The external nose is a visible facial structure projecting above the nasal cavity. This article will discuss the anatomical features of the external nose, including its skeletal structure, muscles, blood supply, and innervation.
The external nose is said to have a pyramidal shape, with a nasal root located superiorly and continuous with the forehead. An apex of the nose terminates inferiorly in a rounded ‘tip’, and the dorsum of the nose spans between the root and apex. Just inferior of the apex are the nares, which are piriform openings into the vestibule of the nasal cavity. The nares are bounded medially by the nasal septum and laterally by the ala nasi (the lateral cartilaginous wings of the nose).
The skeletal structure of the external nose consists of both bony and cartilaginous components. This includes the nasal bones, maxillae and frontal bone at the superior portion and two lateral cartilages, two alar cartilages and one septal cartilage at the inferior portion, as well as some smaller alar cartilages. The skin overlying the bony part of the nose is thin, whereas the skin over the cartilaginous part is thicker and contains many sebaceous glands, extending into the vestibule of the nose via the nares.
The saddle nose deformity is a result of nasal trauma, where septal support to the nose is lost and the middle part of the nose appears sunken. This is due to either direct damage to the septal bone or cartilage, or a consequence of nasal septal haematoma.
The external nose contains a number of small muscles that insert into it, contributing to facial expression. These muscles are innervated by branches of the facial nerve (CN VII). The procerus muscle originates in the fascia overlying the nasal bone and lateral nasal cartilage, inserting into the inferior forehead. It contributes to depressing the medial eyebrows and wrinkling the skin of the superior dorsum, aided by the transverse portion of the nasalis muscle. The alar part of nasalis arises from the maxilla and inserts into the major alar cartilage, allowing the muscle to dilate the nares. This action is assisted by the depressor septi nasi.
The skin of the external nose receives arterial supply from branches of the maxillary and ophthalmic arteries, with additional supply from the angular artery and lateral nasal artery (both branches of the facial artery, derived from the external carotid artery). It is drained of venous blood through the facial vein, and ultimately into the internal jugular vein, along with superficial lymphatic vessels accompanying it. These lymphatic vessels ultimately drain into the deep cervical lymph nodes.
The unique venous drainage of the nose and surrounding area is due to the communication between the facial vein and cavernous sinus via the ophthalmic vein, otherwise known as the 'Danger Triangle of the Face.'
The external nose is an important feature of the face, and has a pyramidal shape, created by the external nares, nasal septum and alar cartilages. In terms of structure, the external nose comprises the septal cartilage, paired upper lateral cartilages, paired lower lateral cartilages, and alar cartilages. Here, there are hairs that function to filter air as it enters the respiratory system.
A number of small muscles insert into the external nose, contributing to facial expression. All these muscles are innervated by branches of the facial nerve (CN VII). The procerus muscle originates in the fascia overlying the nasal bone and lateral nasal cartilage, and inserts into the inferior forehead. Contraction of this muscle can depress the medial eyebrows, and wrinkles the skin of the superior dorsum. The transverse portion of the nasalis muscle assists the procerus muscle in this action, while the alar part of nasalis arises from the maxilla, inserting into the major alar cartilage and allowing the muscle to dilate the nares, “flaring” them. This action is assisted by the depressor septi nasi.
The external nose receives arterial supply from branches of the maxillary and ophthalmic arteries. The septum and alar cartilages receive additional supply from the angular artery and lateral nasal artery. These are both branches of the facial artery (derived from the external carotid artery). Venous drainage is into the facial vein, and then in turn into the internal jugular vein. Lymphatic drainage from the external nose is via superficial lymphatic vessels accompanying the facial vein.
Sensory innervation of the external nose is derived from the trigeminal nerve (CN V). The external nasal nerve, a branch of the ophthalmic nerve (CN V1), supplies the skin of the dorsum of the nose, nasal alae and nasal vestibule, while the lateral aspects of the nose are supplied by the infrorbital nerve, a branch of the maxillary nerve (CN V2). Motor innervation to the nasal muscles of facial expression is via the facial nerve (CN VII).
The venous drainage of the nose and surrounding area is unique as a result of communication between the facial vein and cavernous sinus, via the ophthalmic vein. As the cavernous sinus lies within the cranial cavity, this enables infections from the nasal area to spread to the brain. This retrograde spread of infection can cause cavernous sinus thrombosis, meningitis or brain abscess, and such conditions are indicative of dysfunction in the area known as the Danger Triangle of the Face.
The Danger Triangle of the Face is an anatomical region that is bounded by the two angles of the mouth and the bridge of the nose. It is of particular importance due to the proximity of the facial vessels and nerves, which connect with the cavernous sinus. As such, any infections or abscesses that are present on the face may be spread via these facial vessels and nerves into the cavernous sinus and then via venous channels to the brain. The facial nerve itself is particularly vulnerable to infections as it is a voluminous nerve running superficial to the temporal bone.
Therefore, conditions such as rhinitis or sinusitis may spread retrogradely, and may present with neurological symptoms such as headache, fever and paralysis. The Danger Triangle of the Face should always be considered when assessing disease or infection in the face, and such conditions should be investigated and treated promptly.
