Which of the following is the best view for detecting minimal pneumoperitoneum?
Correct Answer: Left lateral decubitus abdominal x-ray with horizontal beam
Description: D i.e. Left lateral decubitus abdominal x-ray with horizontal beam Abdominal CT in lung window setting is the most sensitive investigation for detection of free peritoneal air pneumoperitoneum)Q followed by erect radiograph (i.e. erect x-ray chest PA view)Q f/b left lateral decubitus (with right side up) abdominal x-ray with horizontal beemQ f/b erect abdomen viewQ f/b supine abdomen viewQ. CT Scan Abdomen CTscan-abdomen is the most sensitive investigation for detection of free peritoneal air (i.e. pneumoperitoneum), intra abdominal or pelvic hemorrhage (hemoperitoneuni), spleen injury (commonest injured organ following blunt trauma abdomen), liver injury (2nd most common), adrenal injury (most common retroperitoneal injury) bowel and mesenteric injuries. Whereas, CT is relatively insensitive to acute pancreatic injuries. In order not to miss small (minimal) pneumoperitoneum, abdominal CT images should be viewed in the lung window settings. Bubbles of free air may be detected over the liver, anteriorly in mid abdomen, trapped between the leaves of mesentery or in the peritoneal recesses. Sentineal clot sign (i.e. clotted blood of higher attenuation 45-75HU) near the site of bleeding with lower attenuation and unclotted blood elsewhere in peritoneal cavity indicate hemoperitoneum. CT scan is the imaging modality of choice for diagnostic evaluation of abdominal trauma. CT is as accurate as DPL in detecting blunt abdominal injury with extra advantages of detailed anatomical evaluation of injuries, quantification of hemorrhage, detection of active aerial extravascation and better detection of retroperitoneal injuries. Wit these advantages diagnostic peritoneal lavage (DPL) has now almost become obsolete (to be used only in few hemodynamically unstable patients). Helical CT is preferred over conventional CT as it is fast, better (less aifacts & respiratory misregistration) and offers optimal IV contrast enhancement. Contrast enhanced CT is imaging modality of choice for spleenic & liver injuriesQ. MDCT provides excellent quality coronal, saggital reconstructions and is diagnostic modality of choice for detection of bowel & mesentric injuriesQ. Administration of IV iodinated contrast is mandatory as it makes detection & location of parenchymal contusions & hematoma more clear and identifies great vessels and provides information regarding integrity of organs or extent of the injury. Plain Radiography Erect chest radiographQ is superior to erect abdominal view for demonstration of pneumoperitoneumQ (i.e. free intra abdominal gas)Q since, in the later view, the divergent x-ray beam penetrates the gas between diaphragm and liver obliquely and this area is usually overexposed for detecting small amount of gases. - Erect chest film is best view for showing small pneumoperitoneum, paicularly on right side with gas under diaphragm because the X-ray beam is passing almost tangentially (horizontally) to the free gas and the exposure of diaphragm is optimal to show small amounts of gas. On the left it can be difficult to distinguish free gas from stomach & colonic gas. Number of conditions can simulate pneumoperitoneum on erect X-ray (k/a pseudo-pneumoperitoneum) such as Chilaiditi's syndrome (i.e. distended bowel b/w liver & diaphragm), subdiaphragmatic faVabscess,diaphragmatic irregularity, curvilinear lung collapse, intramural gas cysts in pneumatosis intestinalis, omental fat, distended viscus, subpulmonary pneumothorax, and apposition of gas distended loops mimicking the double wall sign. CT or lateral decubitus x-ray can differentiate by demonstrating gas b/w liver and abdominal wall. - Pneumoperitoneum can be detected in 76% of cases using an erect film only and in 90% cases if left lateral decubitus projection is also included. So in a suspected case a horizontal ray radiograph either an erect chest or left lateral decubitus (with right side up) abdomen X-ray, is mandatory. The patient should ideally remain in position for 10 min before the horizontal ray film is taken, because it takes this time for gas to rise to the highest point in the abdomen. In patients who are unfit to sit or stand for an erect film left lateral decubitus abdomenal radiograph is the projection of choice (i.e. 2nd best view) to show a small pneumoperitoneum. In this view free gas is seen b/w the edge of liver & lateral abdominal wall or sometimes over pelvis (in females, this may be the highest point). This is the best view to show a gas filled dialated duodenal loop, one of the commonest sign of acute pancreatitis. As little as lml of free gas can be demonstrated radiographically, on either an erect chest or a left lateral decubitus abdominal radiograph. A supine abdomen and an erect chest are regarded as basic standard radiographs in the acute abdomen. In many patients paicularly who are old, unconscious or critically ill, have suffered trauma, perforation (1/t pneumoperitoneum) may be clinically silent or is over shadowed by another serious medical or surgical condition, and the supine abdominal radiograph may be the only view that can be obtained. So it is impoant to be able to recognize the signs of pneumoperitoneum on supine view which are. Signs of right upper quadrant gas (best place to look for small collection) Doge's cap's sign is triangular collection of gas in Morrison's pouch (posterior hepatorenal fossa) Perihepatic (over the liver), subhepatic (postero inferior margin) and parahepatic (lateral to right edge) hyperlucency d/t gas Cupola/Mustache/Saddlebag sign is large amount of gas trapped below central tendon of diaphragm. Free gas may outline falciform ligament (most common), fissure of ligamentum teres (which is posterior free edge of falciform ligament k/a ligamentum teres sign) and ligamentum teres notch (inveed V shaped hyperlucent area along under surface of liver) Signs of large collection of gas - Football or air done sign is large amount of gas in center of abdomen over a fluid collection/or large pneumoperitoneum outlining entire abdominal cavity. - Rigler's double wall sign or bas-relief sign is visualization of both inner and outer walls of a bowel loop d/t air out lining both (luminal & serosal surface) is k/a Rigler's sign and the bowel loops then take on a ghost like appearance. - Tell tale triangular sign is small triangular collection of gas b/w 3 loops of bowel. - Free gas may outline & visualize diaphragmatic muscle slips, both lateral umblical ligaments (inveed V sign), medial umblical ligaments (containing obliterated umblical aeries) and middle umblical ligament (urachus sign). - Scrotal air through open processus vagnalis (in children)
Category:
Radiology
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