Question 1: Colorectal Carcinoma (CRC)
Stem: A 70-year-old man presents with iron-deficiency anaemia and a change in bowel habits. A CT colonography is performed, which reveals a 4 cm, focal, circumferential mass in the sigmoid colon. The mass causes an abrupt, “shouldered” narrowing of the lumen, with an “overhanging edge.”
Question: This radiographic appearance is known as the:
(A) “Apple Core Sign” (B) “Kantor String Sign” (C) “Bird’s Beak Sign” (D) “Lead Pipe Sign” (E) “Comb Sign”
Correct Answer: (A) “Apple Core Sign”.
Explanation:
- Why (A) is correct: The “apple core sign” is the classic description of an annular, constricting adenocarcinoma of the colon. The “shouldered” margins and abrupt, short-segment narrowing resemble a partially eaten apple core.
- Why (B) is wrong: The “Kantor string sign” is a long, thin segment of narrowing seen in Crohn’s disease.
- Why (C) is wrong: The “bird’s beak sign” is the smooth, tapered narrowing of the oesophagus in achalasia.
- Why (D) is wrong: The “lead pipe sign” is the loss of haustra in chronic ulcerative colitis, making the colon appear as a featureless, rigid tube.
- Why (E) is wrong: The “comb sign” is a CT finding of active Crohn’s disease (engorged vasa recta).
Key Points: Colorectal Carcinoma (CRC)
- Definition: Most common malignancy of the GI tract; 98% are adenocarcinomas.
- Imaging (Barium or CT):
- “Apple Core Sign”: A short, annular, constricting lesion with “shouldered” edges.
- Can also be a polypoid, exophytic mass.
- Location: Most common in the rectosigmoid region.
- Staging: CT chest/abdomen/pelvis is the primary staging modality (TNM staging). Look for wall invasion, lymph nodes, and liver/lung metastases.
Question 2: Ulcerative Colitis (UC)
Stem: A 30-year-old woman with a 10-year history of bloody diarrhoea undergoes a barium enema. The study shows continuous, circumferential, and symmetric involvement of the entire colon, starting from the rectum. The bowel wall is featureless, with a complete loss of the normal haustral markings.
Question: The “featureless” appearance of the colon described here is known as the:
(A) “Lead Pipe Sign” (B) “String Sign” (C) “Cobblestone Sign” (D) “Apple Core Sign” (E) “Comb Sign”
Correct Answer: (A) “Lead Pipe Sign”.
Explanation:
- Why (A) is correct: The “lead pipe” or “featureless” colon is the classic finding of chronic ulcerative colitis. The chronic, full-thickness inflammation destroys the haustra (the normal sacculations of the colon) and causes the colon to become rigid, shortened, and smooth.
- Why (B) is wrong: The “string sign” is a severe, focal narrowing in Crohn’s disease.
- Why (C) is wrong: “Cobblestoning” (from intersecting ulcers) is characteristic of Crohn’s disease, not UC.
- Why (D) is wrong: The “apple core sign” is classic for colon cancer.
- Why (E) is wrong: The “comb sign” is a CT finding in Crohn’s disease.
Key Points: Ulcerative Colitis (UC)
- Definition: An inflammatory bowel disease (IBD) confined to the mucosa and submucosa of the colon.
- Distribution:
- Always involves the rectum.
- Spreads proximally in a continuous and symmetric fashion.
- Never involves the small bowel (except for “backwash ileitis”).
- Imaging:
- Early: Fine, granular mucosa (“stippled” appearance).
- Chronic: “Lead pipe” colon (loss of haustra), colonic shortening.
- Complication: High risk of toxic megacolon and colorectal carcinoma.
Question 3: Crohn’s Disease vs. Ulcerative Colitis
Stem: A 25-year-old man presents with chronic diarrhoea, weight loss, and anal fistulae. An MR enterogram is performed.
Question: Which of the following imaging features would be most specific for a diagnosis of Crohn’s Disease rather than Ulcerative Colitis?
(A) Continuous involvement starting from the rectum. (B) Superficial mucosal inflammation only. (C) Loss of haustral markings (“lead pipe” colon). (D) Transmural inflammation with deep, “rose-thorn” ulcers and “skip lesions”. (E) An increased risk of toxic megacolon.
