AP: Head, neck and back anatomy

• Head: The Skull and Scalp | Meninges and Intracranial Haemorrhage | Blood Supply of the Brain | The Cranial Nerves | The Face and Trigeminal Nerve | The Facial Nerve
• Neck: Triangles of the Neck | Larynx, Thyroid and Neck Structures | Vessels and Lymph Nodes of the Neck | Lower Cranial Nerves in the Neck
• Back: The Vertebral Column | The Spinal Cord and Its Blood Supply | Cord Lesions and Back Pain | Lumbar Puncture and Epidural Anatomy
• Revision: Head, Neck and Back at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🧠 Head, neck and back anatomy — page 6 of the Anatomy and Physiology chapter. This region holds the brain, the airway, the great vessels and the spinal cord, packed into a small space — so small lesions cause big problems. Head injuries, strokes, cranial nerve palsies, neck lumps, airway procedures, cord compression and lumbar puncture all depend on knowing what lies where.
Your four questions for every head, neck or back problem: Which cranial nerve, vessel or spinal level is involved? What lies next to it — and could be compressed or damaged? Is there a danger to the airway, the brain or the cord? Which landmark guides the procedure safely?

The Skull and Scalp

• Skull — neurocranium (vault and base — protects the brain) and viscerocranium (facial skeleton); 22 bones (excluding ossicles).
• Sutures — coronal (frontal–parietal), sagittal (between parietals), lambdoid (parietal–occipital); fontanelles in infants — anterior (closes by about 18 months — bulging in raised ICP, sunken in dehydration) and posterior (closes by about 2 months); craniosynostosis (premature fusion).
• Pterion — the H-shaped junction of the frontal, parietal, temporal and sphenoid bones (about 3 cm above the zygomatic arch) — thinnest part of the skull; the middle meningeal artery runs beneath it → extradural haematoma after a blow to the side of the head.
• Cranial fossae (base) — anterior (frontal lobes; cribriform plate — olfactory nerves), middle (temporal lobes; pituitary in the sella turcica), posterior (cerebellum, brainstem; foramen magnum).
• Key foramina:

  Foramen	Contents
  Cribriform plate	Olfactory nerves (I) — fracture → anosmia, CSF rhinorrhoea
  Optic canal	Optic nerve (II), ophthalmic artery
  Superior orbital fissure	III, IV, V1, VI, ophthalmic veins
  Foramen rotundum	V2 (maxillary)
  Foramen ovale	V3 (mandibular)
  Foramen spinosum	Middle meningeal artery
  Internal acoustic meatus	VII, VIII (vestibular schwannoma)
  Jugular foramen	IX, X, XI, internal jugular vein
  Hypoglossal canal	XII
  Foramen magnum	Medulla, vertebral arteries, spinal accessory roots — tonsillar herniation (coning)

  "Standing Room Only" — superior orbital fissure, rotundum, ovale for V1, V2, V3.
• Basal skull fracture signs — periorbital bruising ("panda eyes"), Battle's sign (mastoid bruising — late), haemotympanum, CSF rhinorrhoea or otorrhoea — CT head; avoid nasal tubes.
• Scalp layers — "SCALP" — Skin, Connective tissue (dense — vessels held open → scalp wounds bleed heavily), Aponeurosis (galea), Loose areolar tissue (the "danger layer" — emissary veins can carry infection inside the skull; subgaleal haematoma), Pericranium.

Meninges and Intracranial Haemorrhage

• Meninges — dura mater (tough, outer — two layers that separate to form the venous sinuses; folds — falx cerebri, tentorium cerebelli), arachnoid mater, pia mater (on the brain surface).
• CSF — produced by the choroid plexus (about 500 mL a day; about 150 mL present) → lateral ventricles → foramina of Monro → third ventricle → cerebral aqueduct → fourth ventricle → foramina of Luschka and Magendie → subarachnoid space → absorbed by arachnoid granulations into the dural venous sinuses.
• Hydrocephalus — obstructive (non-communicating) (aqueduct stenosis, tumours, colloid cyst) vs communicating (impaired absorption — after SAH or meningitis; normal pressure hydrocephalus — triad of gait apraxia, urinary incontinence and dementia).
• Intracranial haemorrhage by space:

