PLAIN ABDOMEN AND RETROPERITONEUM NITTHIDA BILLATEH, M.D. RADIOLOGY DEPARTMENT

STANDARD PLAIN FILMS Supine Upright AP view Alternative lateral decubitus view

Acute Abdomen series Abdominal supine position Gas pattern, calcification, soft tissue masses Abdominal upright position Free air, air-fluid level Chest upright position Free air Pneumonia at lung base Pleural effusion

Normal plain abdomen

Plain abdomen

Plain abdomen Supine Upright

How to look at a plain abdominal film Look for any dilated loops of bowel and try to decide which portions of the bowel are affected. Look for any gas outside the lumen of the bowel. Look for ascites and any soft tissue mass in the abdomen and pelvis. If there are any calcifications, try to locate exactly where they life. Assess the size of the liver and spleen.

Gas abnormalities

Normal bowel gas pattern The radiographic evaluation of intestinal gas Identification of the bowel segment containing the gas Assessment of the caliber of segment Assessment of most distal point of passage of the gas Evaluation of the mucosa outlined by the gas

Normal bowel gas in the supine film In the antrum and body of stomach Transverse colon, may be seen immediately inferior to the stomach Ascending and descending colon-lateral margin of peritoneal cavity Sigmoid-inferior aspect of abdomen Rectal gas, midline position in pelvis and extend to pubic symphysis.

Normal bowel gas in the supine film Stomach Almost always contains air or fluid Supine position: gas in stomach rises to the anteriorly located antrum while fluid gravitates to the fundus Upright: gas-filled fundus Valuable landmark for identifying space-occupying lesions in surrounding structures.

Normal bowel gas in the supine film Small intestine: central portion of the abdomen, smaller caliber than colon Plicae circulares or valvulae conniventis: 1-2 mm wide, interval 1 mm Less than 3 cm in diameter Colon: Peripheral portion of abdomen Haustra of the colon: 2-3 mm wide, interval 1 cm Less than 5 cm in diameter

Abnormal bowel gas pattern Gastric outlet obstruction Adynamic ileus Small bowel obstruction Colonic obstruction Closed loop obstruction Volvulus

Gastric outlet obstructuion

Gastric outlet obstructuion Antrum and pyloric region – usual site Most common cause: Peptic ulcer disease in distal stomach/duodenum with scarring Other cause: scirrhous gastric carcinoma, scarring from ingestion caustic substance

Gastric outlet obstruction Plain film depend on Degree of distention of stomach by air or fluid Duration of obstruction Position of patient Frequency of emesis Massively dilated fluid-filled stomach may mimic hepatomegaly or ascites Displace transverse colon inferiorly, characteristic contour Small amount of air: upright or right lateral decubitus film-confirm the gastric location of the fluid

Gastric outlet obstruction

Gastric outlet obstructuion Dilated stomch Dilated fluid-filled stomach Contrast cannot pass through distal passage PLAIN ABDOMEN SUPINE UPPER GI STUDY

Adynamic Ileus

Adynamic Ileus Dilated bowel, usually small intestine, absence of mechanical obstruction Absent or decreased intestinal peristalsis, which allows swallowed air to accumulate in dilated small intestine The present of colonic gas may be helpful in distinquishing from a mechanical obstruction

Adynamic Ileus Localized ileus Generalized ileus

Localized Ileus One or two persistently dilated loops of large or small bowel (sentinel loop) Gas in rectum or sigmoid Causes: acute appendicitis, acute cholecystitis, acute pancreatitis Pitfall: May resemble early mechanical SBO Clinical course Get follow up

Localized Ileus cholecystitis Pancreatitis Ulcer diverticulitis appendicitis Ureteral calculi

Generalized Ileus Gas in dilated small bowel and large bowel to rectum, long air-fluid levels Causes: electrolyte imbalances, sepsis, generalized peritonitis, blunt abdominal trauma, infiltration of the mesentery by tumor

Paralytic Ileus

Small bowel obstruction

Small bowel obstruction Duration of obstruction, frequency of emesis, use of NG-suction may effect the radiographic appearance 20% False positive and false negative rate No gas or fluid visible in small bowel of patients with high jejunal obstruction because of vomiting

Small bowel obstruction Causes: Most of small bowel obstruction are caused by postoperative adhesion (75%) Adhesion, may occur as early 1 wk after surgery Obstructing hernia(20%) 95% external hernia Internal hernia are uncommon Tumor Ectopic gallstones (2%) Acute appendicitis Intestinal parasite food