Correct Answer: (D) Transmural inflammation with deep, “rose-thorn” ulcers and “skip lesions”.
Explanation:
- Why (D) is correct: These are the hallmarks of Crohn’s. It is a transmural (full-thickness) inflammation, which leads to deep, penetrating ulcers (“rose-thorn”) and complications like fistulae and abscesses. It also classically involves the bowel in a discontinuous fashion, with “skip lesions” (diseased segments separated by normal bowel).
- Why (A) is wrong: Continuous rectal involvement is the hallmark of Ulcerative Colitis.
- Why (B) is wrong: Superficial (mucosal) inflammation is the hallmark of Ulcerative Colitis.
- Why (C) is wrong: The “lead pipe” colon is a finding in Ulcerative Colitis.
- Why (E) is wrong: Toxic megacolon can occur in both, but it is more famously associated with Ulcerative Colitis.
Key Points: Crohn’s vs. Ulcerative Colitis
- Crohn’s Disease:
- Location: Anywhere from mouth to anus (terminal ileum most common).
- Distribution: Skip lesions (asymmetric, discontinuous).
- Depth: Transmural (full-thickness).
- Signs: Deep ulcers (“rose-thorn”), cobblestoning, fistulae, abscesses, “comb sign” (CT), “string sign” (barium).
- Ulcerative Colitis (UC):
- Location: Colon only (always involves rectum).
- Distribution: Continuous and symmetric.
- Depth: Mucosal (superficial).
- Signs: Superficial ulcers, “lead pipe” colon.
Question 4: Toxic Megacolon
Stem: A 30-year-old woman with a known 5-year history of ulcerative colitis presents to the ED with a high fever, tachycardia, hypotension, and a severely distended, tender abdomen. A supine abdominal X-ray shows marked, contiguous dilatation of the transverse colon, which measures 9 cm in diameter. The bowel wall appears thinned and “thumbprinting” is visible.
Question: What is this life-threatening complication?
(A) Toxic Megacolon (B) Sigmoid Volvulus (C) Caecal Volvulus (D) Small Bowel Obstruction (E) Pseudomembranous Colitis
Correct Answer: (A) Toxic Megacolon.
Explanation:
- Why (A) is correct: This is the classic presentation. Toxic megacolon is an acute, non-obstructive, fulminant colitis with colonic dilatation (typically > 6 cm) and systemic toxicity (fever, tachycardia, shock). It is a life-threatening complication of Ulcerative Colitis (or, less commonly, Crohn’s or C. difficile).
- Why (B) is wrong: A sigmoid volvulus is a mechanical twist, which would show an “inverted U” or “coffee bean” sign, but not signs of systemic toxicity.
- Why (C) is wrong: A caecal volvulus is a twist of the caecum, which would appear as a dilated loop in the left upper quadrant.
- Why (D) is wrong: This is a colonic process, not small bowel.
- Why (E) is wrong: Pseudomembranous colitis can cause toxic megacolon, but “toxic megacolon” is the specific diagnosis for the finding of colonic dilatation plus toxicity.
Key Points: Toxic Megacolon
- Definition: A life-threatening, non-obstructive, fulminant colitis with colonic dilatation and systemic toxicity.
- Most Common Cause: Ulcerative Colitis.
- Radiographic Sign: Dilatation of the transverse colon > 6 cm.
- Other Signs: “Thumbprinting” (submucosal oedema), loss of haustra.
- Risk: High risk of perforation.
Question 5: Sigmoid Volvulus
Stem: An 80-year-old nursing home resident with chronic constipation presents with acute abdominal distension and obstipation. A plain abdominal radiograph shows a massively dilated, featureless (ahaustral) loop of bowel arising from the pelvis and extending into the left upper quadrant, resembling an “inverted U” or a “coffee bean”.
Question: What is the most likely diagnosis?
(A) Sigmoid Volvulus (B) Caecal Volvulus (C) Toxic Megacolon (D) Large Bowel Obstruction from a tumour (E) Ileosigmoid Knot
Correct Answer: (A) Sigmoid Volvulus.