  Type	Vessel	CT appearance	Clinical features
  Extradural	Middle meningeal artery (pterion fracture)	Biconvex (lentiform); doesn't cross sutures	Young; head injury, lucid interval, then rapid deterioration — urgent evacuation
  Subdural	Bridging veins (cortex to sinuses)	Crescent-shaped; crosses sutures, not the midline	Older people, alcohol, anticoagulants; acute (trauma) or chronic (weeks — fluctuating confusion, headache)
  Subarachnoid	Berry aneurysm (circle of Willis) or trauma	Blood in the sulci and basal cisterns	Thunderclap headache, neck stiffness, collapse
  Intracerebral	Small penetrating arteries (hypertension), amyloid angiopathy	Blood within the brain (basal ganglia, lobar)	Stroke symptoms, headache, vomiting

• Dural venous sinuses — superior sagittal → transverse → sigmoid → internal jugular vein; cavernous sinus (beside the pituitary) contains the internal carotid artery and CN VI in the sinus, with III, IV, V1 and V2 in its lateral wall → cavernous sinus thrombosis (from facial infection — "danger triangle" of the face) → ophthalmoplegia, proptosis, chemosis.
• Venous sinus thrombosis — headache, seizures, papilloedema, focal signs — OCP, pregnancy, dehydration, thrombophilia — CT or MR venogram — anticoagulation.
• Brain herniation — subfalcine (under the falx), uncal (transtentorial) (temporal lobe compresses CN III — fixed dilated pupil — and the cerebral peduncle), tonsillar (cerebellar tonsils through the foramen magnum — compresses the medulla — respiratory arrest; why LP is dangerous with raised ICP).

Blood Supply of the Brain

• Anterior circulation — internal carotid arteries → ophthalmic artery (amaurosis fugax), anterior cerebral artery (ACA) and middle cerebral artery (MCA).
• Posterior circulation — vertebral arteries (through the transverse foramina of C6–C1) → join to form the basilar artery (on the pons) → posterior cerebral arteries (PCA); branches to the cerebellum (PICA, AICA, SCA) and brainstem.
• Circle of Willis — anastomosis at the base of the brain linking anterior and posterior circulations (anterior and posterior communicating arteries) — collateral flow; berry aneurysms at junctions (anterior communicating commonest; posterior communicating aneurysm compresses CN III — painful third nerve palsy with a dilated pupil).
• Territories and stroke syndromes:

  Artery	Territory	Stroke features
  ACA	Medial frontal and parietal lobes	Contralateral leg weakness and sensory loss more than arm; personality change, incontinence
  MCA	Lateral hemisphere, internal capsule	Contralateral face and arm more than leg weakness and sensory loss, homonymous hemianopia; aphasia (dominant — usually left) or neglect (non-dominant)
  PCA	Occipital lobe, thalamus	Contralateral homonymous hemianopia with macular sparing; visual agnosia
  PICA (or vertebral)	Lateral medulla	Lateral medullary (Wallenberg) syndrome — ipsilateral facial pain/temperature loss, Horner's, ataxia, dysphagia; contralateral body pain/temperature loss; vertigo
  Basilar	Pons, brainstem	Locked-in syndrome, coma, quadriplegia, cranial nerve palsies
  Lenticulostriate	Internal capsule, basal ganglia	Lacunar — pure motor, pure sensory, ataxic hemiparesis (hypertension, diabetes)

• Venous drainage — cerebral veins → dural venous sinuses → internal jugular veins.
• Autoregulation — cerebral blood flow kept constant (about 50 mL/100 g/min) over a MAP of about 60–150 mmHg; lost in brain injury; CO₂ dilates cerebral vessels (hypercapnia raises ICP).
• Blood–brain barrier — tight junctions of capillary endothelium with astrocyte foot processes — limits entry of drugs (lipid-soluble pass); absent in circumventricular organs (area postrema — vomiting centre).

