Flank Pain. CT with or without contrast?

Hx: A middle aged man presents with flank pain. He has no past medical history and notes sudden onset of severe, sharp, left flank pain. He denies any history of similar symptoms. Pain is constant, and does not radiate. No associated chest pain, shortness of breath, or abdominal pain. No hematuria, dysuria, hx of kidney stones, change in stools, or blood in the stool. No fever.


  • Vitals: HR 100, BP 170/90, sat 100% room air, RR 18
  • General: appears to be in significant pain and cannot find a position of comfort.
  • HEENT: normal
  • Resp: tachypneic, clear to auscultation bilaterally, no wheezes.
  • Cardiovascular: tachycardia, regular, no murmurs, pulses normal all extremities
  • Abdomen: soft, non-tender,
  • Extremities: warm, normal sensation
  • Back: pain in left flank without change with movement or palpation.

ED Course:

  • Initial differential focused on renal pathology with renal colic at the top of the list.
    • kidney / ureteral  stones
    • pyelonephritis
    • renal infract / embolism
  • The patient is given narcotic pain medication and blood and urine is obtained.
  • Labs are unremarkable and urine is clear.
  • A CT urogram is obtained and shows:
CT urogram, Flank Pain, Kidneys
Normal Kidneys
Image courtesy of Sam Ashoo, MD
CT urogram, Flank Pain, Upper Abdomen
Unremarkable Upper Abdomen
Image courtesy of Sam Ashoo, MD
CT urogram, Normal Kidney, Flank Pain
Normal Kidneys Without Stones or Hydronephrosis
Image courtesy of Sam Ashoo, MD
  • On repeat examination the patient has received little relief with multiple doses of pain medication and has no cause for the severe pain found on CT. The patient has no history of prior visits, narcotic pain medication prescriptions or opiate tolerance, and is still in severe pain. The differential is expanded to include left lower lobe pulmonary embolism and a D-Dimer is ordered.
  • The d-dimer returns markedly elevated.
  • A CT pulmonary angiogram is ordered and results in the images below:
CT pulmonary angiogram
The top of a descending aortic dissection is seen at the aortic arch, next to the vertebral body.
Image courtesy of Sam Ashoo, MD

Diagnosis: Acute Descending (Type B) Aortic Dissection

CT pulmonary angiogram, aorta, Flank Pain
A comparison of the sub-diaphragmatic aorta seen on the contrast study (left) where the dissection can be seen, and the same area without contrast (right) where the aorta appears normal.
Image courtesy of Sam Ashoo, MD


With or without contrast? A decision that we make routinely when obtaining imaging by computed tomography (CT). As CT technology has improved, numerous studies have been published regarding the decreasing need for enteric or IV contrast in the emergency setting when imaging the abdomen. These high resolution (64 slice or higher) CT studies are capable of differentiating tissue planes when an adequate amount of intra-abdominal fat is present. This allows for visualization of “infiltration of fat” or edema of the fat surrounding structures like the colon, small bowel, appendix, and retroperitoneal structures like the kidney. The edema becomes a substitute for the hyperemia seen when IV contrast is given and becomes a surrogate marker for inflammation pointing to a pathologic finding. However, even this advanced technology has its limitations.

At a time when many departments forgo the administration of contrast in order to facilitate patient flow, it is important to remember the limitations of the non-contrast study.

This case highlights several key issues:

  1. The differential diagnosis: The patient’s presentation appeared classic for renal colic and he had no risk factors for other disease. The differential was short but did not initially include aortic dissection. Even the expanded secondary differential did not include it. Flank pain can be caused by dissection especially when it involves the renal artery. However, this case highlights the possibility of referred pain from dissection of the aorta presenting as flank pain, even in the absence of renal artery involvement. Though atypical, it should be included in the initial differential. This does not mean it must be excluded by diagnostic testing, but it should be considered.
  2. The repeat examination: The physician caring for this patient performed one of the most important steps when caring for a patient, the repeat examination. When items on the differential diagnosis have been excluded and no diagnosis has been found, a repeat exam and interview is often helpful. This type of “reset” allows for expansion of a differential, additional historical items to be obtained, and for discovery of new or evolving physical exam findings. Whenever a patient’s response to treatment does not follow the anticipated coarse, or diagnostic testing does not result in an expected diagnosis (both in this case), it is critical to take time to re-evaluate the presentation and overcome any cognitive errors (like early closure).
  3. The benefit of contrast: Though CT imaging has come a long way, the identification of vascular abnormalities continues to require the administration of intravenous contrast. As this case highlights, non-contrast imaging of the aorta relies on edema of surrounding structures or aneurysmal dilatation of the aorta to suggest abnormality. In the absence of either of these findings, no further analysis of the aorta can be made. The addition of contrast clearly highlights the intra-vascular space allowing for the correct diagnosis of this life threatening disease.

What do we take away from this case?

  • If the differential includes a vascular diagnosis (thrombosis, dissection, embolism) as a likely process, be sure to include the intravenous contrast.
  • Be careful not to dismiss the lack of response to treatment.
  • Re-examine the patient with a clear mind and a specific focus on expanding your differential if initial testing does not reveal your expected diagnosis and/or treatment is unsuccessful.

For Further Reading

Thoracic Aortic Syndromes in The Emergency Department: Recognition and Management

Acute aortic syndromes—aortic dissection, intramural hematoma, and penetrating atherosclerotic ulcer—are life-threatening conditions that demand swift recognition and treatment in the ED. This issue presents the latest evidence on managing AAS. Includes 4 AMA PRA Category 1 Credits™. CME expires on 12/01/2024

Imaging In The Adult Patient With Nontraumatic Abdominal Pain

Anyone who works in an emergency department (ED) knows that abdominal pain (or some variation of it) is one of the most frequent presenting complaints evaluated. Although it is difficult to truly quantify, it is estimated that abdominal pain accounts for 5 – 10% of all ED visits and that emergency physicians care for nearly eight million patients with abdominal pain each year.1-3 The sheer volume of potential diagnoses coupled with the lack of evidenced-based standards create a dilemma when determining a diagnostic study choice. The question of which radiological modality and when to utilize it is further complicated by the rapid advances in radiolographic technology. The goal of this Emergency Medicine Practice article is to provide a functional framework for the diagnostic evaluation of the patient with nontraumatic abdominal pain.

Last Updated on January 24, 2023

11 thoughts on “Flank Pain. CT with or without contrast?

  1. The use of POCUS could help in this case – our department protocol says that if there’s no hydronephrosis on US – use contrast CT for flank/abdominal pain

  2. In Flank pain use of pocus combi ed with a Negative Ddimer normally rule out acute partic disease and if hydronephrosis is detected an aneurisma can Be escludesse only by po cus. What do you think about this approaxh?

    1. Thanks Sibilla. You have to be careful trying to exclude dissection by ultrasound. An aneurysm can be visualized by ultrasound but, as this case reveals, a dissection can be missed even by ct without contrast. Also, the D dimer is not sufficient to exclude a dissection. Certainly the lack of hydronephrosis would increase the likelihood of dissection on the differential.

  3. Nice case! But this is hardly the “same” location on the comparison diagram between CTKUB and aortogram. The CTKUB conveniently missed out showing the aorta just under the diaphragm. I want to know how that aorta looked like on the non-contrast KUB scan. I bet it was noticeable.

    1. You are correct, the images are not the same cut/level. But unfortunately I don’t have the original studies to give you the exact cuts. Regardless, the non-contrast study was not enough for the reading radiologist to notice anything.

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