Explanation:
- Why (A) is correct: This is the classic description. A sigmoid volvulus is a twist of a redundant sigmoid colon on its mesentery. This creates a “closed-loop” obstruction, which appears as a huge, dilated, “inverted U” (or “coffee bean”) with its apex pointing to the left upper quadrant. It is common in elderly, debilitated patients.
- Why (B) is wrong: A caecal volvulus is a twist of the caecum, which is a right-sided structure. It typically flips and appears as a dilated loop in the left upper quadrant, but it retains its haustral markings.
- Why (C) is wrong: Toxic megacolon is a non-obstructive dilatation (usually of the transverse colon) and is associated with systemic sepsis.
- Why (D) is wrong: An obstructing tumour would show dilated proximal colon, but not a single, massive, twisted loop.
- Why (E) is wrong: This is a rare, complex knot involving both the ileum and sigmoid.
Key Points: Sigmoid Volvulus
- Definition: A “closed-loop” obstruction from a twist of the sigmoid colon.
- Demographic: Elderly, constipated, institutionalised patients.
- X-ray Signs:
- “Coffee Bean Sign” or “Inverted U Sign”.
- Massively dilated, ahaustral loop.
- Apex points to the left upper quadrant.
- Treatment: Can often be decompressed with a flatus tube (sigmoidoscopy), followed by surgical fixation.
Question 6: Caecal Volvulus
Stem: A 40-year-old woman presents with acute, colicky abdominal pain. An abdominal radiograph shows a large, dilated loop of bowel that has its apex in the left upper quadrant, but the loop contains visible haustral markings. The distal colon is collapsed, and the small bowel is dilated.
Question: What is the most likely diagnosis?
(A) Sigmoid Volvulus (B) Caecal Volvulus (C) Transverse Colon Volvulus (D) Large Bowel Obstruction from a tumour (E) Gastric Volvulus
Correct Answer: (B) Caecal Volvulus.
Explanation:
- Why (B) is correct: This is the classic description of a caecal volvulus (or caecal bascule). It is a twist of the caecum (a right-sided structure) which, due to its long mesentery, “flips” into the left upper quadrant. The key differentiating feature from a sigmoid volvulus is that the caecum retains its haustral markings.
- Why (A) is wrong: A sigmoid volvulus is ahaustral (featureless).
- Why (C) is wrong: A transverse colon volvulus is very rare.
- Why (D) is wrong: This would not produce a single, displaced, twisted loop.
- Why (E) is wrong: Gastric volvulus is in the stomach.
Key Points: Caecal vs. Sigmoid Volvulus
- Sigmoid Volvulus:
- Appearance: “Coffee bean.”
- Haustra: Absent.
- Location: Rises from pelvis, apex in LUQ.
- Patient: Elderly.
- Caecal Volvulus:
- Appearance: “Kidney bean” or comma-shaped.
- Haustra: Present.
- Location: Displaced from RLQ to LUQ.
- Patient: Younger (30-50).
Question 7: Diverticulitis (Acute)
Stem: A 65-year-old man presents with a 3-day history of left iliac fossa pain, fever, and a raised white cell count. A contrast-enhanced CT of the abdomen reveals multiple, small, air-filled outpouchings (diverticula) in the sigmoid colon. There is focal, segmental wall thickening of the sigmoid, with inflammatory stranding in the adjacent pericolic fat.
Question: What is the most likely diagnosis?
(A) Acute Diverticulitis (B) Colorectal Carcinoma (C) Ulcerative Colitis (D) Crohn’s Disease (E) Epiploic Appendagitis
Correct Answer: (A) Acute Diverticulitis.
Explanation:
- Why (A) is correct: This is the classic CT triad for uncomplicated acute diverticulitis: 1) The presence of diverticula, 2) Segmental colonic wall thickening, and 3) Inflammatory stranding of the pericolic fat. The sigmoid colon is the most common site.
- Why (B) is wrong: Colon carcinoma is an infiltrative mass that causes abrupt, shouldered narrowing. It does not typically have pericolic fat stranding unless it has perforated.
- Why (C) is wrong: UC is a continuous mucosal process starting in the rectum, not a focal, segmental process related to diverticula.
