NBME Surgery Form 3 - Answers & Explanations

Updated: Nov 16, 2019

1) Malignant hyperthermia

• Malignant hyperthermia can occur up to 12 hours after exposure to causative drug

• Fever, encephalopathy, unstable vitals, “lead pipe” muscle rigidity

2) Inhibited synthesis of prostacyclin

• Ketorolac (NSAID) inhibits the vasodilatory properties of prostacyclin → constriction of afferent arterioles → renal failure (↑ creatinine)

3) Biliary atresia

• Initially well-appearing followed by jaundice and conjugated hyperbilirubinemia over the next 1-8 weeks

• Dx: Ultrasound showing absent or abnormal gallbladder; gold standard is intra-operative cholangiogram showing biliary obstruction

• Tx: Kasai procedure (hepatoportoenterostomy) or liver transplant; Biliary atresia is the most common indication for pediatric liver transplantation

• Breast milk jaundice would present with unconjugated hyperbilirubinemia

4) Crohn disease

• “String sign” on barium x-ray = thin luminal contrast, usually in terminal ileum from spasm and eventual fibrosis

• ~50% of patients present with a palpable abdominal mass, usually in the RLQ

5) Sarcoidosis

• B/L hilar adenopathy, course reticular infiltrates, often asymptomatic

6) Bacterial overgrowth

• Decreased gastric acid/motility → bacterial overgrowth

• Tx: antibiotics (hence improvement with tetracycline)

7) CT scan of the abdomen and kidneys

• Emergent surgery is not warranted as there are no alarm signs

• Imaging should be performed to evaluate the type of management she requires

8) Insulinoma

• Whipple triad

• Increased C-peptide = endogenous source

9) Rapid administration of 500 mL of 0.9% saline

• Water challenge test - give 500 mL of normal saline, if the patient can urinate and post void volume is normal than it was dehydration. However if no urine is produced then its acute renal failure

10) Complication of right atrial catheter

• Hickman line = central venous catheter most often used for administration of chemo

• Complications of Hickman line include hemorrhage and pneumothorax during insertion.

• Complications at later stages include thrombosis and infection - the line should be regularly flushed with saline to prevent blood clots/blockage

• This patient has engorgement of veins, no arteries (arterial embolism)

11) Myocardial infarction • Cardiogenic shock: cold/clammy, tachycardia, hypotension, increased PCWP

12) C8 • No loss of reflex; Biceps C5, C6 and Triceps C6, C7 • C8 Ulnar nerve is responsible for sensation in the ring and pinky finger

13) Craniotomy • Chronic subdural hematoma → urgent surgical evacuation of symptomatic or large bleeds

14) Esophagoscopy and biopsy • Alarm sxs → must rule out cancer with endoscopic biopsy

15) Observation • Topical silver sulfadiazine therapy can be used for partial/full thickness burns

16) Carotid stenosis

• Multiple Hollenhorst plaques indicates possible embolism from carotid stenosis leading to amaurosis fugax

• Carotid duplex identifies degree of lumen narrowing

• Black rim = peripapillary atrophy, a common incidental finding that is irrelevant in this case

• Diabetic retinopathy is insidious, not acute

• Glaucoma would also be insidious with a high cup to disc ratio (this patients ratio is normal)

17) Mitral stenosis • Opening snap with late diastolic rumbling

18) Ectopic pregnancy • Cornual pregnancy = ectopic pregnancy in the interstitial portion of fallopian tube invading through the uterine wall

19) Intravenous administration of fluids • Mallory-Weiss tear with hypotension secondary to multiple bouts of bloody emesis

20) Pilonidal abscess • Common in young males at the superior gluteal cleft

21) Pulmonary contusion • Parenchymal bruising of the lung → intra-alveolar hemorrhage and edema • Commonly after blunt thoracic trauma → tachypnea, tachycardia, and hypoxia • Physical exam: ↓ breath sounds and chest wall bruising • Dx: CT shows patchy irregular alveolar infiltrate (may not show up right away on CXR)

• Tx: pain control, supplemental oxygen

22) Surgical exploration of the right femoral artery

• Comminuted fracture = break or splintering of bone into > 2 fragments

• Absent popliteal, tibial and DP pulses (which all arise from the femoral artery) - femoral artery should be explored to see where it was damaged

• In traumatic injuries, bone should be fixed first, then vascular injuries, and finally nerve injuries; reduction of bone may displace and damage vascular structures which is why is should take place first

23) Exploratory laparotomy • Although this patient only has a hematocrit of 15% and normally wouldn’t be operated on, the presence of rebound tenderness (peritonitis) and absence of bowel sounds indicated the necessity for surgery

