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Bed of tonsils medial to lateral

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"Palatine Tonsil"[MeSH Terms] AND anatomy

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Tonsil bed (tonsillar fossa), medial to lateral
  1. Tonsil with its capsule. The capsule is a fibrous hemicapsule, and the free medial surface of the tonsil faces the oropharynx.
  2. Loose areolar (peritonsillar) tissue. This is the plane of dissection in tonsillectomy. The paratonsillar (external palatine) vein runs here, and it is the usual source of post-tonsillectomy bleeding.
  3. Pharyngobasilar fascia. This is the thickened upper fascia lining the superior constrictor.
  4. Superior constrictor muscle. This is the true "bed" or floor of the fossa. The tonsillar branch of the glossopharyngeal nerve (CN IX) can be reached by separating its fibres.
  5. Buccopharyngeal fascia. This is the thin outer fascia of the pharynx.
  6. Parapharyngeal (lateral pharyngeal) space. Structures beyond the tonsil bed lie here or on its far side:
    • The tonsillar and ascending palatine branches of the facial artery pierce the constrictor to reach the tonsil.
    • The styloglossus and stylopharyngeus muscles and CN IX lie nearby.
    • The medial pterygoid muscle and the ramus of the mandible are further lateral.
    • The internal carotid artery lies about 2.5 cm posterolateral to the tonsil, so it is normally safe unless the dissection goes through the constrictor.
Boundaries of the fossa
  • Anterior: palatoglossus (palatoglossal fold).
  • Posterior: palatopharyngeus (palatopharyngeal fold).
  • Superior: soft palate.
  • Inferior: lingual tonsil.
  • Deep: superior constrictor.
These boundaries are from Pfenninger and Fowler's Procedures for Primary Care, 3rd ed., "Anatomy of the Tonsil Bed". The Scott-Brown's Otorhinolaryngology Head & Neck Surgery tonsil box describes the same location, between the palatoglossal and palatopharyngeal folds and surrounded by the capsule. I wrote the detailed layer order above from standard anatomy. I did not confirm each layer in these two texts. The layers beyond the superior constrictor (buccopharyngeal fascia, parapharyngeal space and its contents) are the part to check against your own anatomy text.
Blood supply and surgical point
  • Superior pole: ascending pharyngeal artery and lesser palatine artery.
  • Inferior pole: tonsillar branches of the facial artery, dorsal lingual artery and ascending palatine artery.
  • The tonsillar artery from the facial artery is the dominant supply.
  • Venous drainage is through the paratonsillar vein.
  • Lymph drains to the jugulodigastric node.
  • For brisk bleeding from the bed, control the superior and inferior poles first, because they are where the vessels enter (Pfenninger and Fowler's).
Recent evidence check: My PubMed search for recent reviews on tonsil anatomy returned nothing relevant (results were on cerebellar tonsils and palatal shape). I found no recent evidence that changes this answer.

Short

Tonsil bed, medial to lateral
  1. Tonsil with its capsule
  2. Loose areolar (peritonsillar) tissue, which holds the paratonsillar vein
  3. Pharyngobasilar fascia
  4. Superior constrictor muscle (the true floor of the bed)
  5. Buccopharyngeal fascia
  6. Parapharyngeal space. It contains the facial artery branches, CN IX, and the styloglossus and stylopharyngeus. Beyond it are the medial pterygoid and the mandibular ramus. The internal carotid artery lies about 2.5 cm posterolateral.
Boundaries
  • Anterior: palatoglossus
  • Posterior: palatopharyngeus
  • Superior: soft palate
  • Inferior: lingual tonsil
I took the boundaries from Pfenninger and Fowler's Procedures for Primary Care, 3rd ed. I wrote the layer order from standard anatomy and did not verify each layer in the textbooks.
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