The Cranial Nerves

• Brainstem levels — midbrain (III, IV), pons (V, VI, VII, VIII), medulla (IX, X, XI, XII) — "2 above the pons, 4 in the pons, 4 in the medulla".
• Eye movements — "LR6 SO4" — lateral rectus by VI, superior oblique by IV, all others by III.
• Bulbar vs pseudobulbar palsy — bulbar (LMN — IX, X, XII — wasted fasciculating tongue, absent gag, nasal speech — MND, GBS, myasthenia) vs pseudobulbar (UMN — bilateral corticobulbar — spastic tongue, brisk jaw jerk, emotional lability — bilateral strokes, MS, MND).
• Multiple cranial nerve palsies — cavernous sinus (III, IV, V1, V2, VI), cerebellopontine angle (V, VII, VIII — vestibular schwannoma), jugular foramen (IX, X, XI), basal meningitis, sarcoidosis, nasopharyngeal carcinoma.

The Face and Trigeminal Nerve

• Trigeminal nerve (V) — the main sensory nerve of the face:
  • V1 Ophthalmic — forehead, upper eyelid, cornea (corneal reflex), tip of the nose (Hutchinson's sign — nasal tip vesicles in shingles predict eye involvement).
  • V2 Maxillary — cheek, lower eyelid, upper lip, upper teeth, maxillary sinus.
  • V3 Mandibular — lower lip, chin, lower teeth, anterior two-thirds of the tongue (general sensation), temple; motor to the muscles of mastication (masseter, temporalis, pterygoids).
  • The angle of the jaw is supplied by C2–3 (great auricular nerve), not V — non-organic facial sensory loss often includes it.
• Trigeminal neuralgia — brief, severe, electric shock-like pain (usually V2/V3) triggered by touching, chewing or shaving — carbamazepine first line; MRI (compression by a vessel; MS in young people).
• Muscles of facial expression — supplied by the facial nerve (VII); orbicularis oculi (eye closure), orbicularis oris, buccinator, frontalis, platysma.
• Parotid gland — in front of the ear; the facial nerve passes through it (divides into 5 branches — "To Zanzibar By Motor Car" — Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical); parotid duct (Stensen's) opens opposite the upper second molar; secretomotor supply via CN IX.
• Parotid tumours — mostly benign (pleomorphic adenoma); facial nerve palsy suggests malignancy; facial nerve at risk in parotidectomy.
• Submandibular gland — duct (Wharton's) opens beside the frenulum — stones (swelling with eating); marginal mandibular nerve at risk in surgery (lip weakness).
• Facial arteries and veins — the facial artery crosses the mandible in front of masseter (palpable pulse); facial veins connect with the cavernous sinus — the "danger triangle" (nose and upper lip) — infection can spread intracranially.
• Temporomandibular joint — dislocation (anterior — can't close the mouth), TMJ dysfunction (clicking, pain); jaw jerk (V3 — brisk in UMN lesions above the pons).
• Orbit — blowout fracture of the orbital floor (inferior rectus entrapment — can't look up; infraorbital nerve numbness — V2).

