MRI contrast enhancement of malignant liver tumours following successful cryoablation.

OBJECTIVES: To assess the incidence and degree of MRI contrast enhancement in liver tumours following successful percutaneous cryoablation. METHODS: Thirty-eight patients with liver metastases (n = 29) or hepatocellular carcinoma (n = 9) underwent percutaneous cryoablation of 45 tumours between March 2004 and June 2009, with complete ablation zone coverage of the tumour and no local recurrence on follow-up imaging to date (range 3-60 months, mean 16). Contrast-enhanced MRI was used to assess 45 tumours at 24 h, 32 tumours at 2-4 months, and 21 tumours at 5-7 months. Percentage of tumours with contrast enhancement was assessed using dynamic spoiled gradient echo T1-weighted images. RESULTS: Twenty-four hours post-cryoablation, 23 out of 45 tumours (51%) enhanced compared with 42 out of 43 (98%) pre-ablation (p < 0.001). Mean percentage tumour enhancement decreased from 157% (range 26-745%) pre-ablation, to 107% (27-260%) at 24 h (p = 0.003), and 43% (24-103%) at 2-4 months (p < 0.001). The incidence and degree of tumour enhancement decreased through 5-7 months. CONCLUSIONS: Unlike previously reported studies of radiofrequency ablation, successful cryoablation of liver tumours is often associated with persistent tumour contrast enhancement on MRI performed at 24 h and decreasing over 2-7 months. KEY POINTS: • Liver neoplasms often demonstrate MRI contrast enhancement following successful percutaneous cryoablation. • This differs from radiofrequency ablation techniques where contrast enhancement suggests residual tumour • This difference could potentially lead to important errors in follow up strategies.

Incidental finding of renal masses at unenhanced CT: prevalence and analysis of features for guiding management.

OBJECTIVE: The purposes of this study were to investigate the frequency and clinical relevance of the incidental finding of renal masses at low-dose unenhanced CT and to analyze the results for features that can be used to guide evaluation. MATERIALS AND METHODS: Images from unenhanced CT colonographic examinations of 3001 consecutively registered adults without symptoms (1667 women, 1334 men; mean age, 57 years) were retrospectively reviewed for the presence of cystic and solid renal masses 1 cm in diameter or larger. An index mass, that is, the most complex or concerning, in each patient was assessed for size, mean attenuation, and morphologic features. Masses containing fat or with attenuation less than 20 HU or greater than 70 HU were considered benign if they did not contain thickened walls or septations, three or more septations, mural nodules, or thick calcifications. Masses with attenuation between 20 and 70 HU or any of these features were considered indeterminate. The performance of CT colonography in the detection of renal cell carcinoma was calculated for masses with 2 or more years of follow-up. RESULTS: At least one renal mass was identified in 433 (14.4%) patients. The mean size of the index masses was 25 ± 16 mm; 376 (86.8%) masses were classified as benign and 57 (13.2%) as indeterminate. The 20- to 70-HU attenuation criterion alone was used for classification of 53 indeterminate lesions. Follow-up data (mean follow-up period, 4.4 years; range, 2-6.3 years) were available for 353 (81.5%) patients with masses (41 indeterminate, 312 benign). Four of the 41 indeterminate masses were diagnosed as renal cell carcinoma. The sensitivity and specificity for renal cell carcinoma on the basis of the indeterminate criteria were 100% and 89.4%. The positive and negative predictive values were 9.8% and 100%. CONCLUSION: The incidental finding of a renal mass is relatively common at unenhanced CT, but imaging criteria can be used for reliable identification of most of these lesions as benign without further workup. Mean attenuation alone appears reliable for determining which renal masses need further evaluation.

Renal cell carcinoma: t1 and t2 signal intensity characteristics of papillary and clear cell types correlated with pathology.

OBJECTIVE: The objective of our study was to describe the T1 and T2 signal intensity characteristics of papillary renal cell carcinoma (RCC) and clear cell RCC with pathologic correlation. MATERIALS AND METHODS: Of 539 RCCs, 49 tumors (21 papillary RCCs and 28 clear cell RCCs) in 45 patients were examined with MRI. Two radiologists retrospectively and independently assessed each tumor's T1 and T2 signal intensity qualitatively and quantitatively (i.e., the signal intensity [SI] ratio [tumor SI / renal cortex SI]). Of the 49 tumors, 37 (76%) were assessed for pathology features including tumor architecture and the presence of hemosiderin, ferritin, necrosis, and fibrosis. MRI findings and pathology features were correlated. Statistical methods included summary statistics and Wilcoxon's rank sum test for signal intensity, contingency tables for assessing reader agreement, concordance rate between the two readers with 95% CIs, and Fisher's exact test for independence, all stratified by RCC type. RESULTS: Papillary RCCs and clear cell RCCs had a similar appearance and signal intensity ratio on T1-weighted images. On T2-weighted images, most papillary RCCs were hypointense (reader 1, 13/21; reader 2, 14/21), with an average mean signal intensity ratio for both readers of 0.67 +/- 0.2, and none was hyperintense, whereas most clear cell RCCs were hyperintense (reader 1, 21/28; reader 2, 17/28), with an average mean signal intensity ratio for both readers of 1.41 +/- 0.4 (p < 0.05). A tumor T2 signal intensity ratio of < or = 0.66 had a specificity of 100% and sensitivity of 54% for papillary RCC. Most T2 hypointense tumors exhibited predominant papillary architecture; most T2 hyperintense tumors had a predominant nested architecture (p < 0.05). CONCLUSION: On T2-weighted images, most papillary RCCs are hypointense and clear cell RCCs, hyperintense. The T2 hypointense appearance of papillary RCCs correlated with a predominant papillary architecture at pathology.

