During a total thyroidectomy, the surgeon ligates the inferior thyroid artery close to the gland. After surgery the patient's voice is hoarse and weak. Which nerve has most likely been injured?
Answer: Recurrent laryngeal nerve
The recurrent laryngeal nerve runs in the tracheo-oesophageal groove and crosses the inferior thyroid artery near the lower pole. It supplies all intrinsic laryngeal muscles except cricothyroid, so injury paralyses the vocal cord on that side, causing hoarseness. Bilateral injury can cause stridor and airway obstruction.
Ligate the superior artery close to the gland; the inferior artery away from the gland
Remember Superior = Singer's nerve (pitch). Inferior = the one that makes you Rasp.
Exam trap Many question books swap them. Upper pole = external laryngeal (pitch). Lower pole / inferior thyroid artery = recurrent laryngeal (hoarseness).
Why the other options are wrong
External laryngeal nerve Runs with the superior thyroid artery at the upper pole; injury causes a weak, monotonous voice and loss of high pitch (cricothyroid), not classic hoarseness.
Internal laryngeal nerve Sensory to the larynx above the cords; injury causes loss of the cough reflex and aspiration, not hoarseness.
Ansa cervicalis Supplies infrahyoid strap muscles; cutting it does not affect the voice.
Hypoglossal nerve Supplies tongue muscles; injury causes deviation of the tongue.
Question 2Medium
A man with pancreas divisum and recurrent pancreatitis is booked for endoscopic sphincterotomy. Which of the following must the endoscopist cannulate to drain most of the gland?
Answer: Minor duodenal papilla
In pancreas divisum the ventral and dorsal pancreatic ducts fail to fuse. The dorsal duct (duct of Santorini), which drains the tail, body and most of the head, then empties through the small minor duodenal papilla, about 2 cm above and slightly in front of the major papilla. The narrow minor papilla can cause relative outflow obstruction and pancreatitis, so minor papilla sphincterotomy or stenting is the endoscopic treatment. The major papilla drains only the bile duct and the small ventral duct.
Pancreas divisum
Ducts fail to fuse
Dorsal duct drains most of gland
Opens at minor papilla
Treat by minor papilla sphincterotomy
Remember Divisum drains through the small door.
Exam trap In divisum, cannulating the major papilla shows only a short ventral duct.
Why the other options are wrong
Major duodenal papilla Drains only the bile duct and small ventral duct here.
Duodenojejunal flexure No duct opens here.
Pylorus No duct opens here.
Ampulla of the bile duct only Drains bile, not most of the pancreas.
Question 3Medium
In a fracture of the mandibular angle, the posterior fragment is pulled upwards and medially. The muscles mainly responsible are:
Answer: Masseter and medial pterygoid
The ramus is enclosed by the pterygomasseteric sling, formed by the masseter laterally and the medial pterygoid medially, both inserting near the angle. After a fracture at the angle, these muscles, helped by temporalis, pull the posterior fragment upwards and medially. Whether the fragment displaces depends on the direction of the fracture line, which decides if the muscle pull holds it together (favourable) or apart (unfavourable).
Angle fracture
Pterygomasseteric sling at the angle
Posterior fragment pulled up and medially
Anterior fragment pulled down by suprahyoids
Remember Elevators lift the back fragment; depressors drop the front.
Exam trap Condylar neck fragments are pulled forward and medially by the lateral pterygoid instead.
Why the other options are wrong
Digastric and geniohyoid Depress the anterior fragment, not the posterior one.
Mylohyoid and hyoglossus Act on the floor of mouth and tongue.
Buccinator and platysma Facial muscles; too weak to displace bone.
Lateral pterygoid and genioglossus Lateral pterygoid acts on the condyle; genioglossus on the tongue.
Question 4Easy
On cold exposure, a man's scrotal skin becomes wrinkled and tight. Which muscle produces this?
Answer: Dartos muscle
The dartos is a layer of smooth muscle in the superficial fascia of the scrotum, supplied by sympathetic fibres. In the cold it contracts, wrinkling the skin and reducing the surface area for heat loss, which helps keep testicular temperature steady. The cremaster is skeletal muscle derived from internal oblique; it lifts the testis (cremasteric reflex) and is supplied by the genital branch of the genitofemoral nerve. Bulbospongiosus and ischiocavernosus are perineal muscles.
Before a lumbar puncture for suspected meningitis, the patient lies on his side with knees drawn to his chest. Why is this position used?