The Facial Nerve

• Course — pons → cerebellopontine angle → internal acoustic meatus (with VIII) → facial canal in the temporal bone (geniculate ganglion — branches: greater petrosal — lacrimation; nerve to stapedius; chorda tympani — taste to the anterior two-thirds of the tongue and submandibular/sublingual salivation) → stylomastoid foramen → parotid gland → 5 terminal motor branches.
• UMN vs LMN facial weakness:
  • UMN lesion (stroke, tumour) — forehead spared (upper face has bilateral cortical supply) — contralateral weakness of the lower face.
  • LMN lesion (Bell's palsy, parotid tumour, Ramsay Hunt) — whole half of the face on the same side, including the forehead; can't close the eye (corneal exposure).
• Localising a LMN lesion — loss of taste (chorda tympani) and hyperacusis (stapedius) mean a lesion within the facial canal; parotid lesions spare these.
• Bell's palsy — idiopathic LMN facial palsy, onset over 72 hours or less — prednisolone within 72 hours; eye protection (lubricants, tape at night); most recover within 3–6 months.
• Ramsay Hunt syndrome — herpes zoster of the geniculate ganglion — facial palsy, painful vesicles in the ear canal and on the palate, hearing loss and vertigo — aciclovir and steroids; worse prognosis.
• Other causes — Lyme disease (bilateral), Guillain–Barré (bilateral), sarcoidosis (bilateral — with parotid swelling), cholesteatoma and middle ear infection, temporal bone fracture, parotid tumours, HIV, pregnancy, diabetes.
• Bilateral facial palsy — think Lyme, GBS, sarcoid (rarely bilateral Bell's).

Triangles of the Neck

• Sternocleidomastoid (SCM) divides the neck into the anterior and posterior triangles; it turns the head to the opposite side and is supplied by CN XI.
• Anterior triangle — boundaries: anterior border of SCM, midline of the neck, lower border of the mandible.
  • Contents — carotid arteries (carotid sheath), internal jugular vein, CN IX, X, XII, larynx, trachea, thyroid and parathyroids, submandibular gland, lymph nodes.
  • Sub-triangles — submental, submandibular (digastric), carotid (carotid bifurcation — at the upper border of the thyroid cartilage, C3/4), muscular.
• Posterior triangle — boundaries: posterior border of SCM, anterior border of trapezius, middle third of the clavicle.
  • Contents — accessory nerve (XI) (superficial — injured in lymph node biopsy → weak shoulder shrug, winging), roots and trunks of the brachial plexus, subclavian artery (third part), external jugular vein, cervical plexus branches (great auricular, lesser occipital, transverse cervical, supraclavicular nerves — emerge at Erb's point), phrenic nerve on scalenus anterior, lymph nodes.
• Carotid sheath — contains the common/internal carotid artery (medial), internal jugular vein (lateral) and vagus nerve (posterior, between them); deep cervical lymph nodes along the IJV; the sympathetic chain lies behind the sheath.
• Neck lumps by site:

  Site	Causes
  Midline	Thyroglossal cyst (moves up on tongue protrusion), thyroid isthmus nodule (moves on swallowing), dermoid cyst, lymph node (submental)
  Anterior triangle	Lymph nodes (commonest), branchial cyst (anterior border of SCM, young adult), carotid body tumour (pulsatile, moves side to side not up and down), salivary gland, thyroid lobe, laryngocele
  Posterior triangle	Lymph nodes (lymphoma, TB, metastases, EBV), cystic hygroma (infants — transilluminates), cervical rib
  Supraclavicular	Virchow's node (left — gastric and abdominal malignancy), lung, breast and lymphoma

• Red flags in a neck lump — age over 45, persistent over 3 weeks, hard, fixed, growing, with hoarseness, dysphagia, weight loss or night sweats — 2-week-wait head and neck referral (or haematology).

