Search

Background Differences in the clinical and radiological characteristics of SARS-CoV-2 Omicron subvariants have not been well studied. Purpose To compare clinical disease severity and radiologically severe pneumonia in patients with COVID-19 hospitalized during a period of either Omicron BA.1/BA.2 or Omicron BA.5 subvariant predominance. Materials and Methods This multicenter retrospective study, included patients registered in the Korean Imaging Cohort of COVID-19 database who were hospitalized for COVID-19 between January and December 2022. Publicly available relative variant genome frequency data were used to determine the dominant periods of Omicron BA.1/BA.2 subvariants (January 17 to June 20, 2022) and the Omicron BA.5 subvariant (July 4 to December 5, 2022). Clinical outcomes and imaging pneumonia outcomes based on chest radiography and CT were compared among predominant subvariants using multivariable analyses adjusted for covariates. Results Of 1916 confirmed patients with COVID-19 (mean age, 72 years ± 16 [SD]; 1019 males), 1269 were registered during the Omicron BA.1/BA.2 subvariant dominant period and 647 during the Omicron BA.5 subvariant dominant period. Patients in the BA.5 group showed lower odds of high-flow O 2 requirement (adjusted odds ratio [OR], 0.75 [95% CI: 0.57, 0.99]; P = .04), mechanical ventilation (adjusted OR, 0.49 [95% CI: 0.34, 0.72]; P < .001]), and death (adjusted OR, 0.47 [95% CI: 0.33, 0.68]; P <.001) than those in the BA.1/BA.2 group. Additionally, the BA.5 group had lower odds of severe pneumonia on chest radiographs (adjusted OR, 0.68 [95% CI: 0.53, 0.88]; P = .004) and higher odds of atypical pattern pneumonia on CT images (adjusted OR, 1.81 [95% CI: 1.26, 2.58]; P = .001) than the BA.1/BA.2 group. Conclusions Patients hospitalized during the period of Omicron BA.5 subvariant predominance had lower odds of clinical and pneumonia severity than those hospitalized during the period of Omicron BA.1/BA.2 predominance, even after adjusting for covariates. See also the editorial by Hammer in this issue.

Background Few reports have evaluated the effect of the SARS-CoV-2 variant and vaccination on the clinical and imaging features of COVID-19. Purpose To evaluate and compare the effect of vaccination and variant prevalence on the clinical and imaging features of infections by the SARS-CoV-2. Materials and Methods Consecutive adults hospitalized for confirmed COVID-19 at three centers (two academic medical centers and one community hospital) and registered in a nationwide open data repository for COVID-19 between August 2021 and March 2022 were retrospectively included. All patients had available chest radiographs or CT images. Patients were divided into two groups according to predominant variant type over the study period. Differences between clinical and imaging features were analyzed with use of the Pearson χ 2 test, Fisher exact test, or the independent t test. Multivariable logistic regression analyses were used to evaluate the effect of variant predominance and vaccination status on imaging features of pneumonia and clinical severity. Results Of the 2180 patients (mean age, 57 years ± 21; 1171 women), 1022 patients (47%) were treated during the Delta variant predominant period and 1158 (53%) during the Omicron period. The Omicron variant prevalence was associated with lower pneumonia severity based on CT scores (odds ratio [OR], 0.71 [95% CI: 0.51, 0.99; P = .04]) and lower clinical severity based on intensive care unit (ICU) admission or in-hospital death (OR, 0.43 [95% CI: 0.24, 0.77; P = .004]) than the Delta variant prevalence. Vaccination was associated with the lowest odds of severe pneumonia based on CT scores (OR, 0.05 [95% CI: 0.03, 0.13; P < .001]) and clinical severity based on ICU admission or in-hospital death (OR, 0.15 [95% CI: 0.07, 0.31; P < .001]) relative to no vaccination. Conclusion The SARS-CoV-2 Omicron variant prevalence and vaccination were associated with better clinical outcomes and lower severe pneumonia risk relative to Delta variant prevalence. © RSNA, 2022 Supplemental material is available for this article. See also the editorial by Little in this issue.

