| RLQ pain
Imaging Strategies Author: Charles Allison, MB ChB Editor: Ashley Davidoff MD The Common Vein Copyright 2006 BACKGROUND: The differential of right lower quadrant pain includes gastrointestinal, genitourinary and gynecologic diagnoses. Some possible etiologies of RLQ include: Acute appendicitis Mesenteric adenitis Inflamed Meckel’s Diverticulum Crohn’s disease Infectious ileitis Perforated cecal carcinoma
Renal colic Urinary tract infection
Torsion of ovarian cyst Salpingitis Ectopic pregnancy Choice of imaging clearly hinges on the suspected diagnosis. WHAT STUDY? CT or ultrasound are the modalities most likely to be required. CT is the investigation of choice in most cases, with the exception of children under 14 and pregnant women, in whom ultrasound is preferred. Oral contrast should be administered. Intravenous contrast is preferred but need not be given if there is a contraindication. CT has a higher sensitivity and specificity for appendicitis than ultrasound (94 and 95% respectively for CT, compared 84% and 81% for ultrasound). CT is superior in imaging appendiceal abscess and also more likely to pick up non-appendiceal causes of RLQ pain than ultrasound. It does however involve a relatively large dose of radiation. Ultrasound is the investigation of choice in pregnant patients and children under 14. Graded compression abdominal ultrasound is preferred for RLQ characteristic of appendicitis, in pregnancy and in children. In other cases with a wider differential, there is no preference between abdominal and endovaginal imaging. Ultrasound has a higher sensitivity and specificity for detecting appendicitis in children due to smaller body habitus – around 91% and 97% respectively. Ultrasound is relatively inexpensive and non-invasive but there is some heterogeneity in sensitivity related to operator skill. MRI may be used as an alternative to ultrasound in pregnant patients with RLQ pain, fever and leucocytosis. It provides excellent cross sectional imaging, providing superior images of the soft tissues and organs. It is less well validated in the diagnosis of appendicitis and less sensitive than CT for renal stones. WHY? CT scanning is very fast and provides information on the full spectrum of bowel, genitourinary and gynecological pathologies. CT is superior in imaging appendiceal abscess and also more likely to pick up non-appendiceal causes of RLQ pain than ultrasound. It does however involve a relatively large dose of radiation. Oral contrast is important to highlight the bowel mucosa and should always be given in abdominal CT imaging when possible. Intravenous contrast in not necessary for identifying appendicitis but may aid diagnosis of other pathology. Ultrasound is relatively inexpensive and non-invasive but may be somewhat operator dependent. It is slightly less good than CT for detecting appendicitis, but excellent for imaging gynecological pathology, particularly via the endovaginal route when the probe is in close proximity to the Fallopian tubes and ovaries. Abdominal ultrasound may be limited by patient factors such as excessive size or presence of bowel gas obscuring the image. MRI has less data to support its use than CT in RLQ pain, though small case series have supported its utility in appendicitis. It may be considered in cases when CT is less desirable, such as pregnancy. 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. It takes much more scanning time in somewhat claustrophobic conditions hence some patients are not able to tolerate the procedure. These factors make it less used than CT as a diagnostic modality in RLQ. Plain abdominal radiographs will not add useful information to CT in the setting of RLQ pain. Appendicitis will be not evident though there may be a suggestive fecolith. It may be possible to see renal stones (90% radio opaque), most commonly at the pelvocalyceal junction, as the ureter crosses the pelvic brim or at the trigone as the ureter enters the bladder. However, not all radio-opaque stones are visible on KUB. Small bowel follow through or barium enema can be used to evaluate for small bowel obstruction, ileitis (as in yersinia infection) and inflammatory bowel disease. They are rarely used in the acute setting, when CT imaging is preferred. Tagged WBC nuclear scanning has been used for RLQ pain, but is not recommended in the acute setting. It may help in confirming the presence of inflammation but lacks specificity. 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 “RLQ pain” is acceptable, whereas R/O appendicitis is not acceptable. Optimal ordering would list symptoms/signs as well as the putative diagnosis being investigated: “RLQ pain, fever r/o appendicitis”. This allows the radiologist to suggest alternative imaging strategies if a suboptimal approach has been ordered. PATIENT PREPARATION The patient should be fasting for 4 hours before an ultrasound examination; the procedure takes about 30 minutes. 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 problem arises. CLINICAL RED FLAGS:
Acute onset of severe right or left lower quadrant pain in a hypotensive young female should prompt an urgent abdominal and/or endovaginal ultrasound to exclude ruptured ectopic pregnancy.
REFERENCES:
ACR Appropriateness Criteria http://www.acr.org/s_acr/bin.asp?CID=1207&DID=11763&DOC=FILE.PDF
Family Practice Notebook http://www.fpnotebook.com/about.htm
Lecture Notes on General Surgery – Ellis H, Calne R, Watson C Blackwell Science 2001
Acute appendicitis: MR imaging and sonographic correlation – Incesu L, Coskun A, Selcuk MB AJR 1997; 168(3): 669-74 |