Larynx, Thyroid and Neck Structures

• Vertebral levels in the neck:
  • C2/3 — hyoid bone (C3).
  • C4 — upper border of the thyroid cartilage — carotid bifurcation (C3/4).
  • C6 — cricoid cartilage — start of the trachea and oesophagus; middle cervical ganglion; vertebral artery enters the transverse foramen.
  • C7 — vertebra prominens.
• Larynx — thyroid cartilage (Adam's apple), cricoid cartilage (complete ring — cricoid pressure), arytenoids, epiglottis; cricothyroid membrane between the thyroid and cricoid cartilages — emergency front-of-neck access (cricothyroidotomy) — below the vocal cords and above the thyroid isthmus.
• Vocal cord nerves — recurrent laryngeal nerve (all intrinsic laryngeal muscles except cricothyroid — unilateral palsy → hoarse, breathy voice; bilateral → stridor) and the external branch of the superior laryngeal nerve (cricothyroid — high-pitched voice, e.g. singers after thyroidectomy).
• Thyroid gland:
  • Two lobes joined by an isthmus over the 2nd–4th tracheal rings; enclosed in pretracheal fascia — moves up on swallowing.
  • Blood supply — superior thyroid artery (external carotid — near the external branch of the superior laryngeal nerve), inferior thyroid artery (thyrocervical trunk — closely related to the recurrent laryngeal nerve), occasional thyroidea ima (midline — tracheostomy risk).
  • Development — from the foramen caecum at the base of the tongue, descending along the thyroglossal duct (ectopic lingual thyroid, thyroglossal cyst, pyramidal lobe).
  • Thyroidectomy complications — bleeding (neck haematoma — airway compression), recurrent laryngeal nerve palsy, hypocalcaemia (parathyroid damage — tingling, tetany within 24–48 hours), hypothyroidism.
• Parathyroid glands — usually 4, on the posterior thyroid; inferior glands develop from the 3rd pharyngeal pouch (with the thymus — may be ectopic in the mediastinum), superior from the 4th.
• Trachea — C6 to T4/5 (carina); tracheostomy through the 2nd–4th rings (below the cricoid).
• Oesophagus — begins at C6 behind the trachea; Zenker's (pharyngeal pouch) diverticulum through Killian's dehiscence (above cricopharyngeus) — dysphagia, regurgitation, halitosis, gurgling neck lump.
• Fascial spaces of the neck — infections can spread from the teeth and pharynx through the retropharyngeal and parapharyngeal spaces into the mediastinum (descending mediastinitis); Ludwig's angina (floor of the mouth — airway emergency).

Vessels and Lymph Nodes of the Neck

• Common carotid artery — divides at C3/4 (upper border of the thyroid cartilage) into:
  • Internal carotid — no branches in the neck; enters the skull through the carotid canal; carotid sinus (baroreceptors — CN IX) at its origin; carotid body (chemoreceptors).
  • External carotid — branches supply the neck and face: "Some Anatomists Like Freaking Out Poor Medical Students" — superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, maxillary (→ middle meningeal), superficial temporal (temporal arteritis).
• Carotid disease — atherosclerosis at the bifurcation → TIA and stroke, amaurosis fugax — carotid endarterectomy for symptomatic stenosis of 50–99% (NASCET); carotid bruit; carotid dissection (neck pain, Horner's, stroke — after neck trauma or manipulation).
• Carotid sinus hypersensitivity — syncope with neck pressure (shaving, tight collars) — older men; carotid sinus massage (contraindicated with bruits or recent stroke).
• Subclavian artery — branches: vertebral, internal thoracic (mammary — used for CABG), thyrocervical trunk, costocervical trunk.
• Veins — internal jugular vein (from the jugular foramen in the carotid sheath — JVP is assessed from the right IJV between the heads of SCM; central lines) and external jugular vein (superficial over SCM — visible, but less reliable for the JVP).
• JVP — vertical height above the sternal angle (normal under 3–4 cm) with the patient at 45°; raised in right heart failure, fluid overload, tricuspid regurgitation (giant v waves), constrictive pericarditis (Kussmaul's sign), SVC obstruction (non-pulsatile).
• Cervical lymph node levels (I–VI) — I submental and submandibular, II–IV along the IJV (upper, middle, lower deep cervical — jugulodigastric node at level II drains the tonsil), V posterior triangle, VI central (around the thyroid and larynx).
• Lymphatic drainage — all head and neck lymph eventually passes through the deep cervical nodes along the IJV → jugular trunk → thoracic duct (left) or right lymphatic duct.

