Spectrum of imaging findings in hyperplastic cholecystosis and potential mimics.

Adenomyomatosis and cholesterolosis of the gallbladder, collectively termed hyperplastic cholecystosis, are commonly encountered incidental findings on imaging studies performed for a variety of indications including biliary colic or nonspecific abdominal pain. These pathologies are rarely the source of symptoms, generally considered benign and do not require further work-up. However, their imaging characteristics can overlap with more sinister conditions that should not be missed. In this review, the imaging findings of adenomyomatosis and cholesterolosis will be reviewed followed by other gallbladder pathologies that might mimic these conditions radiologically. Important differentiating factors will be discussed that can aid the radiologist in making a more confident imaging diagnosis.

Volumetric growth rates of sessile serrated adenomas/polyps observed in situ at longitudinal CT colonography.

OBJECTIVE: Sessile serrated adenomas/polyps (SSA/Ps) are now recognized as potential cancer precursors, but little is known about their natural history. We assessed the in vivo growth rates of histologically proven SSA/Ps at longitudinal CT colonography (CTC) and compared results with non-advanced tubular adenomas (TAs). METHODS: We identified a cohort of 53 patients (mean age, 54.8 ± 5.5 years; M:F, 26:27) from one center with a total of 58 SSA/Ps followed longitudinally at CTC (mean follow-up interval, 5.3 ± 1.9 years). Initial and final size measurements were determined using dedicated CTC software. Findings were compared with 141 non-advanced TAs followed at CTC (mean, 4.1 ± 2.3 years) in 113 patients (mean age, 56.8 ± 6.9 years). RESULTS: SSA/Ps were more often flat (62% [36/58] vs. 14% [20/141], p < 0.0001) and right-sided (98% [57/58] vs. 46% [65/141], p < 0.0001) compared with TAs. Initial average diameter was greater for SSA/Ps (9.3 mm vs. 6.3 mm; p < 0.0001). Mean annual volumetric growth was + 12.7%/year for SSA/Ps vs. + 36.4%/year for TAs (p = 0.028). Using a previously defined threshold of + 20% increase in volume/year to define progression, 22% (13/58) of SSA/Ps and 41% (58/141) of TAs progressed (p = 0.014). None of the SSA/Ps had dysplasia or invasive cancer at histopathology. CONCLUSIONS: Sessile serrated adenoma/polyps demonstrate slower growth compared with conventional non-advanced tubular adenomas, despite larger initial linear size. This less aggressive behavior may help explain the more advanced patient age for serrated pathway cancers. Furthermore, these findings could help inform future colonoscopic surveillance strategies, as current guidelines are largely restricted to expert opinion related to the absence of natural history data. KEY POINTS: • Sessile serrated adenoma/polyps (SSA/Ps) tend to be flat, right-sided, and demonstrate slower growth compared with conventional non-advanced tubular adenomas. • This less aggressive behavior of SSA/Ps may help explain the more advanced patient age for serrated pathway cancers.

Detection of potentially relevant extracolonic and colorectal findings at CT colonography in a low-risk symptomatic patient population.

PURPOSE: CT colonography (CTC) is a widely accepted examination tool for detection of colorectal lesions but evidence of the proportions of relevant extracolonic findings (ECF) in a large symptomatic but still relatively low-risk cohort is lacking, as well as their relationship to symptoms, age, and sex. METHODS: All patients (n = 3208) with colorectal symptoms, imaged between January 2007 and September 2016 with first-time CTC, were retrospectively selected. The majority (96.7%) was examined with low-dose unenhanced protocol. The most relevant ECF and colorectal lesions (≥6 mm) were prospectively assessed according to C-RADS classifications. Follow-up was elaborated based on the electronic record review. Chi-square test was utilized for evaluating the associations between relevant findings and symptoms, age, and sex. RESULTS: A total of 270 (8.4%) patients were classified as C-RADS E3, 63 (2.0%) patients as C-RADS E4, and 437 (13.6%) patients were assessed with colorectal lesions (C-RADS C2-4). At follow-up, two thirds of ECF turned out to be a malignancy or relevant disease that required further medical attention. The proportion of ECF was not related to specific colorectal symptoms. Patients aged ≥65 years and men had significantly higher proportions of ECF than younger patients (C-RADS E3 p = 0.005; C-RADS E4 p < 0.001) and women (C-RADS E3 p = 0.013; C-RADS E4 p = 0.009), respectively. CONCLUSION: Proportions of relevant ECF and colorectal findings are relatively low in symptomatic low-risk patients. By use of CTC as a singular examination, especially in elderly patients, most colonoscopies can be avoided with the benefit of diagnosing relevant ECF without introducing substantial over-diagnosis.