Computed tomography features of nonalcoholic steatohepatitis with histopathologic correlation.

OBJECTIVE: This study was conducted to describe the computed tomography (CT) features of nonalcoholic steatohepatitis (NASH) and to evaluate if the CT features could be used to diagnose and stage NASH. METHODS: From 1994 until 2004, pathology records revealed 68 patients with NASH. Of these, 12 patients underwent CT scans before (n=6), on the same day as (n=3), or after (n=3) a liver biopsy. Using the same database, 9 patients with steatosis alone evaluated with a CT scan before (n=2), on the same day as (n=3), or after (n=4) the liver biopsy were selected as a control group. Two radiologists measured liver attenuation (compared with spleen) and assessed the pattern of steatosis, craniocaudal liver span, caudate-to-right lobe ratio, preportal space distance, and presence of porta hepatis lymph nodes and ascites. Biopsy specimens were assessed by a pathologist, and the degree of necroinflammatory activity, steatosis, and fibrosis was determined. Histopathologic and CT findings were compared between patients with NASH and patients with steatosis alone using the Mann-Whitney U test and Fisher exact test. RESULTS: In patients with NASH, the mean liver-to-spleen attenuation ratio was 0.66 (range: 0.1-1.1). Steatosis was diffuse (n=9), geographic or nonlobar (n=2), or diffuse with an area of focal sparing (n=1). The liver craniocaudal span varied from 17.5 to 25.5 cm (mean=21.4 cm), and hepatomegaly was present in 11 (91.7%) patients. The caudate-to-right-lobe ratio (mean=0.43) and preportal space (mean=4.5 mm) were normal in all cases. Porta hepatis lymph nodes were present in 7 (58.3%) patients; their mean dimensions were 16 mmx11 mm. Ascites was absent in all patients. On histopathology, the degree of necroinflammatory activity was mild (n=9), moderate (n=1), or severe (n=2). The degree of steatosis was 33% to 66% (n=5) or >67% (n=7). All but 3 patients had fibrosis; 6 had focal nonbridging fibrosis, 1 had multifocal nonbridging fibrosis, and 2 had bridging fibrosis. There was a significant correlation between the degree of steatosis on pathologic examination and the liver-to-spleen attenuation ratio on CT (P=0.048). The severity of inflammation and stage of fibrosis on pathologic examination did not correlate with the CT features. Among patients with steatosis alone, the mean liver-to-spleen attenuation ratio was 0.80 (range: 0.3-1.2); the craniocaudal liver span varied from 12 to 20 cm (mean=16 cm); hepatomegaly was present in 2 (22.2%) patients; the caudate-to-right lobe ratio was normal in all patients, with a mean of 0.36 (range: 0.22-0.47); the preportal space distance was enlarged in 2 cases (mean=7.5 mm, range: 1-16 mm); porta hepatis lymph nodes were present in 7 (77.8%) patients, and their mean dimensions were 11 mmx8 mm (large axis range: 6-19 mm, short axis range: 4-14 mm); and no patient had ascites. There was a significant difference in the craniocaudal liver span between patients with NASH (mean=21 cm) and patients with steatosis (mean=16 cm) (P<0.05). The caudate-to-right-lobe ratio was also significantly different between patients with NASH (mean=0.43) and patients with steatosis (mean=0.36) (P<0.05). There were no significant differences in liver-to-spleen attenuation ratios, measurements of preportal space, or the presence of porta hepatic lymph nodes. CONCLUSION: The CT features of NASH include steatosis, hepatomegaly, and porta hepatis lymph nodes, and the liver-to-spleen attenuation ratio correlated with the degree of steatosis on histopathology. Patients with NASH had a greater liver span and increased caudate-to-right-lobe-ratio compared with patients with steatosis alone.

State-of-the-art computed tomographic and magnetic resonance imaging of the gastrointestinal system.

Among the major innovations in radiology of the gastrointestinal (GI) system are the replacement of classic invasive diagnostic methods with noninvasive ones and the improvement in lesion characterization and staging of pancreatobiliary malignancies. Developments in imaging technology have led to many improvements in the field of diagnostic GI radiology. With its fast and thin-section scanning abilities, multidetector-row CT (MDCT) strengthens the place of CT as the most efficient tool to diagnose, characterize, and preoperatively stage pancreatic neoplasms. MR cholangiopancreatography has widely replaced endoscopic retrograde cholangiopancreatography in the diagnosis and staging of pancreatobiliary malignancies. MR imaging, using phased-array or endorectal coils, demonstrates local tumor invasion accurately in rectal cancers and thus allows an improved surgical planning. Virtual colonoscopy with MDCTs is an efficient screening method for colon cancer, and MDCT enterography is becoming the standard imaging technique for many small bowel disorders. The continuing developments in CT and MR technology will most probably further improve the accuracy of these and other imaging applications in the near future.