What is Retromolar Trigone – Anatomy, Boundaries and Importance

Retromolar Trigone (rTR) is the Gingiva or mucosa covering the alveolar ridge posterior to the last Mandibular molar overlying the ramus of the mandible and is defined as a Roughly triangular space. The mucosa covering the Retromolar Trigone is rigid as it is tightly adherent to the underlying alveolar bone. This is what is said to help malignant tumors infiltrate the mandible in a short period if time in the early stages. The rTR is known as the anatomic crossroad where muscular and nervous components converge.

The Lingual nerve is also positioned behind the Retromoalr trigone and medially placed which is the reason why the Lingual nerve involvement is seen in Cancers of Retromolar Trigone. As it shares the borders with many vital structures like the tonsils, tongue, floor of mouth and soft palate, in case of any cancer involving Retromolar Trigone all these structures have a high chance of being invaded by the cancer. The tumors from the surrounding structures frequently extend into the Trigone making it difficult to determine the source of the tumor.

What is Retromolar Trigone – Anatomy, Boundaries and Importance

Image Source: https://www.ncbi.nlm.nih.gov/books/NBK65887/figure/CDR0000258017__308/

Boundries of Retromolar Trigone:

  • Anterior base is posterior to the last molar.
  • Superior end is the maxillary tuberosity
  • Buccaly or laterally it is lined by the oblique line of the mandible extending up to the coronoid process
  • Medial border extends between the distolingual cusp of the last molar to the coronoid process.

The small triangular area is covered laterally by the buccal mucosa and medially by the anterior tonsillar pillar. The buccinator muscle anteriolaterally and masseter muscle on the posteriolateral side are the anatomic muscle relationships of the Trigone.

Nerve Supply to Retromolar Trgione:

  • Branches of the Glossopharyngeal and lesse palatine nerves (V2)

Blood Supply to Retromolar Trigone:

  • Tonsillar and Ascending palatine branches of the facial artery – major contribution
  • Dorsal lingual, ascending pharyngeal and lesser palatine arteries.

Venous and Lymphatic drainage of Retromolar Trigone:

  • Venous drainage is to the pharyngeal plexus and common facial vein
  • Lymphatic drainage is to the upper deep jugular chain

Retromolar Trigone cancers are seen to extend to surrounding muscles, adipose spaces, soft palate, tonsillar fossa, pharyngeal space and the floor of the mouth.

Diagnostic methods to detect Retromolar Trigone Cancer, Cyst or Tumors are Computed Tomography – multidetector CT has been found to be useful in providing better anatomic resolution with options like “puffed-cheek distension”.

Cancer of Retromolar Trigone:

Most common type of Cancer seen is the Squamous cell carcinoma in different grades of differentiation. The tumours of the rTR are mucosal neoplasms of gums and cheek which constitute almost 12% of the oral tumors. The other types of less commonly used cancers involving rTR are – mucoepidermoid carcinoma, cystic adenoid carcinoma, adenoidcarcinoma.

The progression of Malignancy is rapid in case of tumors involving rTR and the real extent is underestimated during clinical examination, due to which the prognosis is bad compared to other neoplasms of oral cavity. The most common symptoms or rTR cancer are – Trismus, Trigeminal anesthesia, neuralgia, otalgia.


Sceincedirect – Diagnostic Approach to Retromolar Trigone Cancer by Multiplanar Computed Tomography Reconstructions

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