Extramedullary haematopoiesis: radiological imaging features.

Extramedullary haematopoiesis (EMH) is defined as the production of blood cells outside of the bone marrow, which occurs when there is inadequate production of blood cells. The most common causes of EMH are myelofibrosis, diffuse osseous metastatic disease replacing the bone marrow, leukaemia, sickle cell disease, and thalassemia. The purpose of this article is to review the common and uncommon imaging appearances of EMH by anatomical compartment. In the thorax, EMH most commonly presents as paravertebral fat-containing masses, and typically does not present a diagnostic dilemma; however, EMH in the abdomen most commonly manifests as hepatosplenomegaly with or without focal soft-tissue masses in the liver, spleen, perirenal space, and in the peritoneum. Hepatosplenomegaly, a non-specific feature, most often occurs without an associated focal mass, which makes suggestion of EMH difficult. EMH manifesting as visceral soft-tissue masses often requires biopsy as the differential diagnosis can include lymphoma, metastatic disease, and sarcoma. Many of these soft-tissue masses do not contain adipose elements, making the diagnosis of EMH difficult. Clinical history is crucial, as EMH would likely not otherwise be in the differential in patients with non-specific abdominal masses. Careful biopsy planning is necessary when EMH is a diagnostic consideration, given the propensity for haemorrhage. Understanding the typical imaging appearances of EMH based on its site of manifestation can help the radiologist when encountered with a finding that is diagnostic for EMH, and can help the radiologist suggest the need and plan appropriately for image-guided biopsy.

Opportunistic screening for osteoporosis using the sagittal reconstruction from routine abdominal CT for combined assessment of vertebral fractures and density.

SUMMARY: Opportunistic osteoporosis screening using abdominal CT scans obtained for other purposes has the potential to increase detection of those at increased risk for fragility fractures. We sought to combine the tasks of density measurement and vertebral fracture assessment on the sagittal view. We confirm that this represents a robust approach and recommend its implementation in clinical practice. INTRODUCTION: Opportunistic osteoporosis screening at routine abdominal CT has been proposed by measuring axial (transverse) L1 trabecular attenuation and by sagittal reconstruction for vertebral fracture assessment. We sought to combine this dual evaluation on the sagittal reconstruction alone to improve efficiency. METHODS: Routine contrast-enhanced abdominal CT scans performed for any indication on 571 consecutive adults age 60 years or older (mean age 70.7 years) were retrospectively analyzed. These were performed at a single center over a 3-month period. L1 trabecular attenuation was measured using an ovoid region-of-interest on both the transverse and sagittal series. The sagittal reconstruction was also analyzed for moderate-to-severe vertebral compression fractures using the Genant visual semi-quantitative method. Likely osteoporosis was defined by a moderate-to-severe fracture and/or sagittal L1 trabecular attenuation of ≤110 Hounsfield units (HU) (previously found to be >90% specific for osteoporosis on our calibrated GE CT scanners at 120 kV(p)). Correlation was made with hip and spine dual X-ray absorptiometry (DXA). RESULTS: Mean absolute difference in L1 trabecular attenuation between transverse and sagittal reconstructions was 6.7 HU (±5.7) or 6.2%. The transverse and sagittal HU measurements were in agreement (i.e., both measurements above or below this threshold) in 94.5% of cases at the 110-HU cutoff. A total of 243 (42.3%) patients had likely osteoporosis by CT criteria, of which only 48 (19.8%) had previous DXA screening. CONCLUSION: Assessment of the sagittal view alone at routine abdominal CT for both vertebral fractures and trabecular bone mineral density provides a rapid and effective opportunistic screen for detecting individuals at increased risk for fragility fractures.

Effect of IV contrast on lumbar trabecular attenuation at routine abdominal CT: correlation with DXA and implications for opportunistic osteoporosis screening.

