Basic Sciences Relevant to ENT
Core rules
The temporal bone contains the facial nerve in labyrinthine, tympanic and mastoid segments; the labyrinthine segment is the narrowest and most vulnerable to edema. The recurrent laryngeal nerve runs in the tracheoesophageal groove and is at risk in thyroid surgery; the external branch of the superior laryngeal nerve supplies cricothyroid. Paranasal sinus drainage follows the ostiomeatal complex for anterior sinuses and the sphenoethmoidal recess for posterior sinuses. Microbiology of CSOM commonly involves Pseudomonas aeruginosa and Staphylococcus aureus; acute pharyngitis is often viral or Streptococcus pyogenes. Pharmacology: aminoglycosides are ototoxic and nephrotoxic; corticosteroids reduce inflammation but have systemic effects. Immunology: allergic rhinitis is a type I IgE-mediated hypersensitivity. Pathology: squamous cell carcinoma is the commonest head and neck malignancy, while pleomorphic adenoma is the commonest benign salivary tumor.
Worked example
A patient develops hoarseness after thyroidectomy. The recurrent laryngeal nerve is the likely injured structure because it traverses the tracheoesophageal groove. Laryngoscopy confirms vocal fold paresis. This anatomy explains the surgical risk and the need for nerve identification.
Traps
Do not confuse the facial nerve segments or their surgical landmarks. Do not overlook aminoglycoside ototoxicity. Do not assume all head and neck masses are squamous carcinoma. Do not confuse type I and type IV hypersensitivity.