Small bowel obstruction Radiographic appearance Dilated small bowel loops: greater than 3 cm in diameter Air-fluid level at two different level in the same segment of bowel (different height in the same loop) Loops fill with air “stepladder” configuration Occasionally, “gasless” abdomen Small amount of air trapped between the plicae circulares in upright film “string of pearls or bead” (not seen in adynamic ileus)

Small Bowel Obstruction (SBO) Generalized dilated small bowel Different height in the same loop

Small Bowel Obstruction (SBO) Different height in the same loop Generalized dilated small bowel Step ladder pattern Supine: tense arch from RLQ to LUQ: step ladder pattern Different level of air fluid level in the same loop

Small Bowel Obstruction (SBO)

Small Bowel Obstruction (SBO)

String of pearl or bead String of beads sign

ลักษณะภาพถ่ายรังสี ลำไส้เล็กที่อยู่ก่อนถึงจุดอุดตันมีการขยายตัวใหญ่ขึ้น (small bowel dilatation) ส่วนใหญ่มักมีขนาดเส้นผ่าศูนย์กลางมากกว่า 2.5 ซม. (แต่ไม่เกิน 5.0 ซม.) ระดับความสูงของลม และน้ำ (air-fluid level) ที่แตกต่างกันในลำไส้ขดเดียวกัน (different height in the same loop) เป็นลักษณะที่ช่วยวินิจฉัยลำไส้เล็กอุดตัน อย่างไรก็ตามลักษณะนี้สามารถพบได้ในภาวะลำไส้อืด (รูปที่ 4) ไม่มีการขยายตัว และไม่มีลมอยู่ในลำไส้ใหญ่ เกิดลักษณะของความไม่ได้สัดส่วนกันระหว่างลมในลำไส้เล็ก และลำไส้ใหญ่ (disproportion of air between small bowel and large bowel) ลักษณะการวางตัวของลำไส้เหมือนขั้นบันได (step ladder pattern) เป็นลักษณะของลำไส้ที่ขยายใหญ่ และเรียงตัวขนานกันจากช่องท้องน้อยด้านขวาไปยังช่องท้องด้านซ้ายบน ลักษณะเช่นนี้เกิดจากลำไส้เล็กถูกยึดโดยเยื่อแขวนลำไส้ (mesentery) ที่วางตัวจากช่องท้องด้านขวาล่างไปที่ระดับไตด้านซ้าย (รูปที่ 5)

ลักษณะภาพถ่ายรังสี 5. ลักษณะลมเม็ดเล็กๆ เรียงตัวกันเหมือนสร้อยลูกปัด (string of bead) คือ การที่มีลำไส้เล็กอุดตันเป็นเวลานาน ทาให้เกิดการสะสมของของเหลวในลำไส้เพิ่มมากขึ้นร่วมกับปริมาณของลมในขดลำไส้ ลดน้อยลง ทำให้ลมที่เหลืออยู่ขังอยู่ระหว่างร่องของเยื่อบุลำไส้เล็ก (Valvular conniventis) เป็นเงาของลมเม็ดกลมๆ เรียงตัวกันเป็นแถวมีลักษณะเหมือนสร้อยลูกปัด (รูปที่ 6) 6. ไม่มีลมในช่องท้อง (gasless abdomen) หากเกิดการอุดตันเป็นเวลานานจะมีของเหลวเข้ามา

Colonic Obstruction Cause of colonic obstruction Primary adenocarcinoma of the colon (>50%) Diverticulitis stricture (15%) Colonic volvulus (10%) Inflammatory bowel disease Usually occur in sigmoid colon ( narrow caliber and more solid stool ) Carcinoma of cecum and ascending colon less likely to cause obstruction ( wider caliber, more liquid stool )

Colonic Obstruction Radiography Dilated gas-filled loops of colon proximal to the site of obstruction and paucity or absence of gas in the distal colon and rectum

Large Bowel Obstruction

Large Bowel Obstruction Absent rectal air, competent IC valve (closed loop)

Closed-Loop Obstruction Segment of bowel that is obstructed at two point Usually involve small bowel Causes: Adhesion Internal hernia Volvulus

Closed-Loop Obstruction Plain film: Nonspecific Occasionally, dilated, air-filled segment of bowel may assume a “coffee bean” configuration Persistence of an air-filled loop on sequential films for several days should suggest the possibility of a closed loop obstruction

Closed-Loop Obstruction Vascular compromise may lead to edema and thickening or effacement of the valvulae conniventis Clinical presentation: intermittent, crampy abdominal pain A definitive diagnosis can be made only at surgery

Sigmoid Volvulus Usually in elderly 60-70% of case colonic volvulus involves sigmoid colon