UNLABELLED: Osteoporosis remains under-diagnosed. Routine abdominal CT can provide opportunistic screening, but the effect of IV contrast is largely unknown. The overall performance for predicting osteoporosis was similar between enhanced and unenhanced scans. Therefore, both non-contrast and contrast-enhanced abdominal CT scans can be employed for opportunistic osteoporosis screening. INTRODUCTION: Osteoporosis is an important yet under-diagnosed public health concern. Lumbar attenuation measurement at routine abdominal CT can provide a simple opportunistic initial screen, but the effect of IV contrast has not been fully evaluated. METHODS: Mean trabecular CT attenuation values (in Hounsfield units, HU) at the L1 vertebral level were measured by oval region-of-interest (ROI) on both the unenhanced and IV-contrast-enhanced CT series in 157 adults (mean age, 62.0). All patients underwent correlative central DXA within 6 months of CT. Based on DXA BMD of the lumbar spine, femoral neck, and total proximal femur: osteoporosis, osteopenia, and normal BMD was present in 33, 77, and 47, respectively. Statistical analysis included Bland-Altman plots and receiver operating characteristic (ROC) curves. RESULTS: Mean difference (±SD) in L1 trabecular attenuation between enhanced and unenhanced CT series was +11.2 HU (±19.2) (95 % CI, 8.16-14.22 HU), an 8 % difference. Intra-patient variation was substantial, but no overall trend in the HU difference was seen according to underlying BMD. ROC area under the curve (AUC) for unenhanced and enhanced CT for diagnosing osteoporosis were similar at 0.818 and 0.830, respectively (p = 0.632). Thresholds for maintaining 90 % specificity for osteoporosis were 90 HU for unenhanced and 102 HU for enhanced CT. Thresholds for maintaining 90 % sensitivity for osteoporosis were 139 HU for unenhanced and 144 HU for enhanced CT. Similar diagnostic performance was seen for diagnosing low BMD (osteoporosis or osteopenia) using higher HU cut-offs. CONCLUSION: Contrast-enhanced CT shows an average increase of 11 HU over the unenhanced series for L1 trabecular attenuation. The overall performance for predicting osteoporosis is similar between the enhanced and unenhanced scans, thus either can be employed for initial opportunistic screening.

Intra-individual comparison of magnesium citrate and sodium phosphate for bowel preparation at CT colonography: automated volumetric analysis of residual fluid for quality assessment.

AIM: To perform an objective, intra-individual comparison of residual colonic fluid volume and attenuation associated with the current front-line laxative magnesium citrate (MgC) versus the former front-line laxative sodium phosphate (NaP) at CT colonography (CTC). MATERIALS AND METHODS: This retrospective Health Insurance and Portability and Accountability Act-compliant study had institutional review board approval; informed consent was waived. The study cohort included 250 asymptomatic adults (mean age at index 56.1 years; 124 male/126 female) who underwent CTC screening twice over a 5 year interval. Colon catharsis at initial and follow-up screening employed single-dose NaP and double-dose MgC, respectively, allowing for intra-patient comparison. Automated volumetric analysis of residual colonic fluid volume and attenuation was performed on all 500 CTC studies. Colonic fluid volume <200 ml and mean attenuation between 300-900 HU were considered optimal. Paired t-test and McNemar's test were used to compare differences. RESULTS: Residual fluid volumes <200 ml were recorded in 192 examinations (76.8%) following MgC and in 204 examinations (81.6%) following NaP (p = 0.23). The mean total residual fluid volume was 155 ± 114 ml for MgC and 143 ± 100 ml for NaP (p = 0.01). The attenuation range of 300-900 HU was significantly more frequent for MgC (n = 220, 88%) than for NaP (n = 127, 50.8%; p < 0.001). Mean fluid attenuation was significantly lower for MgC (700 ± 165 HU) than for NaP (878 ± 155 HU; p < 0.001). Concomitant presence of both optimal fluid volume and attenuation was significantly more frequent for MgC 65.2% than for NaP (38%; p < 0.001). CONCLUSIONS: Objective intra-individual comparison using automated volumetric analysis suggests that the replacement of NaP by MgC as the front-line laxative for CTC has not compromised overall examination quality.

Impact of lifestyle factors on colorectal polyp detection in the screening setting.

BACKGROUND: Awareness of risk factors for colorectal neoplasia could address risk reduction strategies in asymptomatic subjects. METHODS: This is a post hoc analysis of a prospective, cross-sectional study of 1321 asymptomatic adults. All the subjects underwent same-day CT colonography and colonoscopy to determine the prevalence of colorectal neoplasia. The variables examined included body mass index, smoking, alcohol consumption, age, and gender. Univariate and logistic regression analyses were performed for detection of colorectal neoplasia and hyperplastic polyps. Odds ratios with 95% confidence intervals were calculated. RESULTS: Colorectal adenomas and hyperplastic polyps were detected in 378 (28.6%) and 157 (11.9%) participants, respectively. In both univariate and multivariate analysis, increasing age, male gender, and body mass index > or =25 were significantly associated with the detection of colorectal adenomas, with an odds ratio of 1.22 (95% CI,1.09-1.36), 1.28 (95% CI, 1.06-1.45), and 1.34 (95% CI, 1.02-1.77), respectively. A history of smoking was the only identifiable risk factor for hyperplastic polyps (odds ratio, 1.98; 95% CI, 1.41-2.78). CONCLUSIONS: Body mass index > or =25, increasing age, and male gender were all associated with an increased likelihood of colorectal adenomas at screening, whereas smoking was strongly associated with hyperplastic polyps.

