Gastrointestinal System





Introduction


Imaging Techniques and Anatomy


The most common imaging study of the abdomen is referred to as a KUB, or plain image of the abdomen. The term KUB is historical nonsense. It stands for k idney, u reter, and b ladder, none of which is usually seen on a regular x-ray of the abdomen; nevertheless, the term remains widely used. A KUB is usually done with the patient supine ( Fig. 6.1 ). When examining this image, you should look at the bony structures, the lung bases, and then the soft tissue and gas patterns ( Box 6.1 ). The soft tissue pattern analysis should include evaluation of the lateral psoas margins. Whether you see them bilaterally, only faintly, or throughout their length depends on the shape of the psoas and the amount of retroperitoneal fat in that individual. It is all right if you do not see the psoas margin on either side. If you see the psoas margin on one side but not on the other, this is most commonly due to normal anatomic variation. In about 25% of cases, however, pathology will be found on the side of the obscured psoas margin.




Fig. 6.1


Normal Anatomy Seen on a Supine X-Ray (KUB) of the Abdomen.


Box 6.1

Items to Look for on a Plain Abdominal Radiograph (KUB)


Gas Patterns





  • Stomach, small bowel, and rectosigmoid



  • Abnormal or ectopic collections



Organ Shapes and Sizes





  • Liver



  • Spleen



  • Kidneys



  • Soft tissue pelvic masses



Other





  • Calcification



  • Asymmetric psoas margins



  • Skeleton



  • Basilar lung abnormalities



KUB , Kidney, ureter, bladder.



Even though they are difficult to see, you should look for the outlines of the kidneys. Again, if you cannot see the outlines, you should not be terribly concerned, because they are often obscured by overlying bowel gas and fecal material. The liver is seen as a homogeneous soft tissue density in the right upper quadrant. The spleen can sometimes be seen as a smaller homogeneous density in the left upper quadrant. Although you will be able to appreciate massive enlargement of either one of these organs, minimal to moderate enlargement is very difficult to ascertain, and you should think twice before you suggest it. Clinical palpation and percussion are at least as accurate as x-rays in this situation.


Evaluation of the gas pattern also is important ( Box 6.2 ). Because people routinely swallow air and drink lots of carbonated beverages, the stomach almost always has some gas in it. When a person is lying on his or her back, the air will go to the most anterior portion of the stomach, which is the body and antrum. This is seen as a curvilinear air collection, just along the left side of the upper lumbar spine ( Fig. 6.2 ). If the person has swallowed a lot of air, you may see gas bubbles within the entire gastrointestinal (GI) tract, extending from the stomach to the rectum. The origin of almost all these bubbles is swallowed air and not gas produced by intestinal bacteria. You should be able to identify the air patterns in the stomach, small bowel, colon, sigmoid, and rectum. Gas in the small bowel usually can be identified because small bowel mucosa has extremely fine lines that cross all the way across the lumen. Most small bowel gas is located in the left midabdomen and the lower central abdomen. The colon often can be traced from the cecum in the right lower quadrant to both the hepatic and splenic flexures and down to the sigmoid. The cecum and the colon often have a bubbly appearance, representing a mixture of gas and fecal material. Colonic air often has a somewhat cloverleaf-shaped appearance caused by the haustra of the colon. The normal small bowel diameter should not exceed 3 cm, and the colon should not exceed 6 cm. The cecum can normally be somewhat larger than the rest of the colon and may be up to 8 cm in diameter.



Box 6.2

Evaluation of Gas Patterns on a Plain Radiograph of the Abdomen


Collections Normally Present





  • Look for dilatation of structure and assessment of wall or mucosal thickness in stomach, small bowel, colon, and rectosigmoid



Collections Not Normally Present





  • Free air under the diaphragm (upright image)



  • Free air on supine radiograph (double bowel wall sign)



  • Right upper quadrant: portal vein (peripheral in liver), biliary system (central in liver)



  • Small bubbles in an abscess



  • Emphysematous cholecystitis, pyelonephritis, or cystitis





Fig. 6.2


Normal Bowel Gas Pattern.

