is thin and may resemble a nerve, and it is often confused with the inferior alveolar nerve.

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Once the lateral pterygoid muscle is removed, expose the maxillary artery and its branches ( Fig. 22.25 ).
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Note the retromandibular vein formed by the junction of the superficial temporal and maxillary veins (see Fig. 22.25 ).
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Identify the middle meningeal artery, which typically runs vertically toward the sphenoid bone, to enter the foramen spinosum (see Figs. 22.25 and 22.27 ).
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Identify the two roots of the auriculotemporal nerve, which, in the majority of cases, you will find encircling the middle meningeal artery ( Figs. 22.26 and 22.27 and Plates 22.2 and 22.3 ).
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Lift the lingual nerve, and trace it superiorly until you see it joined on its posterior surface by a small nerve, the chorda tympani, which is a branch of the facial nerve ( Fig. 22.28 ). If this nerve is not evident, clean the soft tissue around the lingual nerve more posteriorly.
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Clean the lingual and inferior alveolar nerves, and trace their passage deep to the medial pterygoid muscle.
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Deep to the infratemporal fossa, trace and follow the termination of the maxillary artery, the sphenopalatine artery, toward the sphenopalatine foramen ( Figs. 22.29 and 22.30 ).
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Typically, two additional branches are easily identifiable. Identify the infraorbital artery as it ascends to enter the infraorbital canal, and the posterior superior alveolar artery as it descends to enter the infratemporal surface of the maxilla (see Fig. 22.30 ).
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Identify the mandibular canal and the inferior alveolar nerve ( Figs. 22.31 to 22.33 ).
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With an electric drill, cut the mandible in a direction demarcating a line between the mandibular canal and mental foramen (see Fig. 22.32 ).
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With fine forceps, lift the small branches of the inferior alveolar nerve terminating on the teeth ( Fig. 22.34 ).
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Using a bone saw, make a shallow parasagittal cut through the temporomandibular joint. Identify the articular disc, the two synovial cavities, and the articular capsule of that joint.