Sigmoid Volvulus The classic radiography: Dilated loop of sigmoid colon that has an inverted U configuration and absent haustra The dilated bowel commonly extends into the upper abdomen above transverse colon May be located in the midline or directed toward the right or left upper quadrant (mainly on left side) “Coffee bean” sign = distinct midline crease corresponding to mesenteric root in largely gas distended loop (supine)

Sigmoid Volvulus Contrast enema: smooth, tappered narrowing or “beaking” at rectosigmoid junction

Sigmoid Volvulus

Coffee Bean Sign

Sigmoid Volvulus

Sigmoid Volvulus

Beak sign in sigmoid volvulus

Cecal volvulus Rotational twist of the right colon on its axist associated with folding of the right colon, so that the cecum is located in the midabdomen or LUQ Less common than sigmoid volvulus

Cecal volvulus Cause: Incidence: about 40% of colonic volvulus. Sudden distension by trauma, pressure constipation, distal colonic obstruction Incidence: about 40% of colonic volvulus. Age peak: 20-40 year Associated with malrotation(10-25% of case)

Cecal volvulus Plain film: Dilated, air-filled cecum in an ectopic location, cecal apex in the LUQ The medially placed IC valve may produce a soft tissue indentation  gas-filled cecum (coffee bean or kidney) Barium enema: beak sign at mid ascending colon

Cecal volvulus

Soft tissue abnormalities

Liver RUQ of the abdomen 20-22 cm in its greatest transverse dimension 15-17 cm in its greatest vertical dimension The hepatic angles may obscured by effusions or blood that infiltrates the retroperitoneal fat or because ascites, which displaces the liver edge away from the adjacent fat.

Liver Hepatomegaly: elevation of right hemidiaphragm, inferior displacement of the hepatic flexure of the colon lateral displacement of the lesser curvature of stomach displace inferior edge of the liver beyond right margin of psoas muscle inferior displacement of the right kidney

Hepatomegaly Inferior displacement of the hepatic flexure of the colon Inferior liver margin Inferior liver margin

Gallbladder A shallow fossa on the inferior surface of the liver between the right and left lobes and is not often visualized on plain films. Superior and lateral to the duodenal bulb and gastric antrum and superior to the proximal transverse colon

Gallbladder Occasionally, the fundus may be visualized in normal patients if it indents the surrounding fat Only 15% of gallstones are sufficiently calcified to be seen on plain film

Spleen LUQ, beneath the left hemidiaphragm and posterior-lateral to the gastric fundus 12 cm in length, 7 cm in width The outline of spleen in plain radiograph cannot be identified in 42% of normal subject

Spleen Splenomegaly: A soft tissue mass extending downwards and medially from LUQ elevation of left hemidiaphragm, medial displacement of the gastric air bubble and left kidney splenic tip below the costal margin Inferior displacement of colon Inferior margin of spleen

Hepatosplenomegaly

Pneumoperitoneum

Pneumoperitoneum As little as 1 ml of air could be detected below the RT.hemidiaphragm on properly exposed upright chest film Plain film for detection free air Chest upright (most sensitive forpneumoperitoneum) Left lateral decubitus Lateral cross table view

Cause of pneumoperitoneum Trauma Abdominal surgery Anastomotic leakage Peritoneal tap Endoscopy biopsy Penetraing injury Percutaneous endoscopic gastrostomy Bowel Perforation of benign ulcer Perforation of neoplasm Perforation of appendix Jejunal diverticulosis Diverticulosis of sigmoid colon

Pneumoperitoneum On supine abdominal films must be able to recognize the intraperitoneum air, based on following sign Serosal or Rigler’sign Increased lucency in the RUQ Triangular sign Visualization of the undersurface of the diaphragm Air in the Morison pouch Outline of the normal peritoneal ligament “ Football ” sign Air in the lesser sac of peritoneal cavity

Pneumoperitoneum

Pneumoperitoneum Double bowel wall sign Falciform ligament sign

Pneumoperitoneum

Rigler sign Double bowel wall sign

Increase lucency in RUQ

Air in Morison pouch

Falciform ligament sign

Pneumoperitoneum Foot ball sign

Triangular sign

Pneumoretroperitoneum Gas that enters the retroperitoneal spaces Usually easily distinquished from intraperitoneal gas bound by fascial plane, linear fashion along the margins of the psoas muscle, the renal outlines and medial undersurface of hemidiaphragm

Pneumoretroperitoneum Causes: Ruptured or perforation of retroperitoneum organ Ulcer, injury, diverticulitis, blunt abdominal trauma Location of the retroperitoneal gas may provide a clue to its origin Duodenal perforation: confined to the right anterior pararenal space

Pneumoretroperitoneum a retroperitoneal perforation with air outlining the liver edge, right kidney and the psoas muscle edge (arrow).