Gas is normally swallowed and can be seen in the stomach (St) . Small amounts of air normally can be seen in the small bowel (SB) , and this is usually in the left midabdomen or central portion of the abdomen. In this patient, gas can be seen throughout the entire colon, including the cecum (Cec) . Where the air is mixed with feces, a mottled pattern appears. Cloverleaf-shaped collections of air are seen in the hepatic flexure (HF) , transverse colon (TC) , splenic flexure (SF) , and sigmoid (Sig) .


In addition to a supine abdominal image, a three-way view of the abdomen is often obtained. The additional two views are an upright posteroanterior (PA) chest x-ray and a view of the abdomen taken with the patient standing upright. The PA view of the chest is taken to look for chest pathology that may be mimicking or causing abdominal symptoms, as well as to look for free air underneath the hemidiaphragms. The reason for the standing view of the abdomen is to look at the air-fluid levels within the bowel to differentiate between an obstruction and an ileus.


A common variant is called colonic interposition (also called Chilaiditi syndrome ). In this normal variant, the hepatic flexure of the colon can slip up between the superior aspect of the liver and the dome of the right hemidiaphragm ( Fig. 6.3 ). This should not be mistaken for free air. When colonic interposition occurs, you can almost always see the haustral markings of the colon.




Fig. 6.3


Colonic Interposition.

This is a normal variant in which the hepatic flexure can be seen above the liver. This is seen as a gas collection under the right hemidiaphragm (arrow) , but it is clearly identified as colon, owing to the transverse haustral markings.


Computed tomography (CT) scanning is the most common procedure used to image abdominal pathology. The visualization of the solid organs, peritoneum, and retroperitoneum that is obtained with CT means that CT is being ordered as much as or more than plain abdominal radiographs. CT anatomy is presented in Fig. 6.4 . With new scanners, the entire pelvis and abdomen can be imaged in a few seconds. For evaluation of the solid organs, imaging may be done with or without iodinated intravenous (IV) contrast agents. For evaluation of suspected pathology in the stomach, small intestine, colon, or rectum, the lumen can be differentiated by using orally administered contrast agents, either dilute barium or just water.




Fig. 6.4


Normal Transverse Computed Tomography Anatomy of the Abdomen and Pelvis.

(A–L) The patient has been given oral, rectal, and intravenous, contrast media.

Ant , Anterior.








Patients commonly prepare by drinking oral contrast about 1 to 3 hours before the examination. If pelvic pathology is suspected, rectal contrast is occasionally given at the time of the examination.


With CT virtual colonoscopy, a three-dimensional (3D) reconstruction of the abdomen is generated, and the computer is used to create images that track the inside of the colon. This technique requires that the colon be well cleaned so that small bits of fecal material are not mistaken for polyps. True colonoscopy has the advantage that if a lesion is seen, a biopsy can be performed.


Ultrasound examination is used primarily to image the liver, kidneys, gallbladder, common bile duct, and, to a much lesser extent, pancreas and appendix. Ultrasound is often limited by the inability of the sound to penetrate air and by large loops of bowel that may obscure underlying pathology. Ascites is easily detected and localized for paracentesis.


Magnetic resonance imaging (MRI) is being used more frequently than in the past for both abdominal and pelvic pathology. It tends to be more useful in adults than children and for solid organs that have little motion during the examination. As with ultrasound, there is an advantage because neither uses ionizing radiation. Often it is necessary to use IV contrast (such as gadolinium). Imaging of the bowel is often less than satisfactory.


Nuclear medicine scans provide physiologic information that is often not available using other imaging techniques. They are often used to quantitate gastroesophageal reflux and gastric emptying times, diagnose acute cholecystitis and bile leaks, determine the site of GI bleeding, and stage tumors.