Systematic review: distribution of advanced neoplasia according to polyp size at screening colonoscopy.

BACKGROUND: The impact of not referring sub-centimetre polyps identified at CT colonography upon the efficacy of colorectal cancer screening remains uncertain. AIM: To determine the distribution of advanced neoplasia according to polyp size in a screening setting. METHODS: Published studies reporting the distribution of advanced adenomas in asymptomatic screening cohorts according to polyp size were identified by MEDLINE and EMBASE searches. Predefined outputs were the screening rates of advanced adenomas represented by diminutive (< or =5 mm), small (6-9 mm), sub-centimetre (<10 mm) and large (> or =10 mm) polyp sizes. RESULTS: Data from four studies with 20 562 screening subjects met the primary inclusion criteria. Advanced adenomas were detected in 1155 (5.6%) subjects (95% CI = 5.3-5.9), corresponding to diminutive, small and large polyps in 4.6% (95% CI = 3.4-5.8), 7.9% (95% CI = 6.3-9.4) and 87.5% (95% CI = 86-89.4) of cases respectively. The frequency of advanced lesions among patients whose largest polyp was diminutive, small, sub-centimetre and large in size was 0.9%, 4.9%, 1.7% and 73.5% respectively. CONCLUSIONS: Based on this systematic review, a 6-mm polyp size threshold for polypectomy referral would identify over 95% of subjects with advanced adenomas, whereas a 10-mm threshold would identify 88% of cases.

Colorectal anatomy in adults at computed tomography colonography: normal distribution and the effect of age, sex, and body mass index.

BACKGROUND AND STUDY AIMS: Computed tomography colonography (CTC) is an accurate tool for assessing the large intestinal anatomy. Our aims were to determine the normal distribution of in vivo colorectal anatomy and to investigate the effect of age, sex, and body mass index (BMI) on colorectal length. PATIENTS AND METHODS: Asymptomatic adults who underwent primary CTC examination at a single institution over an 8-month period were evaluated. The interactive three-dimensional map was used to determine total and segmental lengths and number of acute-angle flexures. The two-dimensional multiplanar display was used to measure luminal diameters. The effects of age, sex, and BMI on colorectal lengths were examined. RESULTS: The study cohort consisted of 505 consecutive adults (266 women, mean age 56.6 years). Mean total colorectal length was 189.5 +/- 26.3 cm and mean number of acute-angle flexures was 10.9 +/- 2.4. Total length for older adults (> 60 years) did not significantly differ from those who were younger than 60 years ( P = 0.22), although the transverse colon was significantly longer in older adults ( P = 0.04). Women had significantly longer colons than men (193.3 cm vs. 185.4 cm, P = 0.002), whereas overweight adults (BMI > 25) had significantly shorter colons compared with those with BMI

Cost-effectiveness of early colonoscopy surveillance after cancer resection.

BACKGROUND: Short-interval surveillance colonoscopy at 1 year has been recently recommended following curative-intent surgery for colorectal cancer. However, the efficacy and cost-effectiveness of this endoscopic strategy is largely unknown. AIM: To assess the clinical and economic impact of early surveillance post-surgical colonoscopy at 1 year in relation to the detection of metachronous colorectal cancer. METHODS: A decision analysis model was constructed in order to compare a strategy of 1-year endoscopic surveillance versus no early endoscopy following surgical resection for colorectal cancer. A 2-year cancer upstaging was modelled in order to simulate cancer progression in patients with metachronous colorectal cancer who were not referred to early endoscopy. Endoscopic prevalence of metachronous colorectal cancer was estimated from a previous pooled data analysis based on systematic review of the literature. Costs of colonoscopy and cancer care were estimated from Medicare reimbursement data. Outcome measures were the number of early colonoscopies needed to detect one case of cancer or to prevent one cancer-related death and the incremental cost-effectiveness ratio. RESULTS: The number of early 1-year colonoscopies needed to detect one colorectal cancer and to prevent one colorectal cancer-related death was 143 and 926, respectively. The incremental cost-effectiveness ratio of the early 1-year colonoscopy as compared to a policy of not performing it was $40,313 per life-year gained. The incremental cost-effectiveness ratio of performing early surveillance colonoscopy was sensitive to the changes in cancer prevalence. However, only a reduction from the baseline value of 0.7% to 0.19% was associated with an incremental cost-effectiveness ratio higher than $150,000. Other assumptions about cancer upstaging, initial distribution of cancer, and costs had a lesser influence on incremental cost-effectiveness ratio differences. CONCLUSIONS: Our study shows that the recently recommended short-interval 1-year surveillance colonoscopy following colorectal cancer resection is a clinically efficient and cost-effective strategy in terms of cancer detection and cancer-specific death prevention.

