FCPS Part 1 Surgery and Allied Paper 2 MCQs

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.

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.

Answer: IV methylene blue

Methaemoglobinaemia: iron oxidised to Fe³⁺, which cannot carry O₂ and shifts the curve left. Causes: benzocaine, prilocaine, dapsone, nitrites, nitrates, primaquine; congenital NADH-cytochrome b5 reductase deficiency. Methylene blue (via NADPH methaemoglobin reductase) reduces it back; it is ineffective or harmful in G6PD deficiency. Hydroxocobalamin and thiosulfate treat cyanide.

Why the other options are wrong

• Hyperbaric oxygen CO poisoning.
• Hydroxocobalamin Cyanide.
• Sodium thiosulfate Cyanide.
• Exchange transfusion as first line For severe cases or G6PD deficiency.

Answer: Osteoporosis

Aromatase inhibitors (anastrozole, letrozole, exemestane) block peripheral conversion of androgens to oestrogen, the main oestrogen source after menopause. Very low oestrogen causes bone loss and arthralgia, so DEXA scanning, calcium, vitamin D and bisphosphonates where needed are advised. Tamoxifen, by contrast, protects bone but raises the risk of endometrial cancer and VTE.

Exam trap Aromatase inhibitors alone do not work in premenopausal women with functioning ovaries.

Why the other options are wrong

• Endometrial cancer Risk with tamoxifen, not aromatase inhibitors.
• Venous thromboembolism mainly Higher with tamoxifen.
• Retinal detachment Not a recognised effect.
• Hypothyroidism Not a recognised effect.

Answer: Bile supersaturated with cholesterol

Cholesterol stones form when bile holds more cholesterol than bile salts and lecithin can keep in micelles, when nucleation is promoted, and when the gallbladder empties poorly. Rapid weight loss mobilises body cholesterol into bile and reduces gallbladder motility, so supersaturated bile forms crystals and stones. Ursodeoxycholic acid can be given during rapid weight loss to prevent this. Haemolysis gives black pigment stones, and bacterial deconjugation gives brown pigment stones in infected ducts.

Exam trap More bile salts would prevent, not cause, cholesterol stones.

Why the other options are wrong

• Haemolysis increasing bilirubin load Gives black pigment stones.
• Bacterial deconjugation of bilirubin Gives brown pigment stones in infected ducts.
• Increased bile salt secretion More bile salt protects against cholesterol stones.
• Excess calcium in bile Not the main mechanism here.

Answer: Poorly controlled diabetes mellitus

Caudal regression syndrome results from defective development of caudal mesoderm early in the fourth week, leading to absent or malformed sacral and lumbar vertebrae, hypoplastic lower limbs, and anorectal and urogenital anomalies. It is strongly associated with maternal pre-gestational diabetes, because high glucose in early organogenesis disturbs mesoderm formation. Good glucose control before conception reduces this and other diabetic embryopathies.

Exam trap HbA1c before conception, not later in pregnancy, best predicts anomaly risk.

Why the other options are wrong

• Iron-deficiency anaemia Affects fetal growth, not caudal mesoderm.
• Untreated hypothyroidism Affects neurodevelopment, not the sacrum.
• Rubella in the first trimester Causes cataract, deafness and heart defects.
• Pre-eclampsia Affects the placenta late in pregnancy.

Answer: Type I slow oxidative

Type I fibres contract slowly, have many mitochondria, much myoglobin and a dense capillary supply, and rely on oxidative metabolism, so they resist fatigue. They dominate postural muscles such as soleus and are increased by endurance training. Type IIb fibres are large, pale, glycolytic and fatigue quickly, while type IIa fibres have intermediate properties. Intrafusal fibres lie inside muscle spindles.

Exam trap Fibre type is set by the motor neuron; cross-innervation experiments change it.

Why the other options are wrong

• Type IIa fast oxidative Fast and oxidative; intermediate, not small and dark red.
• Type IIb fast glycolytic Pale, large and low in myoglobin.
• Intrafusal fibres Small sensory fibres inside spindles, not the main muscle mass.
• Cardiac muscle fibres Soleus is skeletal muscle.

Answer: Nerve membranes become more permeable to sodium

Extracellular calcium normally stabilises voltage-gated sodium channels in nerve membranes. When ionised calcium falls, these channels open more easily, the threshold falls, and nerves fire spontaneously or repetitively. This hyperexcitability of motor and sensory nerves gives perioral tingling, tetany, carpopedal spasm and a positive Chvostek sign (twitching when the facial nerve is tapped). Low calcium actually reduces transmitter release, so the problem is in the nerve, not the junction.

Exam trap Alkalosis lowers ionised calcium and can cause tetany even with normal total calcium.