Pneumoperitoneum


It is easiest to identify small amounts of free air in the peritoneal cavity by doing an upright chest x-ray. In this manner, as little as 3 or 4 mL of air may be visualized ( Fig. 6.5A ). An upright abdominal radiograph is usually not especially useful to look for free air because the domes of the diaphragms are often off the upper edge of the image. It is extremely difficult to appreciate even relatively large amounts of free air within the peritoneal cavity by looking at a supine (KUB) view of the abdomen. If a lot of free air is present, you may be able to see the bowel wall outlined by air (see Fig. 6.5B ). If the patient is too sick to stand and you suspect a small pneumoperitoneum, order a left lateral decubitus view of the abdomen. In this manner, with the patient lying on the left side (for 10–15 minutes), small amounts of air can be seen tracking up over the lateral aspect of the right lobe of the liver. Tiny amounts of free air can be detected on CT scans (see Fig. 6.5C ).




Fig. 6.5


Pneumoperitoneum.

(A) A few milliliters of free air can be identified (arrows) under the right hemidiaphragm on this upright posteroanterior chest x-ray. (B) A supine abdominal radiograph obtained on a different patient with massive pneumoperitoneum shows the bowel wall (arrows) outlined on both sides by air. (C) In a different patient, a tiny amount of free air (arrow) anterior to the liver can easily be seen on a CT scan.


Intra-Abdominal Abscesses and Fever of Unknown Origin


Air can be seen within some, but by no means all, abscesses. Although an extremely large abscess may be appreciated on a plain radiograph, it is often difficult to tell whether you are looking at air in the bowel or in some other structure. For this reason, the imaging test of choice when an abdominal or pelvic abscess is suspected is a CT scan ( Fig. 6.6 ). It is important that under these circumstances you order a CT scan with GI contrast so that the entire bowel can be filled with contrast. If this is not done, it may be difficult, even on a CT scan, to differentiate a collection of bowel that has air and fluid in it from an abscess.




Fig. 6.6


Hepatic Abscess.

This drug abuser initially was seen with right upper quadrant pain and fever. (A) On the upright chest radiograph, a collection of air is seen in the right upper quadrant. Note the thick and irregular margin between the air and the hemidiaphragm, indicating that this is not free air. (B) A transverse computed tomography scan shows an air and pus collection due to a large abscess in the right lobe of the liver.


The imaging workup of a patient with a fever of unknown origin usually begins with a chest x-ray. Most infectious processes of the chest are quite obvious. Once intrathoracic pathology has been excluded, the next place to look is the abdomen and pelvis. Assuming that the physical examination of the abdomen and pelvis is negative, a CT scan is usually ordered.


Feeding Tubes


As mentioned in Chapter 3 , feeding tubes and nasogastric tubes are particularly recalcitrant medical devices. Not only can they inadvertently be passed into the trachea and major bronchus, but also they love to coil in the pharynx and stomach. On the plain radiograph, a well-placed enteric (Dobbhoff) feeding tube can be seen coming down the esophagus, passing in an arc through the stomach toward the right of midline, and then progressing downward in a reverse arc through the duodenum, back to the left, and across the vertebral column. It is best to have the tips of these feeding tubes near the junction of the duodenum and jejunum (ligament of Treitz; Fig. 6.7 ). An unacceptable position of a feeding tube tip is in the esophagus or at the gastroesophageal junction ( Fig. 6.8 ). If you feed patients with a tube in these positions, esophageal reflux and the potential for aspiration can occur.




Fig. 6.7


Optimal Positioning for an Enteric Feeding Tube.

On an anteroposterior radiograph of the upper abdomen, the feeding tube should be seen extending down the esophagus (E) slightly to the left of midline, taking a gentle curve to the right through the stomach (St) , and then reversing its curve through the duodenum (D) and going back to the left across the spine to the junction of the fourth portion of the duodenum and the jejunum (ligament of Treitz).