24) Patent ductus arteriosus • Continuous machine like murmur

25) FEV1 • DLCO or FEV1 provide the best estimate of post-op morbidity

• DLCO or FEV1 < 40% → moderate/high risk of post-op morbidity

• Normal FEV1 is ~4L in males, ~3L in females

26) Renal cell carcinoma • Classic triad: painless hematuria, flank pain, abdominal mass

• PTHrP → hypercalcemia and hypophosphatemia

27) Exploratory thoracotomy • Boerhaave syndrome → surgical repair

28) Renal artery stenosis

• RAS = narrowing of renal arteries most often caused by atherosclerosis or fibromuscular dysplasia

• Smoking and angina indicate underlying atherosclerotic disease

• Fibromuscular dysplasia is more common in females

29) Thrombocytopenia • Patient only received pRBCs → dilution of platelets

• Larger transfusions require a 1:1:1 ratio of pRBCs, platelets, plasma

• In general, once you administer the 4th pRBC, a unit of platelets should be given

30) Antithrombin III deficiency • Recurrent clots in a young patient with no inciting event = hereditary thrombosis syndrome leading to hyper-coagulability

31) Splenectomy

• First-line treatment of ITP is steroids and IVIG

• Refractory ITP should be treated with splenectomy to prevent further destruction of platelets

32) Endotracheal intubation

• Rapidly expanding hematoma will quickly lead to airway compromise - intubation is quick and hence the best option

• No time to go to the OR and perform a tracheostomy

• Cricothyroidotomy can be done immediately at the bedside (but is not an answer choice for this question)

33) Administer hydrocortisone • She’s been taking prednisone - she likely has adrenal atrophy/insufficiency (body couldn’t compensate for the stress of surgery)

34) Acoustic neuroma (vestibular schwannoma) • Sensorineural hearing loss → Weber localizes to unaffected side • Can enlarge at the cerebellopontine angle leading to impingement of CN V & VII

35) Recommend a walking program • Intermittent leg claudication should be treated with smoking cessation and graded exercise program

36) Preformed antibodies to leukocyte antigens

• Febrile non-hemolytic transfusion reaction

• Two possible mechanisms: accumulation of cytokines during storage of products or type II HSR with host antibodies against donor HLA and WBCs

37) Insulin therapy

• Enzyme replacement eliminates the need for nutritional support

• Chronic pancreatitis → destruction of pancreatic islet cells → diabetes (insulin dependent)

• Secretagogues like sulfonylurea will not work as they require functioning β cells to work

38) Scarring and fibrosis of a duodenal ulcer crater

• Succession splash = gastric outlet obstruction (hollow viscus filled with fluid and gas → splash)

• Borborygmus = hyperactive loud rumbling/gurgling abdominal noises (commonly heard in SBO)

39) Ruptured bronchus • Crepitus, subcutaneous emphysema, “persistent air leak despite chest tube placement” = tracheobronchial injury

40) Pancreatic insufficiency

• Acute pancreatitis developing in chronic pancreatitis; amylase/lipase levels may be normal in chronic pancreatitis

• Insufficient enzyme production → steatosis and diabetes

• Ferritin is an acute phase reactant (elevates during inflammation)

• Lack of significant AST/ALT elevation = non-cirrhotic liver, which rules out hemochromatosis

41) Lateral x-ray

• CT is expensive and has high amounts of radiation; X-ray is a better screening tool

• MRI and CT (more sensitive imaging) can be used later on when the patient is stabilized

42) Decreases serum thyroid-stimulating (TSH) concentration and increased triiodothyronine (T3) and thyroxine (T4) concentrations • If TSH were increased it would likely enlarge the entire thyroid • Toxic adenoma = focal patch of hyper-functioning follicular cells working independently of TSH

43) Ventilatory insufficiency • Respiratory acidosis due to ventilatory insufficiency • C3-4 contributes to the phrenic nerve - block at this level → hypoventilation

44) Reassurance

• Young female with no mass and gradually resolving pain

45) Achalasia

• The esophagus is located in the posterior mediastinum; esophageal dilation → widened mediastinum

• Absent lower esophageal sphincter relaxation = Achalasia

• Air-fluid levels are present when there is a blockage/obstruction

46) Contrast enema • Currant jelly stools, drawing up of knees to relieve pain = intussusception

• Contrast enema to un-invert the intussusception

47) Pelvic ultrasonography • Work-up of ovarian mass = transvaginal U/S

• Tamoxifen has agonist effects on the bone and endometrium

48) Appendectomy

• Clinical diagnosis (no imaging required)

49) Strangulated inguinal hernia

• Fever, tachycardia, ↑ WBC count, redness of skin = signs of strangulated hernia

• Nausea/vomiting, superiorly displaced testicle, absent crematoria reflex, and testicular pain = testicular torsion

50) Ulcerative colitis • > 6 cm in transverse colon = toxic megacolon (may be initial presentation of UC) • > 12 cm in cecum, > 8 cm in ascending colon, > 6 cm in transverse colon = enlarged

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