Answer: Flexion opens gaps between lumbar laminae
Lumbar spinous processes and laminae overlap little, but in extension the gaps between them narrow. Full flexion of the lumbar spine separates the spinous processes and opens the interlaminar spaces, so the needle can pass in the midline between L3–L4 or L4–L5 to reach the subarachnoid space. Lying on the side also allows an accurate opening pressure to be measured. The position does not change the safety concerns about raised intracranial pressure, which must be assessed beforehand.
Lumbar puncture
Flexion opens interlaminar gaps
Needle at L3–L4 or L4–L5
Below the conus (L1–L2)
Lateral position: opening pressure
Remember Curl up to open the gaps.
Exam trap Image the brain first if there are focal signs, papilloedema or reduced consciousness.
Why the other options are wrong
It lowers CSF pressure to prevent coning Position does not prevent coning; check for raised ICP first.
It slackens the ligamentum flavum Flexion stretches, not slackens, the ligamentum flavum.
It moves the cauda equina to one side The rootlets float freely and are pushed aside by the needle anyway.
It raises the cord above the L1 level The cord ends at L1–L2; flexion does not make LP safe above that.
Question 6Medium
An MRI of the posterior pelvic wall shows the sacral plexus lying on a muscle that arises from the front of the middle sacral segments and leaves the pelvis through the greater sciatic foramen. Which muscle is this?
Answer: Piriformis
Piriformis arises from the anterior surface of S2–S4 and passes out through the greater sciatic foramen to the greater trochanter. It forms much of the posterolateral wall of the true pelvis, with the sacral plexus lying on its pelvic surface. It divides the greater sciatic foramen into suprapiriform and infrapiriform parts, which transmit the gluteal vessels and nerves.
Piriformis
From S2–S4 anteriorly
Exits greater sciatic foramen
Sacral plexus lies on it
Divides foramen above and below
Remember Piriformis is the key to the greater sciatic foramen.
Exam trap The sacral plexus lies on piriformis, so a large pelvic mass can compress it.
Why the other options are wrong
Coccygeus Arises from the ischial spine and stays in the pelvis.
Obturator internus Leaves through the lesser sciatic foramen.
Iliacus Lines the iliac fossa of the false pelvis.
Psoas major Lies on the lumbar spine above the brim.
Question 7Medium
A 26-year-old woman at 30 weeks has appendicitis. Her maximal tenderness is in the right flank, well above McBurney's point. What is the reason for this?
Answer: The enlarging uterus pushes the caecum upward
As the uterus grows into the abdomen, it pushes the caecum and appendix upward and laterally, so in the third trimester the appendix often lies near the right flank or even below the liver. The site of pain and tenderness moves with it, making diagnosis harder. The large uterus also keeps the inflamed appendix away from the parietal peritoneum of the anterior abdominal wall, so guarding may be less marked.
Appendicitis in pregnancy
Uterus displaces caecum
Appendix moves up and out
Pain in the right flank
Less guarding
Remember In late pregnancy the appendix is higher.
Exam trap Appendicitis in late pregnancy may mimic pyelonephritis or cholecystitis.
Why the other options are wrong
The appendix lengthens in pregnancy The appendix does not lengthen.
Progesterone shifts referred pain upward Hormones do not alter the site of somatic pain.
The uterus compresses the femoral nerve The femoral nerve is not involved.
The right ureter displaces the appendix The ureter does not displace the appendix.
Question 8Medium
A testicular biopsy from an infertile man shows normal spermatogonia, spermatocytes and round spermatids, but no elongated spermatids or spermatozoa. Which process has failed?
Answer: Spermiogenesis
Spermiogenesis is the transformation of round spermatids into spermatozoa, without any cell division. During it the nucleus condenses and elongates, the Golgi forms the acrosome, the centriole forms the flagellum, mitochondria gather in the middle piece and excess cytoplasm is shed as residual bodies. Round spermatids have already completed meiosis II, so arrest at this point is a failure of spermiogenesis. Spermiation is the later release of mature sperm into the lumen.
Spermiogenesis
Round spermatid to spermatozoon
No cell division
Acrosome from Golgi, tail from centriole
Excess cytoplasm shed as residual body
Remember Spermiogenesis shapes; it does not divide.
Exam trap Spermatogenesis is the whole sequence; spermiogenesis is only its last, shaping stage.
Why the other options are wrong
Spermiation Release of formed sperm into the lumen; comes after.
Meiosis II Already complete, since round spermatids are present.
Capacitation Occurs in the female tract after ejaculation.
Spermatocytogenesis Mitotic and meiotic stages; these are intact.
Question 9Medium
A 45-year-old woman with metastatic breast cancer has headaches and new cranial nerve palsies, and CSF cytology shows malignant cells. Tumour coats the surface of the brain, following it deep into the sulci and over the basal cisterns. Which meningeal layer is involved?