Fig. 6.8


Unacceptable Position of Feeding Tube.

In this case, the tip of the feeding tube is in the distal esophagus, with the remainder coiled in the body of the stomach. Feeding with the tube in this position is likely to cause aspiration.


Abdominal Calcifications


Abdominal calcifications are quite common, and you should be familiar with them so that you know which are important and which to discount ( Box 6.3 ). Fortunately, most of them have some characteristics that make this task relatively easy. Calcifications in the right upper quadrant are usually gallstones or kidney stones. If the calcifications are multiple, are close together, and lie outside the normal expected area of the kidney, you can be reasonably sure that they are gallstones ( Fig. 6.9 ). A single calcification in the right upper quadrant may be due to either a kidney stone or a gallstone. A simple way to tell the difference is to take a right posterior oblique view. A gallstone will rotate anteriorly and will not move with the outline of the kidney. Another way to tell the difference is to order a right upper quadrant ultrasound study, on which gallstones are easily identified ( Fig. 6.10 ). In addition, if the patient has right upper quadrant pain or jaundice, the ultrasound image will allow you to assess whether the common bile duct is dilated and look at the internal architecture of the liver and pancreas.



Box 6.3

Differential Diagnosis of Abdominal Calcifications


Right Upper Quadrant





  • Gallstones



  • Renal calculus, cyst, or tumor



  • Adrenal calcification



Right Midabdomen or Right Lower Quadrant





  • Ureteral calculi



  • Mesenteric lymph node



  • Appendicolith



Left Upper Quadrant





  • Splenic artery



  • Splenic cyst



  • Splenic histoplasmosis (multiple and small)



  • Renal calculus, cyst, or tumor



  • Adrenal calcification



  • Tail of pancreas



Central Abdomen





  • Aorta or aortic aneurysm



  • Pancreas (chronic pancreatitis)



  • Calcified metastatic nodes



Pelvis





  • Phleboliths (low in pelvis)



  • Uterine fibroids (popcorn appearance)



  • Dermoid



  • Bladder stone



  • Calcifications in buttocks from injections



  • Prostatic (behind symphysis)



  • Vas deferens (diabetic)



  • Iliac or femoral vessels





Fig. 6.9


Multiple Gallstones.

Any collection of grouped calcifications in the right upper quadrant (arrows) is most likely due to gallstones but does not indicate acute cholecystitis.



Fig. 6.10


Single Gallstone.

(A) On the KUB (plain radiograph of the abdomen), a single calcification is seen in the right upper quadrant (arrow) . It is not possible to tell from this one picture whether this is a gallstone, kidney stone, or calcification in some other structure. (B) A longitudinal ultrasound image in this patient clearly shows the liver, gallbladder (GB) , and an echogenic focus (arrow) within the gallbladder lumen, representing the single gallstone. Also note the dark shadow behind the gallstone. (C) Another longitudinal ultrasound image slightly more medial also shows the inferior vena cava (IVC) and the common bile duct (CBD) , which can be measured. Here it is of normal diameter.

Ant , Anterior.


Left upper quadrant calcifications are essentially always related to the spleen. Multiple small punctate calcifications are the result of histoplasmosis ( Fig. 6.11 ). Serpiginous or rounded calcifications in the left upper quadrant usually are related to splenic artery calcification or a splenic artery aneurysm ( Fig. 6.12 ).




Fig. 6.11


Splenic Histoplasmosis.

Multiple small rounded calcifications in the left upper quadrant (some of which are shown with small arrows ) are very specific, representing previous infection with histoplasmosis. These are of little, if any, clinical significance.



Fig. 6.12


Splenic Vascular Calcifications.

(A) Serpiginous calcifications (arrows) in the left upper quadrant are almost always due to splenic artery calcification. This finding is of no clinical significance. (B) Occasionally, a splenic artery aneurysm may cause a shell-like rounded left upper quadrant calcification. NG , Nasogastric.