Effect of visualization display colour on polyp conspicuity at virtual colonoscopy.

AIM: To investigate the effect of different colour three-dimensional (3D) displays on polyp detection at virtual colonoscopy (VC). METHODS: Five VC trained observers were shown "brief flashes" (lasting 0.2s) of 125 3D endoluminal image snap-shots, repeated for each of six display colours (750 images total). One hundred images contained a single polyp (diameter range 5-42 mm) and 25 contained no polyp ("normal"). Images were reviewed in random order over five reading sessions, readers recording either normality or presence and location of a polyp. Multilevel logistic regression was used to examine any influence of colour on polyp detection stratified according to polyp size (medium 5-9 mm/large >or=10mm). The kappa statistic was used to assess effect of colour on observer agreement. RESULTS: Individual reader polyp detection rates ranged between 75-94%. Compared to the default pink "soft tissue" display, the odds of polyp detection were 0.65 (CI 0.41,1.01) for green, 0.82 (0.53,1.30) for blue, 1 (0.63,1.59) for red, 1.12 (0.7,1.79) for monochrome, and 1.15 for yellow (0.72,1.84). Overall, there was no significant difference between the displays (p=0.11). Including normal cases, there was no overall difference in correct case classification between the six colours (p=0.44). The odds of detecting large versus medium polyps was significantly greater for 3/5 observers; odds ratio (OR) 2.84-10.1, although unaffected by display colour (p=0.3). CONCLUSION: The background colour display generally has a minimal effect on polyp detection at VC, although green should be avoided.

Virtual colonoscopy: effect of computer-assisted detection (CAD) on radiographer performance.

AIM: To investigate the effect of a virtual colonoscopy (VC) computed-assisted detection (CAD) system on polyp detection by trained radiographers. MATERIALS AND METHODS: Four radiographers trained in VC interpretation and utilization of CAD systems read a total of 62 endoscopically validated VC examinations containing 150 polyps (size range 5-50mm) in four sessions, recording any polyps found and the examination interpretation time, first without and then with the addition of CAD as a "second reader". After a temporal separation of 6 weeks to reduce recall bias, VC examinations were re-read using "concurrent reader" CAD. Interpretation times, polyp detection, and number of false-positives were compared between the different reader paradigms using paired t and paired exact tests. RESULTS: Overall, use of "second reader" CAD significantly improved polyp detection by 12% (p<0.001, CI 6%,17%)) from 48 to 60%. There was no significant improvement using CAD as a concurrent reader (p=0.20; difference of 7%, CI -3%, 16%) and no significant overall difference in recorded false-positives with second reader or concurrent CAD paradigms compared with unassisted reading (p=0.25 and 0.65, respectively). The mean interpretation time was 21.7 min for unassisted reading, 29.6 (p<0.001) min for second reader and 19.1 min (p=0.12) for concurrent reading paradigms. CONCLUSION: CAD, when used as a second reader, can significantly improve radiographer reading performance with only a moderate increase in interpretation times.

Projected impact of colorectal cancer screening with computerized tomographic colonography on current radiological capacity in Europe.