Lower Cranial Nerves in the Neck

• Glossopharyngeal (IX) — leaves through the jugular foramen; sensation to the pharynx and posterior tongue (afferent limb of the gag reflex), taste to the posterior third, carotid sinus and body, parotid secretion.
• Vagus (X) — jugular foramen → in the carotid sheath → thorax and abdomen:
  • Branches — pharyngeal (palate and pharynx), superior laryngeal (internal — sensation above the cords; external — cricothyroid), recurrent laryngeal (right — around the subclavian artery; left — around the aortic arch), cardiac, pulmonary, oesophageal, gastric.
  • Lesion — palate drops on the affected side; uvula deviates to the healthy side; hoarse voice; dysphagia; reduced cough.
  • Vagal stimulation — vasovagal syncope, bradycardia (carotid sinus massage, Valsalva), Arnold's (auricular) branch — cough on ear syringing.
• Accessory (XI) — spinal roots rise through the foramen magnum and leave through the jugular foramen → SCM → crosses the posterior triangle superficially → trapezius.
• Hypoglossal (XII) — hypoglossal canal → loops forward below the digastric muscle, crossing the carotid arteries → tongue muscles; injured in carotid endarterectomy and submandibular surgery.
• Sympathetic chain — behind the carotid sheath; superior (C1–2 — Horner's from carotid dissection), middle (C6) and inferior (stellate with T1) cervical ganglia; stellate ganglion block (complex regional pain syndrome, refractory arrhythmias).
• Phrenic nerve (C3–5) — on the anterior surface of scalenus anterior (deep to the prevertebral fascia) → thorax — blocked by interscalene brachial plexus blocks (hemidiaphragm paralysis).
• Cervical plexus (C1–4) — sensory to the neck and back of the scalp (great auricular — angle of jaw and ear; lesser occipital); motor — ansa cervicalis (strap muscles), phrenic contribution.
• Swallowing — oral (voluntary — V, VII, XII) → pharyngeal (reflex — IX, X; larynx elevates, epiglottis closes, cords adduct) → oesophageal (peristalsis — X); dysphagia after stroke (bulbar weakness) — formal swallow assessment before oral intake (aspiration risk).

The Vertebral Column

• Vertebrae — 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused — sacrum), 4 coccygeal (fused); curvatures — cervical and lumbar lordosis, thoracic and sacral kyphosis.
• Typical vertebra — body, vertebral arch (pedicles and laminae), spinous process, transverse processes, articular processes (facet joints); intervertebral foramina transmit spinal nerves.
• Regional features:
  • Cervical — small bodies, transverse foramina (vertebral arteries — C6 to C1), bifid spinous processes; C1 atlas (no body — "yes" nodding), C2 axis (dens/odontoid peg — "no" rotation — atlanto-axial joint).
  • Thoracic — articulate with ribs (costal facets); long downward-sloping spinous processes; relatively immobile.
  • Lumbar — large bodies; most disc prolapses and degeneration at L4/5 and L5/S1.
• Intervertebral discs — outer annulus fibrosus (fibrocartilage) and inner nucleus pulposus (gel) — prolapse is usually posterolateral (posterior longitudinal ligament is narrow and strongest in the midline).
• Ligaments — anterior and posterior longitudinal ligaments, ligamentum flavum (between laminae — "pop" felt during epidural insertion), interspinous and supraspinous ligaments.
• Spinal nerves — 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal):
  • Cervical nerves exit above their vertebra (C1–C7), C8 exits below C7; thoracic and lumbar nerves exit below their vertebra.
  • A C5/6 disc compresses the C6 root; an L4/5 disc (posterolateral) compresses L5.
• Atlanto-axial instability — rheumatoid arthritis, Down syndrome — risk during intubation (neck extension) — flexion–extension X-rays.
• Cervical spine injury — NEXUS or Canadian C-spine rule decide imaging (CT for adults per NICE NG232); C1 (Jefferson — burst), C2 (hangman's, odontoid peg) fractures.
• Ankylosing spondylitis — fused, brittle spine ("bamboo spine") — fractures after minor trauma; osteoporotic vertebral fractures (thoracic — kyphosis, height loss); spondylolisthesis (slip of one vertebra on another — L5/S1).