With chronic pancreatitis, calcification of the pancreas often is found. This can be seen as spotted or mottled calcification, usually lying in a somewhat horizontal distribution over the vertebral bodies of L1 and L2 extending to the left. Remember, however, that on a plain abdominal x-ray, most persons with chronic pancreatitis do not have visible calcifications. CT scanning can identify calcifications much more easily than can a standard x-ray ( Fig. 6.13A ), but you should rely on the clinical and laboratory history, not on a CT scan (see Fig. 6.13B ), for the diagnosis of chronic pancreatitis.




Fig. 6.13


Calcification in Chronic Pancreatitis.

(A) Rarely, on a plain radiograph of the abdomen, a horizontal band of calcifications can be seen extending across the upper midabdomen (arrows) . (B) Calcification within the pancreas is much easier to see on a transverse computed tomography scan of the upper abdomen. Calcification is seen as white speckled areas within the pancreas (arrows) . The darker areas within the pancreas represent dilated common and pancreatic ducts.

Ant , Anterior; GB , gallbladder; K , kidney; L , liver; Sp , spleen; St , stomach.


Calcification of mesenteric lymph nodes can occur as a result of previous infections. These are usually seen as somewhat rounded or popcorn-shaped calcifications in the right midabdomen. A tip-off is the significant downward movement of these calcifications on the upright views because the mesentery is very mobile ( Fig. 6.14 ).




Fig. 6.14


Calcification in the Mesenteric Lymph Nodes.

This is a benign finding. (A) The calcifications are typically located in the midabdomen to the right of midline, are somewhat popcorn-shaped (arrow) , and are relatively easy to see on a supine KUB. (B) On an upright view of the abdomen, these calcifications drop substantially owing to the mobility of the mesentery.


In a patient who has right lower quadrant pain, look carefully in this area for calcifications. A stone within the appendix (appendicolith) often projects over the right side of the sacrum ( Fig. 6.15 ) and can be difficult to see unless you look carefully. An appendicolith is present in approximately 10% of patients with appendicitis and, if you see an appendicolith, a high probability of appendicitis exists. Other signs of appendicitis are a bubbly gas collection (appendiceal abscess) in the right lower quadrant or a focal ileus (dilatation) of the nearby small bowel caused by the inflammatory reaction.




Fig. 6.15


Appendicolith.

This calcification within the appendix can be seen almost anywhere in the right lower quadrant but is especially difficult to see when it overlies the sacrum (arrows) . A right lower quadrant calcification in a patient with pain in this area should carry an extremely high clinical suspicion of acute appendicitis.


In adults, it is common to see rounded calcifications in the lower half of the pelvis. These almost always are 1 cm or less in diameter, and they are phleboliths (calcifications within pelvic venous structures). They are easy to identify because they often have a lucent or dark center ( Fig. 6.16 ). They can occasionally be confused with stones in the distal ureter and, if a patient has symptoms of renal colic or obstruction, it is often necessary to perform a noncontrast CT to determine which of the calcifications in the lower pelvis may be phleboliths or calculi.




Fig. 6.16


Phleboliths.

These rounded vascular calcifications within the pelvis (arrow) are common and are of no clinical significance. They are usually round and less than 1 cm in diameter. They often have a lucent or dark center. They are typically seen in the lower half of the pelvic brim and can occasionally be difficult to differentiate from ureteral calculi without a CT scan.


Uterine fibroids can often be calcified. This type of calcification is similar to the popcorn type seen in the mesenteric lymph nodes. The difference is that fibroids are located in a suprapubic position and centrally in the pelvis. On occasion, these can be quite large and spectacular ( Fig. 6.17 ).




Fig. 6.17


Calcified Fibroids.

Central pelvic calcifications, which are somewhat amorphous, most commonly represent fibroids (arrows) .