Background Since vaccines against COVID-19 became available, rare breakthrough infections have been reported despite their high efficacies. Purpose To evaluate the clinical and imaging characteristics of patients with COVID-19 breakthrough infections and compare them with those of unvaccinated patients with COVID-19. Materials and Methods In this retrospective multicenter cohort study, the authors analyzed patient (aged ≥18 years) data from three centers that were registered in an open data repository for COVID-19 between June and August 2021. Hospitalized patients with baseline chest radiographs were divided into three groups according to their vaccination status. Differences between clinical and imaging features were analyzed using the Pearson χ 2 test, Fisher exact test, and analysis of variance. Univariable and multivariable logistic regression analyses were used to evaluate associations between clinical factors, including vaccination status and clinical outcomes. Results Of the 761 hospitalized patients with COVID-19, the mean age was 47 years and 385 (51%) were women; 47 patients (6%) were fully vaccinated (breakthrough infection), 127 (17%) were partially vaccinated, and 587 (77%) were unvaccinated. Of the 761 patients, 412 (54%) underwent chest CT during hospitalization. Among the patients who underwent CT, the proportions without pneumonia were 22% of unvaccinated patients (71 of 326), 30% of partially vaccinated patients (19 of 64), and 59% of fully vaccinated patients (13 of 22) ( P < .001). Fully vaccinated status was associated with a lower risk of requiring supplemental oxygen (odds ratio [OR], 0.24 [95% CI: 0.09, 0.64; P = .005]) and lower risk of intensive care unit admission (OR, 0.08 [95% CI: 0.09, 0.78; P = .02]) compared with unvaccinated status. Conclusion Patients with COVID-19 breakthrough infections had a significantly higher proportion of CT scans without pneumonia compared with unvaccinated patients. Vaccinated patients with breakthrough infections had a lower likelihood of requiring supplemental oxygen and intensive care unit admission. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Schiebler and Bluemke in this issue.

Background Multicenter studies are required to validate the added benefit of using deep convolutional neural network (DCNN) software for detecting malignant pulmonary nodules on chest radiographs. Purpose To compare the performance of radiologists in detecting malignant pulmonary nodules on chest radiographs when assisted by deep learning-based DCNN software with that of radiologists or DCNN software alone in a multicenter setting. Materials and Methods Investigators at four medical centers retrospectively identified 600 lung cancer-containing chest radiographs and 200 normal chest radiographs. Each radiograph with a lung cancer had at least one malignant nodule confirmed by CT and pathologic examination. Twelve radiologists from the four centers independently analyzed the chest radiographs and marked regions of interest. Commercially available deep learning-based computer-aided detection software separately trained, tested, and validated with 19 330 radiographs was used to find suspicious nodules. The radiologists then reviewed the images with the assistance of DCNN software. The sensitivity and number of false-positive findings per image of DCNN software, radiologists alone, and radiologists with the use of DCNN software were analyzed by using logistic regression and Poisson regression. Results The average sensitivity of radiologists improved (from 65.1% [1375 of 2112; 95% confidence interval {CI}: 62.0%, 68.1%] to 70.3% [1484 of 2112; 95% CI: 67.2%, 73.1%], P < .001) and the number of false-positive findings per radiograph declined (from 0.2 [488 of 2400; 95% CI: 0.18, 0.22] to 0.18 [422 of 2400; 95% CI: 0.16, 0.2], P < .001) when the radiologists re-reviewed radiographs with the DCNN software. For the 12 radiologists in this study, 104 of 2400 radiographs were positively changed (from false-negative to true-positive or from false-positive to true-negative) using the DCNN, while 56 of 2400 radiographs were changed negatively. Conclusion Radiologists had better performance with deep convolutional network software for the detection of malignant pulmonary nodules on chest radiographs than without. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Jacobson in this issue.

