Gastrointestinal Radiology

The evolution of fiberoptic endoscopy has brought about a profound change in the frequency and spectrum of examinations performed by abdominal radiologists today. No other subspecialty in radiology has undergone a comparable shift in recent decades. Direct visualization of the gastrointestinal tract has largely replaced classical radiology, especially in the evaluation of the stomach, duodenum, and colon. While our forefathers (look for some gray-haired survivors in the dark corners of the department) performed dozens of upper GI examinations per day, today's students and residents have little chance to witness a significant number of these skillful examinations during their rotations in GI radiology. On the other hand, their odds of seeing a double contrast barium enema are much higher. While the resulting images are quite appealing visually when obtained by a real master of this dying art, their diagnostic yield is typically inferior to that of endoscopy.

f The endoscopic studies of the stomach, the duodenum, ¿ and the colon are unsurpassed because they permit direct visualization of the mucosal surface and allow for immediate tissue sampling of suspicious findings or even interventions such as stent placement during the same session.

One thing applies to both endoscopy and barium studies: quality and efficiency rely heavily on the operator. As always, radiologists are somewhat more exposed than other specialists: a rotten barium study can haunt a radiologist for ages.

The classical radiological imaging methods such as upper GI examination still play an important role whenever physiological motion plays a role (swallowing, peristalsis of the esophagus, gastric motility, etc.) and in postoperative patients, e.g., when the evaluation of an anastomosis has been requested. The oral administration of contrast is obligatory in these cases. For intestinal segments that are inaccessible for the normal endoscope—in particular the mid to distal small bowel—radiological procedures remain a diagnostic mainstay. Capsule endoscopy is an emerging direct, nonionizing modality that uses a small radiofrequency transducer that is swallowed and acts as a camera imaging the small bowel; this might turn the tide in the near future.

Sectional imaging techniques such as ultrasound, CT, and MRI are increasingly gaining ground in the radiological evaluation of the hollow viscera: virtual coloscopy is just one example (Fig. 9.1a, b). On the other hand, contrast-enhanced sectional imaging undoubtedly is the gold standard of the radiological evaluation of the solid organs in the abdomen.

I Virtual Colonoscopy

I Virtual Colonoscopy

Virtual Colonoscopy

Fig. 9.1a What you see here is an endoscopy-type image reconstructed from spiral CT sections. Asmall polyp on a long stalk is clearly seen hanging from the roof of this colonic segment. b Modern imaging can do what pathologists do when they examine an intestine macroscopically: The intestine is cut open along its longitudinal axis and unfolded to check the interior for abnormalities. There is a drawback, though: The bowel must be absolutely clean and that depends wholly on patient compliance.

Fig. 9.1a What you see here is an endoscopy-type image reconstructed from spiral CT sections. Asmall polyp on a long stalk is clearly seen hanging from the roof of this colonic segment. b Modern imaging can do what pathologists do when they examine an intestine macroscopically: The intestine is cut open along its longitudinal axis and unfolded to check the interior for abnormalities. There is a drawback, though: The bowel must be absolutely clean and that depends wholly on patient compliance.

Suggestions for diagnostic modalities in gastrointestinal imaging

Tabie 9.1 Suggestions for diagnostic modalities in gastrointestinal imaging1

Clinical problem

Investigation

Comment

Acute abdomen

Acute abdominal pain (warranting hospital admission and surgical consideration); perforation; obstruction

AXR erect and CXR erect, US

Erect or left-side-down AXR with horizontal beam indicated routinely for gas pattern and free air. US for free fluid.

CT

To further classify findings.

Palpable mass

US

Often solves the problem.

CT

Where US is inconclusive.

Acute GI bleeding: hematemesis

Endoscopy

Provides diagnosis of upper GI lesions; allows injection of varices, etc.

US

Only useful to look for signs of chronic liver disease.

Angiography

In uncontrollable bleeding. Can accurately direct surgery and transcatheter embolization; may be used as primary treatment

NM (red cell study) After endoscopy. Can detect bleeding rates as low as 0.1 mL/min;

more sensitive than angiography. Red cell study is most useful in intermittent bleeding.

Diseases of the esophagus and stomach

Difficulty in swallowing

Barium swallow

Barium studies are still recommended before possible endoscopy; will accurately localize lesions and show the degree of obstruction caused by a stricture and its length. Webs and pouches are well demonstrated. Subtle strictures may be demonstrated by a marshmallow (or other bolus) study. Detailed fluoroscopy or NM needed for motility disorders.

Video fluoroscopy

For suspected pharyngeal dysfunction in conjunction with speech therapists.