Two special types of calcification can be seen in the male pelvis. The first, prostatic calcifications, are found immediately behind the symphysis pubis. They are quite common and are the result of benign inflammatory disease. They are not associated with prostate cancer ( Fig. 6.18 ). The second and rarer type of calcification looks like a little set of antlers in the middle of the pelvis, projecting slightly above the symphysis pubis. This represents calcification of the vas deferens and almost always indicates that the patient has diabetes ( Fig. 6.19 ).




Fig. 6.18


Prostatic Calcification.

A calcification situated immediately behind the pubis (arrows) in a male patient usually represents the sequelae of previous prostatitis.



Fig. 6.19


Calcification of the Vas Deferens.

These bilateral asymmetric calcifications occur in the lower to middle portion of the male pelvis (arrows) . When they are seen, they almost always indicate that the patient has diabetes.


Acute Abdominal Pain


Acute atraumatic abdominal pain requires urgent evaluation. Evaluation of the location, onset, progression, and character of abdominal pain is necessary to begin developing a reasonable differential diagnosis. A thorough medical history and physical examination are necessary because abdominal pain may be associated with GI, genitourinary, cardiovascular, or respiratory disorders. An electrocardiogram may be necessary to exclude myocardial causes. In addition to a physical examination of the chest and abdomen, pelvic and rectal examinations also may yield useful information. Sudden onset of pain is often associated with bowel perforation, ruptured ectopic pregnancy, ovarian cyst, aneurysm, or ischemic bowel. Gradually increasing and localizing pain is more common in appendicitis, cholecystitis, and bowel obstruction.


After the patient has been assessed clinically, a reasonable approach to imaging can be formulated. In most cases of acute abdominal pain, the best initial imaging study is an upright PA chest x-ray and a supine and upright view of the abdomen and pelvis with IV contrast (the so-called three-way abdomen). CT scanning is used when an abscess, aneurysm, or retroperitoneal pathology is suspected. Ultrasound is the best initial examination if a gallbladder, obstetric, or gynecologic cause is suspected.


Abdominal Trauma


The imaging done in cases of abdominal trauma depends largely on whether the trauma is blunt or penetrating and whether the patient is stable or unstable and how soon surgery may need to be done. If the patient is unstable, usually chest, abdomen, and pelvis radiographs are done. These can show free air, pneumothorax, pneumomediastinum, fractures, and metallic foreign bodies. This can be followed by f ocused a bdominal s onography for t rauma (so-called FAST ultrasound) to look for pericardial, pleural, and free peritoneal fluid. If the FAST scan is positive, surgery often follows. If there is penetrating trauma and the FAST scan is negative, surgery may still be necessary. If the patient is hemodynamically stable, a CT scan of the abdomen and pelvis with contrast may be done. If there is significant hematuria, this should be followed with CT cystogram.


Acute Gastroenteritis


A diagnosis of acute gastroenteritis is made on the basis of clinical history and the presence of diarrhea. The patient also may have vomiting, nausea, and abdominal pain. Dehydration is a common complication. The only procedure recommended is flexible sigmoidoscopy if blood is present in the stool.


Abdominal Masses


Palpable abdominal masses can arise from any organ or structure in the peritoneal space, retroperitoneum, aorta, bowel, pelvis, or abdominal wall. As a general rule, most abdominal masses do not grow down into the pelvis, but pelvic masses (being largely confined) often grow up into the abdomen. The initial imaging study should be a three-way view of the abdomen to look for associated thoracic pathology (such as metastases or effusions), abnormal gas collections, displacement of the bowel, renal outlines, or associated calcification. Although ultrasound imaging can be used to characterize an abdominal mass, in adults, CT scanning of the abdomen and pelvis with IV and oral contrast is usually obtained. Ultrasound is preferred for initial imaging in children.




Esophagus


Anatomy and Imaging Techniques


The appropriate initial imaging study for a number of suspected clinical problems is shown in Table 6.1 . Imaging of the esophagus for many problems is best done by direct visualization (endoscopy). Because this is a major procedure requiring sedation, many physicians begin by ordering an upper GI examination or contrast esophagogram. In addition to barium, other water-soluble contrast materials can be used. If a tear or perforation of the esophagus is suspected, it is best initially to use water-soluble contrast material rather than barium. If aspiration is suspected, barium is used because water-soluble contrast can irritate the lung.



