Anatomy clinical correlates: Temporal regions, oral cavity and nose

The face is made up of a large network of nerves, vessels, muscles, and other structures which are susceptible to disease. In particular, there are many clinical conditions that affect the temporal region, oral cavity, and nose. Understanding the anatomy of these areas can help us better understand the clinical presentation, complications and management of these conditions. So let’s get face to face with our… well, face!

First up, the parotid gland. Remember that the facial nerve enters the parotid gland to form the parotid plexus and give rise to the temporal, zygomatic, buccal, marginal mandibular, and cervical branches. However, these branches don't actually innervate the gland but just pass through it to exit at its borders. The auriculotemporal nerve, which is a branch of the mandibular nerve, courses superficially to the gland and is responsible for general sensation of the gland. Additionally, parasympathetic innervation from the glossopharyngeal nerve travels with the auriculotemporal nerve to innervate the parotid gland.

Now, understanding these anatomical relationships is also important when it comes to surgery to the parotid gland, as the majority of salivary gland tumors occur within the parotid gland which are often surgically removed. During parotid gland surgery, the surgeon needs to identify, dissect, and isolate the facial nerve and its branches with great care, so that there’s no damage to them. See, if the nerve or one of its branches is damaged, that causes paralysis of some or all facial muscles on that side. The auriculotemporal nerve also requires special care to avoid damaging it during surgery, because during healing the nerve can go on to reinnervate into the sweat glands of the overlying skin. So instead of salivating when eating or thinking about food, this reinnervation causes excessive sweating and redness of the cheek during the normal parasympathetic response. This condition is called Frey syndrome.

Now let’s move a bit up and talk about the temporomandibular joint, starting with dislocations. The temporomandibular joint can be dislocated in multiple directions, with the most common being anterior dislocation. This is when the condyle of the mandible is displaced anteriorly from its articulation within the mandibular fossa of the squamous portion of the temporal bone. It most commonly occurs when there is extreme jaw opening causing excessive translational movement, and can occur when yawning, having a seizure or dental procedure, or undergoing intubation. A traumatic force to the jaw, especially when the mouth is open, can result in dislocation to the side of the blow. Posterior dislocations, on the other hand, are very rare because the postglenoid tubercle, with help from the strong intrinsic lateral ligament which holds the joint together, limit posterior movement.

Any dislocation of the TMJ can also be accompanied by fractures of the mandible, and it can result in stretching of the surrounding ligaments causing pain; as well as spasm of the mastication muscles, particularly the lateral pterygoids, which can actually prevent the joint from popping back into place on its own. In this case, a manual reduction is required. If surgery is needed, damage to the overlying facial nerve and auriculotemporal nerve and its TMJ articular branches may occur. Damage to the articular branches of the TMJ can lead to joint laxity and instability. Common clinical features of temporomandibular joint dislocation include the inability to close the mouth, difficulty speaking, drooling, and pain in front of the ear.

On the other hand, temporomandibular joint disorder is an umbrella term that refers to many conditions affecting the joint itself and the muscles of mastication, where the etiology is multifactorial. Typical symptoms include jaw tenderness, jaw pain that worsens with opening the mouth, difficulty opening and closing the mouth with clicking, headaches, and neck stiffness. Repetitive jaw motions such as gum chewing, as well as clenching and grinding of the jaw is considered a leading cause of the temporomandibular joint disorder. Other causes involve trauma and jaw misalignment. TMJ disorder may be associated with hypersensitivity of the mandibular nerve, which can cause pathologic contraction of the pterygoids and masseter muscles exacerbating pain and jaw dysfunction. Furthermore, in addition to supplying the TMJ the mandibular nerve also provides cutaneous innervation to the ear and external auditory canal. Therefore, TMJ disorders can result in otalgia due to referred pain to the ear.

Time for a quick break. What structures can be damaged during parotid gland surgery? What is the most common type of TMJ joint dislocation?

Great! Now let’s switch gears and look at the oral cavity. Surgery of the oral cavity is not uncommon. Whether it is a third molar extraction, dental implant surgery, or tumor removal, care must be taken to preserve the inferior alveolar nerve.

As a little reminder, this nerve passes through the mandibular canal and provides innervation to the mandibular molar and premolar teeth, and the surrounding gingiva. It continues as the mental nerve, which innervates the anterior teeth and the surrounding gingiva, the skin of the chin, and the lower lip. Because of its close relation to the teeth, the inferior alveolar nerve is the most commonly injured nerve during oral surgery. Symptoms usually include paresthesia, complete numbness, or pain in the teeth, gingiva, chin, and lower lip.

However, numbness in this area isn’t always a bad thing. For example, an inferior alveolar nerve block is a common anesthetic method to reduce pain during dental procedures, where a local anesthetic agent is injected near the mandibular foramen to numb the inferior alveolar nerve. Specifically, the needle is inserted between the two important landmarks: the coronoid notch, and the pterygomandibular raphe. This way the mandibular teeth, gingiva, lower lip, and chin are anesthetized. Part of the tongue can be anesthetized as well, because the anesthetic may also bath the lingual nerve.

Another commonly used nerve block is the greater palatine nerve block. In this case, the anesthetic is inserted at the greater palatine foramen. This way all of the palatal mucosa and lingual gingiva posterior to the maxillary canines and underlying bone of the palate of one side are anesthetized.

The third type of block is the nasopalatine nerve block. The anesthesia is inserted into the nasopalatine foramen. This block anesthetizes the palatal mucosa, gingiva, and the six anterior maxillary teeth.