- Why (D) is wrong: Crohn’s disease is a transmural process but is not caused by diverticula and often involves the terminal ileum.
- Why (E) is wrong: Epiploic appendagitis is inflammation of a fatty appendage on the colon, which appears as an ovoid, fatty mass with a “central dot,” but the colon wall itself is normal.
Key Points: Acute Diverticulitis (CT)
- Definition: Inflammation/infection of a colonic diverticulum (an outpouching of the mucosa).
- Location: Most common in the sigmoid colon.
- CT Triad (Uncomplicated):
- Diverticula.
- Segmental Wall Thickening.
- Pericolic Fat Stranding (inflammation).
- Complications (Hinchey Classification): Look for abscess, distant gas (perforation), or fistula.
Question 8: Epiploic Appendagitis
Stem: A 40-year-old man presents with acute, focal, non-migratory left-sided abdominal pain. His inflammatory markers are normal. A CT scan demonstrates a 2 cm, ovoid, fat-density lesion on the anti-mesenteric border of the sigmoid colon. This lesion is surrounded by a thin, hyperdense rim and has marked, adjacent inflammatory fat stranding. The sigmoid colon wall itself is normal.
Question: What is the most likely diagnosis?
(A) Epiploic Appendagitis (B) Acute Diverticulitis (C) Omental Infarction (D) Sigmoid Carcinoma (E) Mesenteric Panniculitis
Correct Answer: (A) Epiploic Appendagitis.
Explanation:
- Why (A) is correct: This is the pathognomonic appearance. Epiploic appendagitis is a benign, self-limiting inflammation (from torsion or thrombosis) of an epiploic appendage (a fatty tag on the colon’s surface). The CT shows an ovoid fatty lesion with a hyperdense rim (the inflamed visceral peritoneum) and surrounding inflammation. Crucially, the colon wall is normal.
- Why (B) is wrong: Diverticulitis involves inflammation of the colon wall, which would be thickened.
- Why (C) is wrong: Omental infarction is a similar process (fat inflammation) but involves the greater omentum, which is a much larger, “cake-like” structure, not a small, ovoid lesion on the colon.
- Why (D) is wrong: This is a solid, enhancing mass of the colon wall.
- Why (E) is wrong: Mesenteric panniculitis is a diffuse inflammation of the mesenteric root, not a focal lesion.
Key Points: Epiploic Appendagitis
- Definition: A benign, self-limiting inflammation (torsion/thrombosis) of an epiploic appendage.
- Clinical: Acute, focal pain; often mimics diverticulitis but without fever or leukocytosis.
- CT Hallmarks:
- Ovoid, fat-density lesion (< 5 cm) on the anti-mesenteric border of the colon.
- A hyperdense rim (“ring sign”).
- Focal, intense inflammatory fat stranding.
- Normal adjacent colon wall (key differentiator from diverticulitis).
Question 9: Pseudomembranous Colitis
Stem: A 75-year-old hospital inpatient, recently treated with clindamycin for pneumonia, develops profuse, watery diarrhoea. A CT scan of the abdomen shows diffuse, massive, circumferential thickening of the entire colon wall. The wall has a low-density (oedematous) submucosal layer, giving it a “target sign.” There is marked, shaggy enhancement of the mucosa.
Question: Given the patient’s history and the “accordion sign” appearance, what is the most likely diagnosis?
(A) Pseudomembranous Colitis (C. difficile) (B) Ulcerative Colitis (C) Cytomegalovirus (CMV) Colitis (D) Ischaemic Colitis (E) Crohn’s Disease
Correct Answer: (A) Pseudomembranous Colitis (C. difficile).
Explanation:
- Why (A) is correct: The history of recent antibiotic use is the key. This allows overgrowth of Clostridium difficile, which causes pseudomembranous colitis. The imaging findings of diffuse, pancolonic, “pancake-like” wall thickening from marked submucosal oedema are classic. The “accordion sign” (oral contrast trapped between the thick haustral folds) is highly specific.
- Why (B) is wrong: A first presentation of UC would not be this fulminant, and it is not associated with antibiotic use.