TABLE 6.1

Initial Study to Order for Various Clinical Problems



































































































































































Suspected Clinical Problem Imaging Study
Gastroesophageal reflux
Mild or transient Medical therapy
Severe or persistent Endoscopy with biopsy
Esophageal obstruction or dysphagia Barium swallow (biphasic esophagogram)
Esophageal tear Meglumine diatrizoate (Gastrografin) swallow
Bowel perforation or free air Upright chest and supine abdominal plain radiograph; supine and left lateral decubitus, if patient is unable to stand
Hematemesis Endoscopy (less preferred, contrast UGI series)
Gastric or duodenal ulcer Test for Helicobacter pylori ; if medical therapy fails, endoscopy or double-contrast UGI series
Trauma, blunt or penetrating If patient unstable, chest, abdomen, and pelvis x-ray, US of abdomen and pelvis for free fluid; if stable, CT of abdomen and pelvis with IV contrast
Palpable abdominal mass CT of abdomen with IV contrast or MRI of abdomen with and without IV contrast
Abdominal aortic aneurysm Supine and lateral view of abdomen, then US or CT with IV contrast
Acute pancreatitis (stable patient, first episode) US of abdomen
Pancreatitis (critically ill) CT of abdomen with contrast
Pancreatic pseudocyst follow-up CT or US
Acute nonlocalized abdominal pain with fever (suspect abscess) CT of abdomen and pelvis with IV contrast; US or MRI for pregnant patient
Liver lesion MRI of abdomen with and without IV contrast
Acute cholecystitis US or nuclear medicine hepatobiliary scan
Chronic cholelithiasis Right upper quadrant US
Common duct obstruction Right upper quadrant US
Jaundice
Painful US or CT with and without IV contrast
Painless, suspect biliary obstruction CT with IV contrast, US of abdomen or MRI of abdomen with and without contrast with MCRP
Painless, suspect liver US
Suspected bile leak Nuclear medicine hepatobiliary study
Small bowel stricture or polyp CT enterography
Intestinal obstruction Supine and upright radiograph of abdomen as initial study, followed by those listed below:
Esophagus or stomach obstruction UGI and small bowel series or endoscopy
Small bowel obstruction CT of abdomen and pelvis with IV contrast
Distal small bowel or colon obstruction Barium enema
Crohn disease CT with IV contrast or CT enterography
Right upper quadrant pain US of abdomen
Appendicitis
Adults CT abdomen and pelvis with IV contrast (US for pregnant female)
Children < 14 years US-graded compression; CT of abdomen and pelvis with contrast if negative or equivocal US
Left lower quadrant pain, suspected diverticulitis CT of abdomen and pelvis with IV contrast
Suspected pelvic abscess CT with IV contrast or US
Ulcerative colitis Colonoscopy (see text for screening); if incomplete or unavailable, barium enema
Ischemic colitis CT with IV contrast
Suspected renal or ureteral stone Noncontrast CT
Pelvic pain (female) US
Bladder pathology Cystoscopy; if not available, CT cystogram
Uterine or ovarian pathology US
Abdominal tumor CT with IV contrast
Colon cancer Colonoscopy (see text for screening); if incomplete, double-contrast barium enema
Acute diverticulitis (left lower quadrant pain) CT with IV contrast
Rectal Bleeding (obvious)
Dark red Esophagogastroduodenoscopy; if not available, UGI series
Bright red Colonoscopy
Unknown source or colonoscopy nondiagnostic Nuclear medicine bleeding study
Positive fecal occult blood test
> 40 years Colonoscopy
< 40 years with GI symptoms Helicobacter pylori test, therapeutic trial; if this fails, endoscopy or UGI series

CT , Computed tomography; GI , gastrointestinal; IV , intravenous; MRCP , magnetic resonance cholangiopancreatography; MRI , magnetic resonance imaging; UGI , upper gastrointestinal; US , ultrasound.


