Imaging Strategies

Author:  Charles Allison, MB ChB

Editor: Ashley Davidoff MD

The Common Vein Copyright 2006

BACKGROUND: 

The differential diagnosis of left upper quadrant pain is wide. Anatomically, the culprit organ systems should include spleen, tail of pancreas, and splenic flexure of colon. Nociception from foregut structures (including the stomach and pancreas) typically present in the epigastric region but may sometimes localize to the LUQ. Possible etiologies of LUQ include:

Splenic infarct, splenic rupture, splenic abscess

Pancreatitis

Renal colic, pyelonephritis, renal infarction

Left lower lobe pneumonia

Herpes zoster

Choice of imaging clearly hinges on the suspected diagnosis.

WHAT STUDY?   CT and MR are the modalities most likely to be required.

CT is perhaps the investigation of choice when the differential cannot be narrowed. It is preferred over ultrasound for renal colic or pyelonephritis as it has a higher sensitivity and specificity (>90%) for detecting stones. Oral contrast (gastrograffin) is always preferred if practical. Intravenous contrast should be omitted when looking for renal stones, but otherwise is required, aiding diagnosis of wedge shaped visceral infarcts or enhancing abscesses. Computed tomography is fast and provides information on the full spectrum of spleen, pancreatic and bowel pathologies as well as catching the bases of the lungs and hence possible pneumonias as the cause of the pain. It does however involve 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.

Some diagnoses are not aided by imaging, such as herpes zoster.

WHY?

Plain abdominal radiographs are rarely helpful in the setting of LUQ pain. It may be possible to see renal stones (90% radioopaque), most commonly at the pelvocalcyceal junction, as the ureter crosses the pevic brim or at the trigone as the ureter enters the bladder. However, not all radio-opaque stones are visible on KUB. Intravenous urography (IVU) was previously performed, looking for delayed excretion of hydroureter, but the procedure may take a number of hours, and has now been supplanted by CT (without intravenous contrast) when renal stones are suspected.

Ultrasound is not preferred over CT in LUQ pain. Though it may detect splenic abscesses, pleural effusions associated with pneumonia and renal pathologies, it is less sensitive than CT in making the diagnosis.

CT scanning is very fast and provides information on the full spectrum of liver, pancreatic and bowel pathologies as well as catching the bases of the lungs and hence possible pneumonias as the cause of the pain. It does however involve a relatively large dose of radiation. The administration of iv contrast may enhance some pathologies such as the outer ring of abscesses or the rich vascular supply of tumors. Gas within low attenuation liver lesions is pathognomonic of abscess.

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 LUQ 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 “LUQ pain” is acceptable, whereas R/O splenic infarct is not acceptable.  

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

PATIENT PREPARATION

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:

LUQ pain in the setting of recent blunt abdominal trauma raises the concern of splenic rupture. Tachycardia, generalized or localized guarding and dullness to percussion over the left flank support the diagnosis. Delayed onset of symptoms is not uncommon. Prompt CT scanning of the abdomen confirms the diagnosis and may detect other associated traumatic injuries and allows urgent surgical management.

REFERENCES:

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

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