BACKGROUND: The impact of a primary colorectal cancer screening with computerized tomographic colonography on current radiological capacity is unknown. The multispecialty needs for computerized tomographic examinations raise some doubts on the feasibility of a mass colorectal cancer screening with computerized tomographic colonography. AIM: To assess whether the number of available computerized tomographic units in Europe is adequate to cover population screening with computerized tomographic colonography. METHODS: A mathematical and a Markov model were, respectively, used to assess the number of computerized tomographic colonography procedures needed to be performed each day in the start-up and in the steady-state phases of a colorectal cancer screening programme in Europe. Such outcome was divided for the total number of computerized tomographic machines aged <10 years estimated to be present in the European hospitals. RESULTS: At a simulated 30% compliance, 28 760 130 European people would need to be screened by the 3482 available computerized tomographic units in a 5-year start-up period, corresponding to 6.6 CTC/CT unit/day. Assuming a 10-year repetition of computerized tomographic colonography between 50 and 80 years, the number of computerized tomographic colonography needed to be performed in the steady-state period appeared to be 4.3/CT unit/day. CONCLUSIONS: The current radiological capacity may cover the need for a primary colorectal cancer screening with computerized tomographic colonography in a steady state. On the other hand, a substantial implementation of the current computerized tomographic capacity or a synergistic approach with other techniques seems to be necessary for the start-up period.

Computed tomographic colonography for colorectal screening.

Computed tomographic colonography (CTC) is a specialized computed tomographic examination that has been optimized for the detection of colorectal polyps. The technology has undergone major advances in recent years and there is emerging consensus that state-of-the-art CTC results in performance characteristics comparable to those of optical colonoscopy for polyps > or = 8 mm in size. Effective polyp detection rests on the quality of several components of the examination, which must all be optimized in order to maintain appropriate sensitivity and specificity, including adequate bowel preparation, good colonic distension, sufficient scanning parameters, and appropriate interpretation. The emergence of CTC provides another method of colonic evaluation for colorectal cancer screening and prevention. In contrast to a mutually exclusive approach to screening, the availability of both optical colonoscopy and CTC should hopefully improve overall compliance rates for colorectal screening. The ultimate role of this technique in the screening program continues to evolve. There is currently considerable variability in the materials and methods used in CTC. This article describes the approach used at the University of Wisconsin, which has been validated in a large multicenter screening trial and which is currently used for an active CTC-based colorectal cancer screening program.

Virtual colonoscopy for primary screening. The future is now.

Virtual colonoscopy (VC) is a minimally invasive tool that utilizes modern CT technology for colorectal evaluation. Since its inception in 1994, VC has continued to rapidly evolve and improve as a diagnostic screening tool. Early success using primary two-dimensional (2D) detection in polyp-rich cohorts was followed by disappointing results in low prevalence populations. Subsequent introduction of the three-dimensional (3D) endoluminal display for primary polyp detection and oral contrast tagging has transformed VC into an effective primary screening tool. This state-of-the-art VC technique has already proven to be a viable enterprise when combined with existing optical colonoscopy practice. More widespread implementation of VC screening faces multiple challenges, but these are all greatly overshadowed by the immediate need for increased participation in effective colorectal screening. Given its relatively noninvasive nature and the wide availability of CT, VC holds significant potential for addressing a very important yet preventable public health concern. This review will cover current VC technique, compare the existing multi-center VC trials, discuss issues related to primary VC screening, and briefly update the progress of our VC screening program.

Collecting duct carcinoma of the kidney: are imaging findings suggestive of the diagnosis?

OBJECTIVE: Collecting duct carcinoma derives from the renal medulla and has an infiltrative growth pattern at pathologic examination. The purpose of our study was to characterize the imaging features of this aggressive malignancy and determine whether the diagnosis can be reliably suggested from imaging findings. MATERIALS AND METHODS: Radiologic studies from 17 patients with pathologically proven collecting duct carcinoma were analyzed by two reviewers. RESULTS: The tumors varied in size from 1.5 to 19 cm (mean, 7.7 cm). Medullary involvement was present on CT in 16 (94%) of 17 cases, but cortical involvement or an exophytic component was also present in 15 cases (88%) and 10 cases (59%), respectively. The reniform contour of the kidney was preserved in seven cases (41%) and correlated with a smaller tumor size (p<0.01). Tumors showed an infiltrative appearance on CT in 11 cases (65%), but an expansile component was also present in eight of these cases. A cystic component was present on CT in six (35%) of 17 cases. On sonography, the solid tumor component was hyperechoic to normal renal parenchyma in six of seven cases and isoechoic in the other. On MR imaging, all tumors (4/4) were hypointense on T2-weighted imaging. On urography, all lesions (5/5) distorted the intrarenal collecting system. On angiography, all tumors (3/3) were hypovascular. CONCLUSION: Medullary involvement and an infiltrative appearance are common findings on cross-sectional imaging and may suggest the diagnosis of collecting duct carcinoma. In large tumors, however, these features are frequently overshadowed by an exophytic or expansile component that cannot be distinguished from the more common cortical renal cell carcinoma.