- Why (C) is wrong: CMV colitis also causes wall thickening but is seen in severely immunocompromised patients (e.g., AIDS, transplant).
- Why (D) is wrong: Ischaemic colitis is a segmental disease (classically the “watershed” sigmoid or splenic flexure) and presents with a lack of enhancement; this is a diffuse, enhancing process.
- Why (E) is wrong: Crohn’s disease is a focal, “skip-lesion” disease.
Key Points: Pseudomembranous Colitis
- Cause: Toxin from Clostridium difficile overgrowth.
- Risk Factor: Recent antibiotic use.
- CT Findings:
- Pancolonic (or diffuse) wall thickening.
- Massive submucosal oedema (low-density wall).
- “Accordion Sign”: Oral contrast trapped in oedematous folds.
- “Target Sign”: Layered enhancement.
- Complication: Can progress to toxic megacolon and perforation.
Question 10: Ischaemic Colitis
Stem: An 80-year-old man with severe peripheral vascular disease and atrial fibrillation presents with acute-onset, bloody diarrhoea and left-sided abdominal pain. A CT scan shows segmental, circumferential wall thickening of the colon, specifically at the splenic flexure. This segment appears oedematous and has a “target sign” appearance.
Question: This location is a classic “watershed” area, making which diagnosis most likely?
(A) Ischaemic Colitis (B) Crohn’s Disease (C) Ulcerative Colitis (D) Diverticulitis (E) Pseudomembranous Colitis
Correct Answer: (A) Ischaemic Colitis.
Explanation:
- Why (A) is correct: The splenic flexure is a classic “watershed area”. It is the boundary between the blood supply of the Superior Mesenteric Artery (SMA) and the Inferior Mesenteric Artery (IMA). In low-flow states (e.g., hypotension, or in this patient, likely non-occlusive disease from PVD/AFib), this area is the most vulnerable to ischaemia. The segmental wall thickening is the result of oedema and haemorrhage.
- Why (B) is wrong: Crohn’s disease is rare in the splenic flexure and more common in the terminal ileum.
- Why (C) is wrong: UC starts in the rectum and is continuous; it would not present as an isolated, segmental lesion at the splenic flexure.
- Why (D) is wrong: Diverticulitis is most common in the sigmoid colon.
- Why (E) is wrong: This is a diffuse, pancolonic process.
Key Points: Ischaemic Colitis
- Definition: The most common form of bowel ischaemia, typically non-occlusive (low-flow state).
- Classic “Watershed” Locations:
- Splenic Flexure (Griffiths’ point): SMA-IMA boundary.
- Rectosigmoid Junction (Sudeck’s point): IMA-Iliac boundary.
- CT Findings:
- Segmental wall thickening (oedema, “thumbprinting”).
- “Target sign” (layered enhancement).
- Can progress to pneumatosis and perforation.
Question 11: Appendicitis
Stem: A 20-year-old man presents with a 24-hour history of periumbilical pain that has now migrated to the right iliac fossa (RIF). He is febrile and has a raised white cell count. A CT scan is performed.
Question: Which of the following is the most specific CT finding for acute appendicitis?
(A) A fluid-filled caecum. (B) Multiple, enlarged, reactive iliac lymph nodes. (C) A dilated (> 6 mm), fluid-filled appendix with a thickened, enhancing wall and periappendiceal fat stranding. (D) A normal-appearing appendix (< 6 mm) with an adjacent fluid collection. (E) A focal, ovoid, fatty lesion with a hyperdense rim.
Correct Answer: (C) A dilated (> 6 mm), fluid-filled appendix with a thickened, enhancing wall and periappendiceal fat stranding.
Explanation:
- Why (C) is correct: This is the complete CT description of acute appendicitis. The key diagnostic findings are: 1) Appendiceal diameter > 6 mm, 2) A fluid-filled, non-opacified lumen, 3_ Wall thickening/hyperenhancement, and 4) Periappendiceal fat stranding (inflammation).
- Why (A) is wrong: This is a non-specific finding.
- Why (B) is wrong: This is reactive adenopathy, a consequence of the inflammation, not the primary cause.
