Cleft Palate

Anatomy of the Palate

The palate (also known as the ‘roof of the mouth’) forms a division between the nasal and oral cavities. It is separated into two distinct parts – a hard palate comprised of bone and an immobile structure and a soft palate comprised of muscle fibres covered by a mucous membrane. The soft palate can be elevated to close the pharyngeal isthmus during swallowing, aiding to prevent food entry into the nasopharynx.

Structure

The palate divides the nasal cavity and the oral cavity, with the hard palate positioned anteriorly and the soft palate posteriorly. It forms both the roof of the mouth and the floor of the nasal cavity, resulting in different mucosal linings on the superior and inferior palatal surfaces. The superior aspect of the palate is lined with respiratory epithelium, whilst the inferior aspect is lined with oral mucosa, populated by secretory salivary glands.

Hard Palate

The hard palate forms the anterior aspect of the palate. It is composed of the palatine processes of the maxilla and the horizontal plates of the palatine bones. Three main foramina/canals are present in the hard palate – an incisive canal located in the anterior midline for the transmission of the nasopalatine nerve, a greater palatine foramen located medial to the third molar tooth for the transmission of the greater palatine nerve and vessels, and lesser palatine foramina located in the pyramidal process of the palatine bone for the transmission of the lesser palatine nerve.

Soft Palate

The soft palate is located posteriorly and is mobile. It is comprised of muscle fibres covered by a mucous membrane and is continuous with the hard palate anteriorly and with the palatine aponeurosis. The posterior border of the soft palate is free - i.e. not connected to any structure - and has a central process that hangs from the midline, known as the uvula. The soft palate also forms the roof of the fauces - an area connecting the oral cavity and the pharynx - with two arches binding the palate to the tongue and pharynx; the palatoglossal arches anteriorly and the palatopharyngeal arches posteriorly. The palatine tonsils are found between these two arches and reside in the tonsillar fossae of the oropharynx.

Muscles of the Soft Palate

There are five muscles which give the actions of the soft palate. They are all innervated by the pharyngeal branch of the vagus nerve (CN X) – apart from the Tensor veli palatini which is innervated by the medial pterygoid nerve (a branch of CN V3).

• Tensor veli palatini – originates from the medial pterygoid plate of the sphenoid and inserts into the palatine aponeurosis. It functions to tense the soft palate.
• Levator veli palatini – arises from the petrous temporal bone and the eustachian tube, before inserting into the palatine aponeurosis. It functions to elevate the soft palate.
• Palatoglossus – originates from the palatine aponeurosis, and travels anteriorly, laterally and inferiorly to insert into the side of the tongue. It functions to pull the soft palate towards the tongue.
• Palatopharyngeus – arises from the palatine aponeurosis and the hard palate, and inserts into the upper border of the thyroid cartilage. It functions to tense the soft palate and draw the pharynx anteriorly on swallowing.
• Musculus uvulae – arises from the posterior nasal spine and the palatine aponeurosis, and inserts into the mucous membrane of the uvula. It functions to shorten the uvula.

The palate is a complex structure which has both form and function; it divides the nasal and oral cavities, and its composition of muscles allows it to be mobile, being able to elevate the soft palate to aid swallowing.

Greater and Lesser Palatine Foramina

The greater palatine foramen is located medial to the third molar tooth, and it transmits the greater palatine nerve and vessels. Meanwhile, the lesser palatine foramina are located in the pyramidal process of the palatine bone and transmit the lesser palatine nerve.

The Soft Palate

Located posteriorly, the soft palate is mobile and comprised of muscle fibres covered by a mucous membrane. Anteriorly, it is continuous with the hard palate and the palatine aponeurosis. The posterior border is free, and a central process, the uvula, hangs from the midline. The soft palate also forms the roof of the fauces, an area that connects the oral cavity and the pharynx.

In addition, two arches bind the palate to the tongue and pharynx. The palatoglossal arches are located anteriorly and the palatopharyngeal arches are located posteriorly. Between these two arches resides the palatine tonsils, which are found within the tonsillar fossae of the oropharynx.

The Muscles of the Soft Palate

• Tensor Veli Palatini: Originating from the medial pterygoid plate of the sphenoid, this muscle inserts into the palatine aponeurosis and is responsible for tensing the soft palate.
• Levator Veli Palatini: Starting from the petrous temporal bone and the eustachian tube, this muscle inserts into the palatine aponeurosis and is responsible for the elevation of the soft palate.
• Palatoglossus: Originating from the palatine aponeurosis, this muscle travels anteriorly, laterally and inferiorly before inserting into the side of the tongue. Its purpose is to pull the soft palate towards the tongue.
• Palatopharyngeus: This muscle arises from the palatine aponeurosis and the hard palate before inserting into the upper border of the thyroid cartilage. Its purpose is to tense the soft palate and draw the pharynx anteriorly during swallowing.
• Musculus Uvulae: This muscle arises from the posterior nasal spine and the palatine aponeurosis before inserting into the mucous membrane of the uvula. Its purpose is to shorten the uvula.

Vasculature and Innervation

The primary source of arterial supply to the palate is from the greater palatine arteries, which run anteriorly from the greater palatine foramen. Anastomosis between the lesser palatine artery and ascending palatine artery also provide collateral supply to the palate. Venous drainage is into the pterygoid venous plexus.

Sensory innervation of the palate is derived from the maxillary branch of the trigeminal nerve (CN V). The greater palatine nerve innervates most of the glandular structures of the hard palate, while the nasopalatine nerve innervates the mucous membrane of the anterior hard palate. The lesser palatine nerves innervate the soft palate.

Clinical Relevance: Cleft Lip and Cleft Palate

A cleft is a gap or split in the upper lip or palate, and can occur due to a defect during the development of the face and palate. For example, a cleft lip occurs when the medial nasal prominence and maxillary prominence fail to fuse, while a cleft palate can occur in isolation if the palatal shelves fail to fuse in the midline. This condition can also occur in combination with a cleft lip.

Cleft lip and cleft palate is relatively common, occurring in approximately 1/1000 births. In Native Americans, the rate is around 4 times that. In addition to the cosmetic and psychosocial implications, severe cleft lip/palate can be a cause of death if a baby is unable to feed. Other complications include recurrent ear infections and speech impediment.

[caption id=attachment_20670 align=aligncenter width=982] Fig 4 - Cleft palate and cleft lip.[/caption]