Why the other options are wrong

• Muscle cells release more calcium from the SR Contraction is not driven by low extracellular calcium in this way.
• Acetylcholine release at the junction rises Low calcium reduces transmitter release.
• Action potentials become longer in muscle This is not the cause of tetany.
• Nerve membranes become less permeable to potassium Potassium channels are not the main target.

Answer: 7 mmHg inwards

Net filtration pressure equals (capillary hydrostatic − interstitial hydrostatic) − (plasma oncotic − interstitial oncotic). Here that is (15 − 0) − (25 − 3) = 15 − 22 = −7 mmHg. A negative value means the net force favours reabsorption, so fluid moves 7 mmHg inwards at the venous end. Fluid filtered at the arterial end that is not reabsorbed is returned by lymph.

Exam trap Interstitial oncotic pressure pulls fluid out, so it is subtracted from plasma oncotic pressure.

Why the other options are wrong

• 7 mmHg outwards The sign is reversed.
• 13 mmHg inwards Ignores the interstitial oncotic pressure.
• 37 mmHg outwards Adds the forces instead of subtracting them.
• No net movement The forces are not balanced.

Answer: Hypotonic, with a higher potassium

This is a parotid fistula leaking saliva. Acinar cells make an isotonic, plasma-like primary secretion. As it passes along the striated ducts, Na⁺ and Cl⁻ are reabsorbed while K⁺ and HCO₃⁻ are secreted, and the ducts are fairly impermeable to water, so the final saliva is hypotonic with K⁺ above plasma levels. At high flow rates there is less time for duct modification, so saliva becomes less hypotonic, but it never becomes hypertonic.

Exam trap Saliva is the only GI secretion that is hypotonic; at high flow it becomes less so, not hypertonic.

Why the other options are wrong

• Isotonic, with a plasma-like sodium The ducts modify the isotonic primary secretion.
• Hypertonic, with a higher sodium Saliva is never hypertonic; sodium is reabsorbed.
• Hypotonic, with a lower potassium Potassium is secreted by the ducts, so it is higher.
• Isotonic, with a higher chloride Chloride is reabsorbed with sodium in the ducts.

Answer: Via the portal vein from colonic ulcers

Trophozoites invade the colonic mucosa, usually in the caecum and ascending colon, forming flask-shaped ulcers. They enter mesenteric venules and are carried in portal blood to the liver, where they lyse hepatocytes and form an abscess of liquefied, 'anchovy-sauce' material. The right lobe is affected far more often, partly because blood from the superior mesenteric vein, draining the caecum, streams mainly to it. Many patients have no history of dysentery.

Exam trap A normal stool examination does not exclude amoebic liver abscess.

Why the other options are wrong

• Via lymphatics to the cisterna chyli Amoebae do not spread by lymphatics.
• Up the common bile duct from the duodenum Ascending biliary spread causes pyogenic, not amoebic, abscesses.
• By direct spread through the colonic wall Direct spread through the wall causes perforation, not liver abscess.
• Through the hepatic artery after bacteraemia Amoebic spread is portal, not arterial.

Answer: Pilocytic astrocytoma

Pilocytic astrocytoma is the commonest glioma of childhood and typically arises in the cerebellum as a cyst with an enhancing mural nodule. Histology shows bipolar 'hair-like' cells, Rosenthal fibres and eosinophilic granular bodies. It is a low-grade (WHO grade 1) tumour that is often cured by complete excision. Haemangioblastoma can look similar on MRI but occurs mainly in adults, sometimes with von Hippel-Lindau disease, and lacks Rosenthal fibres.

Exam trap Most childhood brain tumours are infratentorial, while most adult ones are supratentorial.

Why the other options are wrong

• Medulloblastoma A solid midline (vermis) tumour of small round blue cells.
• Ependymoma Arises from the floor of the fourth ventricle; shows perivascular rosettes.
• Glioblastoma Adult cerebral hemisphere tumour with necrosis.
• Haemangioblastoma Similar cyst and nodule, but in adults, with vascular stroma.

Answer: Neurogenic tumour

Neurogenic tumours are the commonest masses of the posterior mediastinum, arising from intercostal nerves, nerve roots or the sympathetic chain in the paravertebral gutter. In adults most are benign schwannomas or neurofibromas, while in children ganglioneuroma and neuroblastoma predominate. A tumour growing out through an intervertebral foramen widens it smoothly, giving a 'dumbbell' shape with an extension into the spinal canal. Thymoma, teratoma and goitre lie in the anterior or superior compartments.

Exam trap A dumbbell tumour needs spinal MRI before removal to avoid cord injury.

Why the other options are wrong

• Thymoma An anterior mediastinal mass.
• Mature teratoma An anterior mediastinal germ cell tumour.
• Bronchogenic cyst Usually lies in the middle mediastinum near the carina.
• Retrosternal goitre Lies in the superior and anterior mediastinum.