The Spinal Cord and Its Blood Supply

• Spinal cord — from the medulla at the foramen magnum to the conus medullaris at L1/2 in adults (L3 at birth); enlargements at C5–T1 (arms) and L1–S3 (legs); below the conus, the nerve roots form the cauda equina; filum terminale anchors it to the coccyx.
• Vertebral vs cord segments — the cord is shorter than the canal, so cord segments lie higher than the matching vertebrae (e.g. a T10 vertebral fracture may damage lumbar cord segments).
• Cross-section — central grey matter (H-shaped — dorsal horns sensory, ventral horns motor, lateral horns T1–L2 sympathetic) surrounded by white matter tracts.
• Main tracts:
  • Dorsal columns — vibration and proprioception (ipsilateral in the cord).
  • Lateral corticospinal tract — voluntary movement (ipsilateral in the cord — crossed in the medulla).
  • Spinothalamic tract (anterolateral) — pain and temperature (contralateral — crossed near entry).
• Blood supply:
  • One anterior spinal artery (from the vertebral arteries) — supplies the anterior two-thirds of the cord (corticospinal and spinothalamic tracts, anterior horns).
  • Two posterior spinal arteries — supply the posterior third (dorsal columns).
  • Segmental (radicular) arteries reinforce them — the largest is the artery of Adamkiewicz (usually left, T9–T12) — at risk in thoracoabdominal aortic aneurysm repair and dissection → anterior spinal artery syndrome (paraplegia).
  • Watershed zone — mid-thoracic cord (T4–T8) — vulnerable to hypotension.
• Venous drainage — internal and external vertebral venous plexuses (Batson's plexus — valveless, linking pelvic and vertebral veins → spread of prostate, breast and other cancers to the spine).

Cord Lesions and Back Pain

• Spinal cord syndromes:

  Syndrome	Cause	Features
  Complete transection	Trauma, tumour, transverse myelitis	Loss of all motor and sensory function below the level; bladder and bowel; spinal shock initially
  Anterior cord	Anterior spinal artery occlusion (aortic surgery, dissection), flexion injury	Paralysis and loss of pain and temperature below the level; dorsal columns spared (vibration and proprioception preserved)
  Central cord	Hyperextension in older people with cervical spondylosis; syringomyelia	Arms weaker than legs (central fibres for the arms); variable sensory loss; "cape" loss in syrinx
  Brown-Séquard	Penetrating injury, tumour, MS	Ipsilateral weakness and loss of vibration/proprioception; contralateral pain and temperature loss
  Posterior cord	B12 deficiency, syphilis (tabes), nitrous oxide	Loss of vibration and proprioception — sensory ataxia, positive Romberg
  Conus medullaris	Disc, tumour, trauma at L1	Early sphincter dysfunction, saddle anaesthesia, mixed UMN and LMN signs
  Cauda equina	Central disc prolapse, tumour, abscess	Asymmetrical LMN leg weakness, saddle anaesthesia, sciatica, sphincter dysfunction

• Metastatic spinal cord compression — known cancer (breast, lung, prostate, kidney, myeloma) with new back pain (especially thoracic, night pain, worse lying flat), then weakness, sensory level, sphincter problems — MRI whole spine within 24 hours (immediately if neurological signs), dexamethasone 16 mg, flat if unstable, radiotherapy or surgery (NICE NG234).
• Spinal cord injury levels — C3–5 (diaphragm — ventilation), above T6 (autonomic dysreflexia), neurogenic shock (hypotension and bradycardia — loss of sympathetic outflow above T6).
• Back pain red flags — age under 20 or over 55 (new), history of cancer, weight loss, fever and IV drug use or immunosuppression (infection — discitis, epidural abscess), trauma (or minor trauma with osteoporosis), thoracic pain, night pain, progressive neurological deficit, cauda equina symptoms, steroid use.
• Mechanical back pain — most common; managed with simple analgesia, staying active, exercise, physiotherapy (NICE NG59 — no paracetamol alone or opioids routinely; no imaging without red flags).
• Inflammatory back pain — young, morning stiffness over 30 minutes, improves with exercise, night pain — axial spondyloarthritis.