ENT Anatomy

ENT Anatomy

Sarah K. Rapoport


Understanding the structural details of the ear, nose, and throat is imperative for accurate diagnosis of its pathologies. Formulating a conceptual map of these regions can prove invaluable for diagnosing and treating disorders of the ears, nose, and throat, as well as avoiding some of their lurking pitfalls.

The Scalp

The five tissue layers that comprise the scalp (skin, connective tissue composed of superficial fascia, galea aponeurosis, loose areolar tissue, and periosteum or pericranium) form a dense, protective covering for the skull (Figure 1.1A). The scalp is thickest in its hair-bearing regions and grows thinner in areas without hair follicles.1 The frontalis muscle lies beneath the anterior skin and subcutaneous tissue layers of the scalp. This muscle is a continuation of the galea aponeurosis layer anteriorly and helps to protect the pericranium.

Laterally, the galea aponeurosis extends to form the temporoparietal fascia and the superficial musculoaponeurotic system (SMAS). The galea aponeurosis is most dense and adherent to the underlying scalp at the vertex. It gradually becomes looser the more laterally it extends, especially in areas of muscle and fascial attachment. The pliability of this tissue is relevant when you need to repair simple and complex lacerations of the scalp.

The scalp has a luxuriant vasculature system, so even small lacerations can generate copious bleeds. The internal carotid arteries provide tributaries for the arterial vasculature of the forehead and scalp. As demonstrated in Figure 1.1B, the supratrochlear artery is a branch of the ophthalmic artery and runs along the anterior forehead. After branching from the ophthalmic artery, the supratrochlear artery emerges from the orbital septum above the trochlear notch, where it travels between the corrugator and frontalis muscles to pass vertically along the forehead to the scalp. Together with its corresponding nerve, a branch of the ophthalmic distribution of the trigeminal nerve (CN V1), the supratrochlear artery is reliably located 1.7 to 2.2 cm from the midline of the forehead (which usually aligns with the medial border of the eyebrow).2 The supraorbital artery, also a branch of the ophthalmic artery, runs just lateral and parallel to the supratrochlear artery along the anterior forehead. The supraorbital artery passes through the supraorbital notch, penetrates the corrugator muscle, and then divides into superficial and deep branches that ascend laterally to anastomose with the superficial and deep temporal arteries that supply blood to the remainder of the scalp.

The Paranasal Sinuses

The paranasal sinuses lie deep to the face, scalp, and forehead. Once developed, these paired and aerated cavities occupy the bony spaces around the eyes and nose. The paranasal sinuses serve
multiple purposes, including decreasing the weight of the skull, acting as pathways to filter inhaled pathogens or allergens, providing drainage outflow tracts for mucus accumulation, and absorbing forceful blunt trauma to the face. These sinuses include the frontal, ethmoid, maxillary, and sphenoid paranasal sinuses, depicted in Figure 1.2, and reliably distribute the impact of blunt facial trauma to protect critical structures such as the eyes and brain.3 These sinuses are lined with respiratory mucosa composed of pseudostratified ciliated columnar epithelium. And firmly adherent to the periosteum or perichondrium of the adjacent bone and cartilage of the sinuses lies a rich capillary network.

The Facial Nerve

The facial nerve is a mixed (motor, special sensory, and autonomic) nerve that originates in the brainstem, courses through the temporal bone of the skull, and exits the skull base through the stylomastoid foramen. As a mixed nerve, it has multiple roles: (1) its motor nucleus innervates the muscles of facial expression, digastric, stylohyoid, and stapedius muscles, (2) its superior salivatory nucleus provides preganglionic parasympathetic innervation to the lacrimal and salivary glands, and (3) its solitary tract nucleus receives sensory innervation, sound, and taste (special sensory), respectively, from the posterior superior external auditory ear canal (EAC) and from the anterior two-thirds of the tongue.4 Violation of the facial nerve along its course can compromise these functions and produce facial paralysis, loss of taste, and hyperacusis. For example, tumors can infiltrate or compress the nerve, infections such as otitis externa or herpes zoster can inflame or compress the nerve, and trauma can directly sever or stretch the nerve.

To reach the mimetic (facial) muscles, the facial nerve travels through the parotid gland, dividing it into its deep and superficial lobes. After exiting the parotid gland, the facial nerve branches into its five principal motor branches: temporal, zygomatic, buccal, marginal mandibular, and cervical (Figure 1.3). The facial nerve is located deep to the facial muscles, with three exceptions: the buccinator, mentalis, and levator anguli oris muscles. These three muscles are located underneath the facial nerve and are innervated along their superficial surfaces.

Confirming intact function of the facial nerve in patients presenting with symptoms of the ear, nose, and throat is a mandatory component of a thorough exam. In cases of facial nerve dysfunction or injury, it is critical to determine whether there is adequate eye closure, because it is important to protect the cornea of a patient with facial palsy. The facial nerve innervates the orbicularis oculi muscles, sphincteric muscles that surround the eye. To test orbicularis oculi function, ask the patient to squeeze their eyelids shut tightly, and test the patient’s resistance to your elevating the eyelid. If you simply ask a patient to close their eyes, gravity can help lower the eyelid, and the oculomotor nerve will elevate the eyelid via the levator palpebrae superioris, giving the false impression that the patient’s eye closure and elevation are adequate when they may actually be impaired.

The Ear

The external ear, also referred to as the pinna or the auricle, helps funnel sound into the ear canal, where it can be directed to the tympanic membrane (TM) and ossicles to reach the inner ear (cochlea) and auditory nerve. The external components of the ear are illustrated in Figure 1.4A and include the helix, antihelix, tragus, antitragus, conchal bowl, and lobule. The superficial temporal and posterior auricular arteries provide the blood supply to the external ear, which is composed of skin, subcutaneous tissue, muscles, and perichondrium that supplies blood to the underlying elastic cartilage. Trauma that damages or elevates the perichondrium off the cartilage risks devascularizing the cartilage, because the cartilage does not contain its own blood vessels and relies on its overlying perichondrium for diffusion of nutrients.5

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Apr 18, 2023 | Posted by in OTOLARYNGOLOGY | Comments Off on ENT Anatomy

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