In the previous post we reviewed the contrast indications for CT of the abdomen and CT of the abdomen and pelvis. Most CT scans are performed with contrast, while a few CT scans are best performed without contrast. In this post I will describe those clinical circumstances in which multi-phase studies (dual and triple scans) are indicated.
Solid organ lesions are often discovered as incidental findings when performing another imaging study. For example, a CT chest for lung cancer screening, which will view the top of the kidneys and liver., may show an incidental lesion. Other times an ultrasound of the abdomen, performed for suspected cholecystitis, will find an unexpected lesion in the kidney or liver. The incidental solid organ lesion will then require additional imaging to characterize it as either benign or malignant. Contrast is important in many of these evaluations to make the correct diagnosis, but the imaging study requested is often multiple phasic contrast study and must be very specific.
When a mass or lesion is discovered in an abdominal organ (kidney, liver, pancreas or spleen) by a chest CT, a repeat CT dedicated to the abdomen is indicated. The most common follow up scan will be a CT abdomen without and with contrast (74170). If these scans cannot differentiate between a benign lesion or a malignant one, an MRI abdomen may be indicated. Alternatively, if the lesion’s suspicion for malignancy is low, follow up CT scan in a few months is another option.
Dual abdominal CT scans (without and with contrast – 74170) are also helpful to diagnose gall bladder polyps, pancreatic pseudocysts, pancreatitis, evaluation of jaundice, and in patients with cirrhosis and portal hypertension when considering surgical or radiological interventions.
Occasionally an abdominal mass cannot easily be diagnosed with a dual contrast CT, and additional imaging views are required. One such study is called a triple phase CT abdomen with washout. Delayed views are obtained and the percent of contrast washed out is calculated. This is also a key imaging study in the evaluation of adrenal cortical lesions that are not considered benign by density calculation on a non-contrast CT abdomen.
Some liver lesions are not readily diagnosed with a simple CT with contrast (74160) or dual study (CT without and with contrast 74170) and additional imaging is required. Liver lesions, for example, may require a multi-phase CT scan using
• 1st Non-contrast phase
• then Arterial phase
• then Portal venous phase
• finally a Delayed washout phase
Despite the 4 imaging views, CTs abdomen with multi-phase views are still coded as a dual study CT (74178)
Liver hemangiomas usually demonstrate specific fat and calcium content seen on CT abdomen without and with contrast. If classic features of hemangioma are not seen, delayed views with washout may be required to confirm the diagnosis. Suspected focal nodular hyperplasia is another of a liver finding that may require delayed multiphase contrast CT scan.
Patients with hematuria may require a high-radiation, high-contrast imaging study called a CT Urogram. This begins with CT abdomen and pelvis without contrast, followed by a post injection phase (also called the nephrogram phase). A third early wash-out phase is then used to demonstrate filling of the proximal collecting system, and a delayed washout phase to exclude obstruction. The final phase of this study is to follow the contrast into the filled bladder and distal ureters. At the discreation of the radiologist, additional thin slices can be requested to enhance visualization of the kidneys and the renal lesion. Regardless of how many phases are imaged and how many thin sections are viewed, the CPT code is usually the same for dual and triple studies – 74170 for CT abdomen and 74178 for CT abdomen and pelvis.
Lesson #20: When a lesion is discovered in an abdominal organ, additional imaging is usually required to determine the nature of the lesion. Although this often requires only a CT dual study (without and with contrast 74160 for abdomen and 74178 for abdomen plus pelvis) but occasionally a multiple contrast study with additional washout views are required. Consulting with a radiologist to communicate your suspicions, and referring to established guidelines will enable you to request the best CT imaging study for your patient. This not only will minimize over-radiation and follow evidence-based specialty guidelines but will allow you to obtain quick approval for the requested imaging study and avoid peer-to-peer calls.