- Why (D) is wrong: This would suggest a perforated appendicitis where the appendix has decompressed, or inflammation near the appendix (e.g., diverticulitis). A normal-appearing appendix makes appendicitis unlikely.
- Why (E) is wrong: This is the classic description of epiploic appendagitis.
Key Points: Acute Appendicitis
- Definition: Inflammation of the vermiform appendix, usually from obstruction (e.g., faecolith).
- CT Findings (Primary):
- Dilated appendix (> 6 mm outer-to-outer diameter).
- Wall thickening and hyperenhancement.
- Periappendiceal fat stranding.
- CT Findings (Secondary/Complications):
- Appendicolith: A calcified faecolith (a strong predictor).
- Abscess: A contained, enhancing fluid collection.
- Perforation: Focal wall defect, free fluid, or extraluminal gas.
Question 12: Pseudomyxoma Peritonei (PMP)
Stem: A 60-year-old man presents with a 6-month history of increasing abdominal girth, giving him a “jelly belly” appearance. A CT scan of the abdomen shows a massive volume of low-attenuation (near-fluid) ascites that is not free-flowing, but is loculated. It is causing mass effect on the solid organs, with characteristic scalloping of the surface of the liver and spleen.
Question: This combination of mucinous ascites and visceral scalloping is pathognomonic for:
(A) Pseudomyxoma Peritonei (PMP) (B) Tuberculous Peritonitis (C) Cirrhosis with Ascites (D) Peritoneal Carcinomatosis (E) Omental Infarction
Correct Answer: (A) Pseudomyxoma Peritonei (PMP).
Explanation:
- Why (A) is correct: PMP is a rare malignancy (low-grade appendiceal mucinous neoplasm is the classic primary) that fills the peritoneum with mucinous ascites. This “jelly-like” material is thick, loculated, and causes a characteristic mass effect on the solid organs, leading to scalloping of the visceral surfaces (especially the liver).
- Why (B) is wrong: TB peritonitis causes high-density ascites and enhancing peritoneal nodules, not mucinous ascites with scalloping.
- Why (C) is wrong: Cirrhotic ascites is simple, free-flowing fluid (not loculated) and does not cause scalloping (the liver is shrunken and nodular on its own).
- Why (D) is wrong: Carcinomatosis (e.g., from ovarian cancer) causes nodular peritoneal thickening (“omental cake”) and high-density ascites, not the scalloping effect of mucin.
- Why (E) is wrong: This is a focal, inflammatory fat process.
Key Points: Pseudomyxoma Peritonei (PMP)
- Definition: A rare “jelly-belly” malignancy.
- Primary Source: Almost always a ruptured low-grade mucinous neoplasm (LAMN) of the appendix.
- CT Hallmarks:
- Large-volume, loculated, low-attenuation (mucinous) ascites.
- Scalloping of the visceral surfaces (especially the liver and spleen).
- Can have curvilinear calcifications.
Question 13: Peritoneal Carcinomatosis
Stem: A 65-year-old woman with a history of ovarian cancer presents with abdominal bloating. A CT scan shows a large amount of ascites and diffuse, nodular, soft-tissue thickening of the omentum, giving it a solid, “cake-like” appearance.
Question: This diffuse, infiltrative thickening of the omentum is known as:
(A) The “Omental Cake” Sign (B) The “Comb Sign” (C) The “Accordion Sign” (D) The “Sister Mary Joseph Nodule” (E) The “Gut Gutter” Sign
Correct Answer: (A) The “Omental Cake” Sign.
Explanation:
- Why (A) is correct: The “omental cake” is the classic sign of peritoneal carcinomatosis. It refers to the diffuse, nodular thickening and infiltration of the greater omentum by metastatic deposits, causing it to appear as a solid “cake” of tissue. The most common primaries are ovarian, gastric, and colon cancer.
- Why (B) is wrong: The “comb sign” is for Crohn’s disease.
- Why (C) is wrong: The “accordion sign” is for C. difficile colitis.
- Why (D) is wrong: A Sister Mary Joseph Nodule is a palpable metastatic nodule at the umbilicus, not a diffuse omental finding.
- Why (E) is wrong: This is not a standard radiological term.
