Head and neck anatomy

Cranial nerves at the bedside

• Lacrimation pathway: superior salivatory nucleus, facial nerve, greater petrosal nerve (preganglionic parasympathetic), nerve of the pterygoid canal, pterygopalatine ganglion, then zygomatic and lacrimal nerves. A facial lesion proximal to the geniculate ganglion gives a dry eye.
• Bulbar palsy (LMN: wasted fasciculating tongue) versus pseudobulbar palsy (UMN: spastic tongue, brisk jaw jerk, emotional lability).
• Horner syndrome: partial ptosis, miosis, anhidrosis; Pancoast tumour, carotid dissection, lateral medullary syndrome, neck surgery.
• Cavernous sinus: III, IV, V1, V2 in the lateral wall; VI and the internal carotid artery inside the sinus, so VI is affected first.

Visual pathway lesions

Neck triangles, vessels and airway

• Posterior triangle (sternocleidomastoid, trapezius, clavicle): roof of investing fascia; floor of muscles covered by prevertebral fascia (splenius, levator scapulae, scalenes). The accessory nerve runs superficially across it, just under the investing layer, so it is easily cut in node biopsy. Other contents: brachial plexus trunks, subclavian artery, external jugular vein, and the transverse cervical and suprascapular arteries, branches of the thyrocervical trunk (from the first part of the subclavian artery).
• Carotid sheath: common carotid medial, internal jugular vein lateral, vagus behind between them; bifurcation at the upper border of the thyroid cartilage (C3–C4).
• Compressing the common carotid: press backwards against the anterior (carotid) tubercle of the C6 transverse process, the most prominent cervical tubercle, at the level of the cricoid. The first rib is the landmark for the subclavian artery, not the carotid.
• Carotid sinus massage stretches the baroreceptors, increasing their firing; the glossopharyngeal afferents raise vagal (parasympathetic) output and slow the heart, which can end a supraventricular tachycardia. Avoid it in elderly patients with bruits.
• Internal jugular cannulation: apex of the triangle between the two heads of sternocleidomastoid and the clavicle, lateral to the carotid pulse, aiming at the ipsilateral nipple; right side preferred. Risks: carotid puncture, pneumothorax, air embolism. Subclavian route carries the highest pneumothorax risk and lowest infection risk.
• Cricothyroidotomy goes through the avascular cricothyroid membrane; tracheostomy through rings 2–4 (thyroid isthmus overlies them).
• Larynx: all intrinsic muscles are supplied by the recurrent laryngeal nerve except cricothyroid (external laryngeal nerve). Posterior cricoarytenoid is the only abductor. The left RLN hooks under the aortic arch (affected by lung cancer, aneurysm, enlarged left atrium).
• Pharyngeal pouch (Zenker diverticulum): arises posteriorly through Killian dehiscence, the weak area between the thyropharyngeal and cricopharyngeal parts of the inferior constrictor. Elderly patient with dysphagia, regurgitation of undigested food, halitosis and a gurgling neck swelling.

Thyroid: nodules and surgical anatomy

• Solitary nodule in a euthyroid patient (normal TSH): next step is ultrasound with FNAC. Isotope scanning is used when TSH is low, to look for a hot nodule.
• Toxic multinodular goitre: elderly patient with long-standing goitre who becomes thyrotoxic; scan shows several hot nodules with suppressed uptake elsewhere (Graves disease shows diffuse uptake; a single hot nodule is a toxic adenoma).
• Recurrent laryngeal nerve at thyroidectomy: most at risk at the ligament of Berry, where the gland is attached to the trachea and the nerve runs close to or through it. The tubercle of Zuckerkandl, a posterolateral projection of the lobe at the level of the cricoid, has the RLN deep to it, so it is a reliable guide. A non-recurrent right laryngeal nerve occurs with an aberrant right subclavian artery.
• External laryngeal nerve runs with the superior thyroid artery; injury weakens high-pitched voice.

Exam trap Stridor hours after thyroidectomy with a swelling neck is haematoma: open the wound before anything else.

Spine, vertebral joints and the spinal needle

• Atlanto-occipital joint allows nodding (flexion and extension); the atlanto-axial joint is a pivot joint (dens in the ring of the atlas) and allows rotation, as when looking left and right. Atlanto-axial instability occurs in rheumatoid arthritis and Down syndrome.
• Eight cervical nerves: C1–C7 exit above their vertebrae, C8 below C7, and all lower nerves exit below theirs.
• Spinal cord ends at L1–L2 in adults (L3 at birth); the dural sac ends at S2.
• Sacral hiatus results from failure of fusion of the laminae of S5 (sometimes S4), bounded by the sacral cornua. Because it lies below the dural sac, a caudal block injects into the epidural space, not the subarachnoid space.
• Lumbar puncture: at L3/L4 or L4/L5, below the cord; the line joining the iliac crests (Tuffier line) crosses L4. The patient lies on the side with knees to chest, because flexion separates the spinous processes and opens the gaps between the laminae.
• Layers crossed: skin, fat, supraspinous ligament, interspinous ligament, ligamentum flavum (loss of resistance), epidural space, dura, arachnoid, then CSF.
• Image the brain first if there are focal signs, papilloedema, seizures or reduced consciousness (risk of coning). Post-dural puncture headache is postural; pencil-point needles reduce it; an epidural blood patch treats it. Normal opening pressure is about 10–20 cmH2O.

Remember Cord ends L1–L2, sac ends S2, needle goes in at L3/L4 or L4/L5.

Cord syndromes and compression

• Disc prolapse is commonest at L4/L5 and L5/S1 and compresses the traversing (lower) root.
• Metastatic cord compression (breast, lung, prostate, kidney, myeloma; thoracic spine commonest): back pain worse lying down, leg weakness, sensory level, sphincter upset; give dexamethasone, arrange urgent whole-spine MRI, then radiotherapy or decompression.

How FCPS asks about this

• Common carotid compressed against: anterior (carotid) tubercle of C6.
• Floor of the posterior triangle and the nerve at risk: muscles covered by prevertebral fascia; superficial accessory nerve.
• Where the RLN is most at risk at thyroidectomy: ligament of Berry; it lies deep to the tubercle of Zuckerkandl.
• Stridor and neck swelling two hours after thyroidectomy: open the wound at the bedside; perioral tingling on day 2 means hypocalcaemia, check calcium.
• Pharyngeal pouch origin: Killian dehiscence in the inferior constrictor.
• Sacral hiatus: failure of fusion of S5 laminae; caudal block is epidural because the dural sac ends at S2.
• Parasympathetic supply for lacrimation: greater petrosal nerve to the pterygopalatine ganglion; rotation of the head occurs at the pivot atlanto-axial joint.