Imaging Strategies

Author:  Charles Allison, MB ChB

Editor: Ashley Davidoff MD

The Common Vein Copyright 2006

BACKGROUND: 

Epigastric pain is usually attributable to foregut structures (including the esophagus, stomach, duodenum and pancreas). Liver pathologies, though derived from the foregut, typically present as RUQ pain. Possible etiologies of epigastric pain include:

Esophagitis

Gastritis, gastric ulcer

Duodenitis, duodenal ulcer

Pancreatitis

Choice of imaging clearly hinges on the suspected diagnosis. Pain eased by or worsened by food is more likely to represent peptic ulcer disease (duodenal and gastric, respectively). Acute, severe epigastric pain raises the possibility of a perforated duodenal ulcer. A history of gallstones or heavy alcohol use may suggest pancreatitis. The majority of patients will not require any imaging at all.

WHAT STUDY?

Most patients will not be imaged. Endoscopy, CXR or CT are the modalities most likely to be required in patients with worrying symptoms.

Upright chest radiographs can be used to exclude free air under the diaphragm if a perforated ulcer is suspected (severe, sudden onset of pain; peritonism on examination)

EGD (esophagogastroduodenography) is the investigation of choice in suspected peptic ulcer disease. Associated hematemesis would prompt urgent endoscopy, whereas lesser symptoms more suggestive of gastritis and without evidence of H. pylori infection may initially be treated empirically with lifestyle changes and acid suppression. Chronicity of such epigastric pain may be an indication for endoscopy to exclude ulcers and to biopsy for H. pylori.

CT abdomen is the investigation of choice for suspected pancreatitis. Oral contrast (gastrograffin) and intravenous contrast should be used if possible. Mucosal lesions in the upper GI tract such as gastritis or ulcers may be missed. It also involves a relatively large dose of radiation; approximately 500 times that of a plain chest radiograph, the equivalent of about 3.3 years of normal background radiation.

MRI provides excellent cross sectional imaging, providing superior images of the soft tissues and organs. It is non invasive but expensive and may be more geographically limited than CT. It also takes much more scanning time in somewhat claustrophobic conditions hence some patients are not able to tolerate the procedure.

WHY?

Upright chest radiographs cause any peritoneal free air to collect as an abnormal lucency under the diaphragm; allowing radiological diagnosis in around 70% of cases of perforation. Free air may also be seen on plain abdominal films, but is more easily missed.

EGD is the investigation of choice in suspected peptic ulcer disease. It directly visualizes the esophagus, stomach and duodenum and can thus aid diagnosis of esophagitis, hiatus hernia, gastritis, peptic ulcers and gastric carcinoma. It has the added benefit of allowing biopsies to be taken in suspicious masses or ulcers and can be used therapeutically if there is bleeding.

CT scanning is very fast and provides information on a wide spectrum of pancreatic and gastrointestinal pathologies. It provides information of the severity of pancreatitis and may also detect predisposing factors such as gallstones or dilated common bile ducts.

MRI provides equivalent diagnostic accuracy to CT in most pathologies. Though it does not carry the radiation burden of CT, it is more expensive, time consuming and may be more geographically limited and less acceptable to the patient. These factors make it less used than CT as a diagnostic modality in acute pain.

WHEN?

Imaging should be performed at time of presentation if the patient is in acute pain to expedite diagnosis / management.

HOW TO ORDER?

It is important to reference the symptom or the sign as the clinical indication and not the diagnosis.

ie Patient with “epigastric pain” is acceptable, whereas R/O pancreatitis is not acceptable.  

Optimal ordering would list symptoms/signs as well as the putative diagnosis being investigated: “epigastric pain, fever, r/o pancreatitis”. This allows the radiologist to suggest alternative imaging strategies if a suboptimal approach has been ordered.

PATIENT PREPARATION

Plain radiography for an upright chest involves the patient standing with a plate in front of them and the radiation source behind for a standard PA view. They will be asked to take a deep breath in, and hold it for a second while the x-ray is taken. The entire procedure takes less than a minute.

EGD is typically performed by a gastroenterologist under waking sedation. Local anesthetic spray is use to numb the oropharynx and benzodiazepine sedation is administered prior to the procedure. The procedure itself usually takes under 30 minutes, though time is required after the procedure for the effects of sedation to wear off. Patients should not drive the same day of the procedure. The most common side effect is sore throat.

CT preparation depends on the use of contrast. For renal stones no contrast in required and the patient may be scanned immediately. Administration of oral contrast required drinking or NG administration of 30cc gastrograffin diluted in 900cc water to ensure it adequately coats the length of the bowel. Intravenous contrast in given in the scanner and may be timed to highlight the arterial or venous supply to a specific organ. The patient’s allergies, medications and renal function need to be identified before hand as the contrast is iodine based and carried risk of precipitating renal failure in at risk patients (diabetic, on metformin etc). The study itself takes about 1 minute once the patient is on the table

Patients undergoing MRI should be warned that they will be required to lie still in a confined tunnel-like space for up to 30 minutes. The machine is very noisy and ear protection will be provided. They will have a call button to abort the procedure if a problem should arise.

CLINICAL RED FLAGS:

Tachycardia, peritonism and history of duodenal ulcer may suggest perforation, a surgical emergency. This diagnosis can be rapidly supported with an upright CXR.

Fever, severe epigastric pain radiating to the back and a history of gallstones or alcohol abuse are suggestive of acute pancreatitis, the gold standard test for diagnosis is CT abdomen with contrast, though if suspected aggressive fluid resuscitation should be started even before imaging.

REFERENCES:

What are the radiation risks from CT? – US Food and Drugs Administration

http://www.fda.gov/cdrh/ct/risks.html