Key Points: Peritoneal Carcinomatosis
- Definition: Diffuse metastatic spread to the peritoneum.
- Classic Primaries: Ovarian, Gastric, Colonic, Pancreatic.
- CT Signs:
- “Omental Cake”: Diffuse, nodular thickening of the greater omentum.
- Peritoneal nodules and enhancement.
- Ascites (often high-density or loculated).
Question 14: Pneumoperitoneum
Stem: A 70-year-old man with a known duodenal ulcer presents with the sudden onset of severe, diffuse abdominal pain. A chest X-ray is performed.
Question: What is the most sensitive plain-film finding to look for in diagnosing a perforated viscus?
(A) Free air under the hemidiaphragm on an erect chest X-ray. (B) Dilated loops of small bowel. (C) The “coffee bean” sign. (D) Chilaiditi’s sign. (E) Rigler’s sign on a supine abdominal X-ray.
Correct Answer: (A) Free air under the hemidiaphragm on an erect chest X-ray.
Explanation:
- Why (A) is correct: An erect chest X-ray is the most sensitive plain-film investigation for pneumoperitoneum (free air in the abdomen), as small amounts of air will rise and be visible as thin, dark “crescents” under the diaphragm, contrasting with the dense liver and spleen.
- Why (B) is wrong: This is a non-specific sign of ileus.
- Why (C) is wrong: This is a sign of sigmoid volvulus.
- Why (D) is wrong: Chilaiditi’s sign is the interposition of the colon between the liver and diaphragm, which is a mimic of free air, not free air itself.
- Why (E) is wrong: Rigler’s sign (seeing both sides of the bowel wall, i.e., air on the outside as well as the inside) is a sign of pneumoperitoneum on a supine film, but it requires a large amount of air and is much less sensitive than an erect CXR.
Key Points: Pneumoperitoneum
- Definition: Free air in the peritoneal cavity, most often from a perforated viscus (e.g., duodenal ulcer, diverticulitis).
- Most Sensitive Plain Film: Erect Chest X-ray (or left lateral decubitus). Can detect as little as 1-2 cc of air.
- Supine X-ray Signs (Less Sensitive):
- Rigler’s Sign: Air on both sides of the bowel wall.
- Falciform Ligament Sign: Air outlining the falciform ligament.
Question 15: Tuberculous Peritonitis
Stem: A 35-year-old man, an immigrant from an endemic region, presents with 3 months of low-grade fever, weight loss, and abdominal distension. A CT scan shows high-density (proteinaceous) ascites, diffuse, smooth peritoneal enhancement, and bulky, low-density (caseous) mesenteric lymph nodes.
Question: This “wet-type” presentation is most characteristic of:
(A) Tuberculous Peritonitis (B) Pseudomyxoma Peritonei (PMP) (C) Peritoneal Carcinomatosis (D) Cirrhosis with Ascites (E) Omental Infarction
Correct Answer: (A) Tuberculous Peritonitis.
Explanation:
- Why (A) is correct: This is the classic “wet-type” of TB peritonitis. The key features are: 1) High-density ascites (protein- and cell-rich), 2) Smooth, uniform peritoneal enhancement, and 3) Bulky, low-density (caseating) lymphadenopathy.
- Why (B) is wrong: PMP is low-density mucinous ascites that causes visceral scalloping, not high-density ascites with enhancing peritoneum.
- Why (C) is wrong: Carcinomatosis causes nodular peritoneal enhancement (“omental cake”), not smooth enhancement.
- Why (D) is wrong: Cirrhotic ascites is simple, low-density (water) ascites and does not have peritoneal enhancement.
- Why (E) is wrong: This is a focal, inflammatory fat process.
Key Points: Tuberculous (TB) Peritonitis
- Definition: Peritoneal infection with Mycobacterium tuberculosis.
- “Wet Type” (Common):
- High-density, exudative ascites.
- Smooth, diffuse peritoneal enhancement (unlike the nodular enhancement of carcinomatosis).
- Low-density (caseating) mesenteric nodes.
- “Dry Type” (Fibrotic): Less ascites, more of a fixed, “omental-cake-like” mass (a “dry” omental cake).