The normal esophagus has a rather smooth lining. Two indentations, due to impressions by the aortic arch and the left main stem bronchus, can be seen along the left side ( Fig. 6.20 ). Normally, a peristaltic wave, initiated by swallowing, propels food down the esophagus. You should not diagnose a stricture on the basis of one image alone because you may be looking at a normal area of peristaltic contraction. Sometimes, in the distal portion of the esophagus, a Z line can be seen going across the esophagus. This represents the junction between the mucosa of the esophagus and the stomach ( Fig. 6.21 ).




Fig. 6.20


Normal Anatomy of the Esophagus.

The upper portion of the esophagus is seen in the image on the right and the lower half in the image on the left. An indentation along the left side of the esophagus occurs from the aorta (Ao) and another less significant one from the left main stem bronchus (LB) . As the distal aspect of the esophagus goes through the diaphragm, the gastroesophageal junction (GE , arrow) also can be identified.



Fig. 6.21


Junction of the Esophageal and Gastric Mucosa.

In the distal esophagus, it is sometimes possible to see a dark horizontal zigzag line (between the two arrows ). This is called the Z line and represents the normal junction between the two different types of mucosa.


Dysphagia and Odynophagia


Initially, it is important to differentiate dysphagia (difficulty swallowing or sticking of food) from odynophagia (pain with swallowing). The most common cause of dysphagia is a hiatal hernia with gastroesophageal reflux disease (GERD). Patients with mild dysphagia do not need imaging or endoscopy but they should have a trial of GERD medical therapy. Patients with severe symptoms should be investigated with endoscopy or barium swallow.


Many patients 60 to 80 years of age have dysmotility and do not pass food properly. They generally have vague symptoms. A barium swallow is indicated to exclude other pathology. Patients who complain of food getting stuck often have a benign or malignant stricture. These usually require endoscopy with biopsy.


Difficulty swallowing can also be the result of central nervous system pathology. Pharyngeal paresis with ineffective constriction of muscles may be due to abnormalities involving cranial nerves IX and X, stroke, or degenerative changes. In these patients, failure to close the glottis often results in aspiration.


Odynophagia is usually due to an infection or medication that produces esophagitis. In these patients, a barium swallow can visualize ulcerations or other characteristic mucosal patterns (such as herpes). Endoscopy also can be used, with the advantage of a biopsy of visualized abnormalities.


Esophageal Diverticula


In the lower cervical region, sometimes a pharyngeal diverticulum (Zenker diverticulum) projects posteriorly. Food can be caught in this, causing dysphagia ( Fig. 6.22 ). In the middle of the esophagus (near the carina), a traction diverticulum may be caused by scarring from mediastinal granulomatous disease. Just above the stomach, a pulsion diverticulum can sometimes be found. The two latter types are rarely symptomatic.




Fig. 6.22


Zenker Diverticulum.

This is basically an outpouching of mucosa (ZD, arrow) in the pharynx. Food can be caught in this and cause symptoms. The esophagus (E) can be seen distally.


Presbyesophagus


As a function of aging, tertiary deep contractions may develop within the esophagus. These are usually disordered and can interfere with the normal peristaltic process and swallowing. These tertiary contractions are easily visualized as multiple transverse or ringlike contractions of the esophagus ( Fig. 6.23 ). No specific therapy is indicated for this condition, and it is common in persons older than 60 years.




Fig. 6.23


Presbyesophagus.

These tertiary or ringlike contractions (arrows) are commonly seen in older persons, and they can disrupt the normal peristaltic motility of the esophagus.

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Feb 19, 2020 | Posted by in GENERAL RADIOLOGY | Comments Off on Gastrointestinal System
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