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04 / Anatomy · Danger zones

The structures surgery is designed around

Every classic operation has one structure whose injury defines its catastrophe: the nerve, duct or vessel the whole choreography exists to protect. Learn these and you understand why operations are done the way they are, which is a deeper thing than knowing their steps.

Danger zone

Dealing the round…

The zones, one by one

  • Laparoscopic cholecystectomy

    Common bile duct

    Where you meet it
    In the hepatocystic triangle, running just medial to the cystic duct the operation intends to clip.
    Why it is at risk
    Inflammation shortens and tents the cystic duct until the common duct can masquerade as it; the classic injury is clipping and dividing the wrong duct with complete confidence.
    If it is injured
    A divided common bile duct is a life-altering injury: biliary reconstruction, lifelong stricture risk, and litigation's most famous general-surgical lesion.
    How surgeons protect it
    The Critical View of Safety: the triangle cleared until exactly two structures enter the gallbladder and the lower gallbladder is off its liver bed, before anything is clipped.
    See the operation The anatomy chapter OR Prep

  • Thyroidectomy

    Recurrent laryngeal nerve

    Where you meet it
    In the tracheo-oesophageal groove, crossing or passing near the inferior thyroid artery, millimetres deep to the gland being lifted.
    Why it is at risk
    The nerve is thread-thin, variable, and lies exactly where the gland's blood supply is ligated; traction, diathermy heat and blind clamping in a bloody field are its enemies.
    If it is injured
    Unilateral injury: a hoarse, breathy voice. Bilateral injury: both cords fall toward the midline and the airway obstructs, a post-thyroidectomy emergency.
    How surgeons protect it
    Identify the nerve before dividing anything near it, ligate branches on the capsule, keep energy devices away once seen, and check cord movement after.
    See the operation OR Prep

  • Axillary dissection

    Long thoracic nerve

    Where you meet it
    On the medial wall of the axilla, running vertically on serratus anterior behind the nodal packet being cleared.
    Why it is at risk
    It lies bare on the muscle in the exact plane of the dissection, and it looks like nothing, a pale thread against pale muscle, in a field full of lymphatic tissue.
    If it is injured
    Winged scapula: serratus anterior fails, the scapula lifts off the chest wall, and reaching forward and overhead is permanently weakened.
    How surgeons protect it
    Find it early against the chest wall, keep the dissection lateral to it, and treat every vertical thread on serratus as the nerve until proven otherwise.

  • Total hip arthroplasty (posterior approach)

    Sciatic nerve

    Where you meet it
    Emerging below piriformis, directly behind the hip joint the posterior approach opens, under the very retractors that hold the view.
    Why it is at risk
    The approach works millimetres from it: retractor blades lever near it, the hip is dislocated by rotating the leg around it, and limb lengthening stretches it.
    If it is injured
    Foot drop and a numb sole, the commonest serious nerve injury of hip surgery, sometimes permanent.
    How surgeons protect it
    Know where it runs before the first retractor, place blades on bone rather than soft tissue, limit lengthening, and check ankle dorsiflexion in recovery.
    See the operation OR Prep

  • Carotid endarterectomy

    Hypoglossal nerve

    Where you meet it
    Crossing the internal and external carotid arteries a couple of centimetres above the bifurcation, exactly where the arteriotomy's upper exposure works.
    Why it is at risk
    High plaques force the dissection up to and past it, and it hides behind a veil of small veins that bleed at the worst moment.
    If it is injured
    The tongue deviates to the injured side and speech and swallowing suffer, in a patient who consented to a stroke-prevention operation.
    How surgeons protect it
    Identify it before extending the exposure upward, sling it gently if it must move, and control the overlying veins deliberately rather than reactively.
    See the operation OR Prep

  • Open inguinal hernia repair

    Ilioinguinal nerve

    Where you meet it
    Immediately under the external oblique aponeurosis, the first structure the scissors meet on opening the canal.
    Why it is at risk
    It lies on the very cord the operation dissects and beside the mesh the operation places; entrapment by a suture or the mesh is as damaging as division.
    If it is injured
    Chronic groin pain, the commonest serious complaint after hernia repair, and numbness of the groin and scrotum or labium.
    How surgeons protect it
    Find it at the moment the canal opens, protect or deliberately handle it, and keep fixation sutures away from where it runs.
    See the operation The anatomy chapter OR Prep

  • Chest drain insertion

    Intercostal neurovascular bundle

    Where you meet it
    In the subcostal groove under each rib, hidden from the operator by the rib itself.
    Why it is at risk
    The bundle cannot be seen from outside; only technique protects it, and a drain forced under a rib rather than over one finds the artery.
    If it is injured
    Intercostal artery bleeding into the pleural space, a haemothorax caused by the treatment for one, and chronic neuralgic chest-wall pain.
    How surgeons protect it
    Always work over the top edge of the rib below the chosen space, blunt dissection, and a finger before any tube.
    See the operation OR Prep

  • Tonsillectomy

    Internal carotid artery

    Where you meet it
    A centimetre or so lateral and posterior to the tonsillar fossa, closer still in young children and in aberrant courses.
    Why it is at risk
    Deep or lateral diathermy and deep suture bites pass toward it through a wall the operator cannot see beyond.
    If it is injured
    Catastrophic haemorrhage in a shared, unprotected airway, rare, and rehearsed precisely because it is unsurvivable if unrehearsed.
    How surgeons protect it
    Depth discipline: dissect on the capsule, keep diathermy superficial and brief, and never chase bleeding blindly into the lateral wall.
    See the operation OR Prep

  • Left colectomy and Hartmann's

    Left ureter

    Where you meet it
    Crossing under the sigmoid mesocolon at the pelvic brim, in the exact plane where the mesentery is divided.
    Why it is at risk
    In inflammation or bleeding the retroperitoneal planes close up, and the ureter's peristalsis, its one identifying trick, is easy to miss in a hurried field.
    If it is injured
    A ligated or divided ureter: urinoma, sepsis, nephrostomy, and a reconstruction the patient never consented to.
    How surgeons protect it
    Find it and see it peristalse before dividing anything; if the field is hostile, find it higher where the planes are virgin and follow it down.
    See the operation OR Prep

  • Parotidectomy

    Facial nerve

    Where you meet it
    Emerging from the stylomastoid foramen and branching inside the gland itself, the tumour's neighbourhood is the nerve's home.
    Why it is at risk
    The nerve does not run past the parotid; it runs through it, so the operation is a nerve dissection with a gland attached.
    If it is injured
    Facial paralysis: a drooping face, an eye that cannot close and protect itself, and the most visible complication in head and neck surgery.
    How surgeons protect it
    Find the trunk first at its landmarks, trace the branches forward with the gland lifted off them, and use the nerve stimulator when anatomy blurs.