Chest pain

?Hiatus hernia or reflux

Endoscopy

Best for metaplasia and esophagitis because it also allows biopsy.

pH monitoring

Generally regarded as the "gold standard" to diagnose acid reflux but gives no anatomical information.

Barium swallow/meal

Although useful to demonstrate hernia, reflux, and their complications, not all such patients need a work-up. Reflux is common and not necessarily the cause of pain. NM may be oversensitive. Increasing use of barium studies before antireflux surgery.

Esophageal perforation

CXR

Will be abnormal in 80%; pneumomediastinum will show in 60%. May be sufficient, unless localization for surgical repair is planned.

Two schools of thought exist: (A) Study should be performed with water-soluble nonionic contrast agents. If no leak is seen, proceed immediately to CT. (B) Study should initially be performed with nonionic contrast agents. If no leak is seen, one should switch to barium for better detail.

CT

Sensitive for presence of perforation and mediastinal and pleural complications.

AXR, abdominal radiograph; CT; computed tomography; CXR, chest radiograph; ERCP, endoscopic retrograde cholangiopancreatography; GI, gastrointestinal; HIDA, hepatobiliary imino-diacetic acid; MRCP, magnetic resonance cholangiopancreatography; MRI, magnetic resonance imaging; NM, nuclear medicine; US, ultrasound; WBC, white blood cell.

Table 9.1 Suggestions for diagnostic modalities in gastrointestinal imaging1 (Continued)

Clinical problem

Investigation

Comment

Dyspepsia in the younger patient (e.g., under 45 years)

Imaging

(endoscopy/barium meal)

Most patients under 45 years can be treated without complex investigations and will undergo a trial of therapy to lower gastric acidity. Endoscopy, or alternatively barium meal, for those who fail to respond. Other alarming features pointing to early investigation include unintentional weight loss, anemia, anorexia, GI bleeding, pain requiring hospitalization, nonsteroidal antiinflammatory drugs, vomiting, no improvement following treatment in those positive for Helicobacter pylori.

Dyspepsia in the older patient (e.g., over 45 years)

Imaging (barium meal/endoscopy)

Endoscopy is the modality of choice. The main concern is the detection of early cancer, especially submucosal tumors. If endoscopy is negative and symptoms persist, then barium meal should be considered.

Ulcer follow-up

Endoscopy

Preferred to confirm complete healing and to obtain biopsies (e.g., Helicobacter pylori) where necessary.

Barium studies

Not indicated. Scarring precludes accurate assessment.

Carbon-14 breath test

To assess effect of treatment of Helicobacter pylori.

Diseases of the small bowel

Small-bowel obstruction

AXR

Indicated for primary diagnosis.

Contrast studies

With nonionic agents can determine both the site and completeness of obstruction.

CT

Some centers use CT in this situation, which can determine level and likely cause.

Small-bowel obstruction: chronic or recurrent

Small-bowel barium enema

Examination of choice; will reveal presence and level of obstruction in most cases; may suggest cause.

Small-bowel disease suspected (e.g., Crohn disease)

Small-bowel barium enema or follow-through

Investigation of choice to establish extent of disease prior to surgery, any fistula, cause of obstruction. Some centers use US to assess bowel wall.

NM (white cell study)

Labeled white cell scintigraphy may reveal activity and extent of disease. Complementary to barium studies.

MR

Increasing use as modality for extramural extent and to keep radiation dose low.

CT

Reserved for complications.

Malabsorption

Barium small-bowel follow-through

Imaging is not required for the diagnosis of celiac disease but may be indicated for jejunal diverticulosis or when biopsy is normal/equivocal.

Diseases of the large bowel

Large-bowel tumor or inflammatory Barium enema Colonoscopy is often first-line investigation. Air-contrast enema bowel disease: pain, bleeding, is useful if the bowel is properly prepared. Furthermore, all change in bowel habit, etc. patients should undergo rectal examination to assess suitability for barium enema and to exclude a low rectal tumor. Good practice requires a sigmoidoscopy before barium enema. Defer barium enema for 7 days after full-thickness biopsy via a rigid sigmoidoscope. Biopsies taken during flexible sigmoidoscopy are usually superficial and require no delay of enema.

AXR, abdominal radiograph; CT; computed tomography; CXR, chest radiograph; ERCP, endoscopic retrograde cholangiopancreatography; GI, gastrointestinal; HIDA, hepatobiliary imino-diacetic acid; MRCP, magnetic resonance cholangiopancreatography; MRI, magnetic resonance imaging; NM, nuclear medicine;US, ultrasound; WBC, white blood cell.

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