Is a CT scan always necessary? A retrospective study looking at the diagnostic utility of US, CT and MRI imaging for liver lesions. Karthik Penumetsa, M.D., Matthew Weed, M.D., Uma Sundaram, M.D. Section of Digestive Diseases, Department of Internal Medicine and West Virginia Clinical and Translational Science Institute West Virginia University, Morgantown, WV.

BACKGROUND  To investigate suspected liver lesions, ultrasound (US) is routinely used as the initial imaging modality.  Subsequent use of computed tomography (CT) often followed by magnetic resonance imaging (MRI), which is currently regarded as the most confirmatory imaging test, is common in clinical practice for further diagnosis of liver lesions.  However, the diagnostic utility of both routine CT and MRI to confirm these US findings still remains unclear.

HYPOTHESIS CT scan may not yield any additional information to US or MRI findings of liver lesions. AIM To determine the added diagnostic utility of CT scan for hepatic lesions initially detected by ultrasound.

METHODS  This retrospective study was granted exempt status by WVU institutional review board. It included all adults receiving an abdominal US, CT and MRI from January 2003 to October 2009 at WVU hospital for suspected liver lesions.  288 patients were identified who had all three (US, CT and MRI) imaging modalities performed.  Lesions were classified as malignant ( Hepatocellular carcinoma or metastasis) or non-malignant ( Cyst, focal nodular hyperplasia, hemangioma or negative finding s ) based on final MRI results.

RESULTS  Of the 288 patients, 245 non-malignant and 43 malignant lesions were identified on MRI.  In detecting non-malignant lesions, US was accurate 94% of the time and CT was correct 98%, as confirmed by MRI.  In the detection of malignant lesions, neither US nor CT were superior to one another as both were 33% accurate as determined by MRI.

RESULTS ( Detection ratios (%) of liver lesions when US and CT were compared to MRI ) In the 10 malignant lesions missed by US, there was presence of ascites at the time of imaging. In patients without ascites when US was negative, 0 of 159 patients had malignancy on MRI. Indeterminate or non-diagnostic lesions detected on US and CT were similar (30% each). Of these non-diagnostic lesions, MRI was diagnostic for malignant lesions in 25% for US and 30% for CT.

Comparision of the ability to detect malignant vs non-malignant lesions using all three imaging modalities. (Estimated proportion=0, Confidence Interval of 95%: )

CONCLUSION  CT does not appear to improve the diagnostic yield of non- malignant, malignant or indeterminate lesions when first detected by US.  If US imaging is normal but clinical suspicion remains high (e.g presence of ascities), MRI may be the next step in imaging.  Larger, multicenter studies are necessary to confirm potential cost savings and minimize systemic risks associated with CT contrast agents.

THANK YOU  References:  Nimer Assy, Gattas Nasser, Agness Dijibre, Zaza Beniashvilli, Saad Elias and Jamal Zidan. Characteristics of common solid liver lesions and recommendations for diagnostic workup. World J gastroenterol July 14; 15 (26):  Filipe Caserio- ALVES. How to charcterize the incidental liver lesion. Faculty of medicine, University of Coimbra, Portugal.  Milijenko Marotti, Ratimira Klaric – Custovic, Ivan Krolo, Nenad Babic. Magnetic resonance imaging of liver lesions. Act din Croat 2002; 41 (suppl):  Special thanks: - Gerry Hobbs. PhD. (Biostatician)