Answer: Pia-arachnoid (leptomeninges)
The pia mater adheres to the brain surface and dips into every sulcus, and the arachnoid with the subarachnoid space follows it over the cisterns. Tumour cells carried in the CSF settle on this pia-arachnoid (leptomeninges), so they coat the gyri, sulci and cisterns, as in carcinomatous meningitis. Cranial nerve palsies arise as tumour cells coat nerves in the basal cisterns. The dura lines the inner table and does not enter sulci.
Leptomeninges
Pia follows every sulcus
Arachnoid covers the cisterns
CSF spread coats the leptomeninges
Cranial nerve palsies from basal cistern deposits
Remember Disease dipping into sulci is leptomeningeal.
Exam trap CSF cytology may need repeated samples; a normal first result does not exclude carcinomatosis.
Why the other options are wrong
Dura mater (pachymeninges) Lines the inner table without dipping into sulci.
Periosteal layer of the skull Lies outside the dura and does not reach the sulci.
Ependymal lining of the ventricles Lines the ventricles, not the brain surface.
Choroid plexus epithelium Lies within the ventricles.
Question 10Easy
At cholecystectomy in an asymptomatic woman, the gallbladder fundus is found folded back on the body, with a kink like a septum but a normal wall and no stones. What is this normal variant called?
Answer: Phrygian cap
A Phrygian cap is a common normal variant in which the fundus folds over the body, producing a septum-like kink. It causes no symptoms and does not need treatment. It should not be mistaken for a mass, septum of a duplication or adenomyomatosis.
Phrygian cap
Fundus folded over the body
Normal variant
No symptoms or treatment
Remember A folded fundus is a cap, not a disease.
Exam trap Do not mistake the fold for a septum, stone or mass.
Why the other options are wrong
Gallbladder duplication Two separate lumens with two cystic ducts.
Hartmann pouch A pouch at the neck, not the fundus.
Adenomyomatosis Wall thickening with comet-tail artefacts.
Gallbladder polyp A small fixed projection into the lumen.
Question 11Easy
For radial artery cannulation at the wrist, between which two tendons does the radial artery lie?
Answer: Brachioradialis and flexor carpi radialis
At the wrist the radial artery lies superficially on the distal radius and pronator quadratus, just lateral to the tendon of flexor carpi radialis and medial to the tendon of brachioradialis. Here it can be felt against bone for the pulse and is easily punctured. The median nerve lies deeper and between flexor carpi radialis and palmaris longus. The ulnar artery and nerve lie lateral to flexor carpi ulnaris.
Radial artery at the wrist
Lateral to flexor carpi radialis
Medial to brachioradialis tendon
On the distal radius (easy pulse)
Median nerve between FCR and palmaris longus
Remember Radial pulse: just lateral to FCR.
Exam trap The superficial branch of the radial nerve lies close by; repeated punctures can injure it.
Why the other options are wrong
Flexor carpi radialis and palmaris longus The median nerve lies near this gap, not the radial artery.
Palmaris longus and flexor carpi ulnaris The ulnar artery is near flexor carpi ulnaris, on the medial side.
Abductor pollicis longus and brachioradialis APL lies more laterally, around the radial styloid.
Flexor pollicis longus and flexor carpi ulnaris Too far apart; this is not where the artery lies.
Question 12Medium
A 6-week-old baby has fever and keeps her left leg still and flexed. She has osteomyelitis of the proximal femoral metaphysis that has spread into the hip joint. Why does metaphyseal osteomyelitis at this site so often lead to septic arthritis?
Answer: The metaphysis lies inside the hip joint capsule
At the hip, the joint capsule attaches to the femoral neck below the physis, so the proximal femoral metaphysis lies within the joint. Pus that breaks through the thin metaphyseal cortex therefore enters the joint directly. In infants under about 18 months, vessels also cross the physis into the epiphysis, providing another route. The same is true at the shoulder, elbow and ankle. Septic arthritis of the hip in infants threatens the femoral head blood supply and needs urgent drainage.
Remember An intracapsular metaphysis lets pus into the joint.
Exam trap Infants with septic hip may have little fever and few signs, so a leg held still needs urgent assessment.
Why the other options are wrong
The femoral head has no blood supply in infants The femoral head has a blood supply; infection threatens it, but that is not why spread occurs.
The joint capsule is absent in infants The capsule is present and attaches below the physis on the femoral neck.
Bacteria spread through the ligamentum teres The ligamentum teres artery is small and is not the main route of spread.
The periosteum is firmly bound to the cortex In children the periosteum is loosely attached, which allows subperiosteal abscesses rather than preventing spread.