Pneumobilia Gas in the bile duct Thin, branches, tubular areas of lucency in the central portion of the liver Almost always result from communication between bile duct and intestine

Pneumobilia Cause Post op biliary-enteric fistula choledochojejunostomy Penetrate duodenal ulcer Emphysematous cholecystitis Recent passage of common duct stone

Pneumobilia

Portal venous gas Thin, branching, tubular areas of lucency occupy the periphery of the liver and extend almost to the liver surface Cause: Intestinal ischemia or infarction Dilatation of stomach and bowel

Intramural gas (pneumatosis intestinalis) Gas in wall of the intestine Two radiographic pattern Bubbly Thin or linear streaks of gas In combination with portal venous gas, linear gas collections in the intestinal wall are almost always a sign of bowel infarction in adult patient

Pneumatosis intestinalis

Intramural gas Emphysematous gastritis

Pneumatosis cystoides coli Rare benign condition: multiple gas-filled bleb or cysts in the wall of colon Grapelike clusters of gas, usually segmental in distribution Left colon > right colon

Ascites Only large amount of ascites can be identified on abdominal radiographs Plain abdominal findings of ascites Obliteration of inferior edge of the liver Widening of the distance between the flank stripe and the ascending colon Medial displacement of the lateral edge of the liver Fluid accumulation in the pelvis

Ascites Plain abdominal findings of ascites (cont.) Separation of the bowel loops Centrally located bowel loops with bulging flanks Ground-glass appearance

Ascites

Ascites

Ascites

Abnormal Calcifications Gallstone KUB stone Calcified organs Pancreas, nodes Calcified old granuloma: liver, spleen Calcified mass

Gallstones GS: investigation of choice: US Renal stone: investigation of choice: plain KUB DDx: lateral view

Gallstones sand stones Sandstones in GB and cystic ducts

Calcified Pancreas

Calcified Nodes

Calcified Splenic Granuloma

Calcified Uterine Fibroid

Retroperitoneum Intra-abdominal tissue planes and visceral surfaces are visible on plain films- surrounding fat Identifying normal anatomic structures and in recognizing and localizing pathologic process

Retroperitoneum space Lies posterior to the parietal peritoneum and anterior to the transversalis fascia Divided into three disinct compartment Anterior pararenal space Perirenal space Posterior pararenal space

Anterior pararenal space Lie anterior to the perirenal space and lateroconal fascia Retroperitoneum duodenum Pancreas Ascending and descending colon

Perirenal space Confined by anterior and posterior layer of renal fascia Contains: Kidneys Adrenal glands Abundant fat Perirenal fat allows plain film visualization of the renal outlines in most patient

Perirenal space Perirenal fat is responsible for plain film visualization of the upper half of the psoas muscle and medial aspect of the hepatic and splenic angles Obliteration of perirenal fat: inflammation, blood or urine. Medially, the perirenal space is in continuity with the aorta and often fills with blood in patient with ruptured aortic aneurysms.

Perirenal space Laterally, anterior and posterior layers of perirenal fascia fuse to form the lateroconal fascia, which continues laterally and ventrally to fuse with parietal peritoneum along lateral abdominal wall

Posterior pararenal space Lies posterior to the posterior perirenal and lateroconal fascia and anterior to the transversalis fascia lining the abdominal wall Contains variable amount of fat, but no organs Medially, the posterior pararenal space originate at the lateral margin of the psoas muscle and is not continuous across the midline

Posterior pararenal space Laterally, the posterior pararenal fat continues around the flank to become continuous with properitoneal fat of the lateral abdominal wall, forming the “flank stripe” Posterior pararenal fat is continuous inferiorly with extraperitoneal fat in the pelvis.

Psoas muscle Arise from the T12-L5 vertebrae Extends inferiorly to join the iliac muscle below the iliac crest and continues as the iliopsoas muscle to the lesser trochanter Lateral margin: outlined by perirenal fat superiorly and posterior pararenal fat below the level of the kidney About 19% of normal individuals have a blurred right psoas outline.

Psoas muscle Blood or inflammatory exudate in the adjacent retroperitoneal fat may cause obliteration of the margin of the psoas muscle. Absence of the psoas margin on plain films must be interpreted with caution Lumbar scoliosis Rotation of the spinal column Fluid-filled bowel loop Normal variation

Reference Richard M. Gore, M.D. Gastrointestinal radiology second edition Michael P. Federle, M.D. Diagnostic Imaging Abdomen first edition