Purpose To identify the features at CT that are predictive of spread through air spaces (STAS) in surgically resected lung adenocarcinomas. Materials and Methods For this retrospective study, presence of STAS was evaluated in 948 consecutive patients who underwent surgical resection for lung adenocarcinoma from April 2015 to December 2016. Patients who were positive for STAS and negative for STAS were matched at a ratio of 1:2 by using patient variables (age, sex, and smoking status). CT features (ie, percentage of solid component, maximum diameter of solid component, lesion density, location, margin, shape, pseudocavity, calcification, central low attenuation, ill-defined peripheral opacity, air bronchogram, satellite lesions, and pleural retraction) were analyzed by using multivariable logistic regression and receiver operating characteristic curves. Results The final study population consisted of 276 patients (mean age, 59 years; age range, 32-78 years) including 129 men (mean age, 60 years; age range, 36-78 years) and 147 women (mean age, 59 years; age range, 32-78 years). Ninety-two patients were positive for STAS and 184 patients were negative for STAS. STAS was more common in solid tumors (71 of 92; 77%) than in part-solid (21 of 92; 23%) or ground-glass lesions (0 of 92; 0%) (P < .001). STAS was also associated with central low attenuation, ill-defined opacity, air bronchogram, and percentage of solid component (all P < .001). Percentage of solid component was an independent predictor of STAS (odds ratio, 1.06; 95% confidence interval: 1.03, 1.08) and a cut-off value of 90% showed a discriminatory power with a sensitivity of 89.2% and a specificity of 60.3%. Conclusion Percentage of solid component was independently associated with spread through air spaces in lung adenocarcinomas. © RSNA, 2018 Online supplemental material is available for this article.

Purpose: To evaluate the feasibility and safety of repeat biopsy for mutational analysis in patients with non-small cell lung cancer (NSCLC) who have a resistance history to previous chemotherapy., Materials and Methods: This prospective study was institutional review board approved, and written informed consent was obtained from all patients. Of 126 patients referred for repeat biopsy (hereafter, rebiopsy) with NSCLC that was resistant to conventional chemotherapy or epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors, 94 patients (31 men, 63 women; mean age ± standard deviation, 57 years ± 10.3) were selected for rebiopsy. Thirty-two patients were excluded for several reasons after strict review of the chest computed tomography (CT) images. Percutaneous transthoracic lung biopsy was performed with C-arm cone-beam CT guidance. The technical success rates for the rebiopsy and the adequacy rates of specimens for mutational analysis were evaluated. Any biopsy-related complications were recorded., Results: The technical success rate for biopsy was 100%. In 75 (80%) of 94 patients, specimens were adequate for mutational analysis. Of 75 specimens, 35 were tested for EGFR mutation, 34 for anaplastic lymphoma kinase gene (ALK) rearrangement, and six for both. The results were positive for EGFR-sensitizing mutation (exon 19 or 21) in 20, for EGFR T790M mutation in five, and for ALK rearrangement in 11. Postprocedural complications occurred in 13 (14%) of 94 patients., Conclusion: When performed by employing rigorous CT criteria, rebiopsies for the mutational analysis of NSCLCs treated previously with chemotherapy are feasible in all patients and are adequate in approximately four-fifths of patients referred for gene analysis, with acceptable rates of complications., (© RSNA, 2012.)

Purpose: To compare the diagnostic performance of a low-radiation-dose digital tomosynthesis (DTS) technique with that of conventional radiography in the detection of lung lesions in patients with pulmonary mycobacterial disease., Materials and Methods: The institutional review board approved this study, and all patients provided informed consent. In this study, 100 patients (65 study patients, 35 control patients) underwent multidetector computed tomography (CT), chest radiography, and low-dose DTS (effective doses: 3.4, 0.02, and 0.05 mSv, respectively). Two radiologists evaluated radiographs and DTS images for the presence of parenchymal lesions and the number of cavities in each patient; CT served as the reference standard. Wilcoxon signed rank and McNemar tests and κ statistics were used., Results: The accuracies of DTS and radiography in depicting mycobacterial disease were 97% and 89%, respectively, for observer 1 (P = .039) and 99% and 93%, respectively, for observer 2 (P = .031). The accuracies of DTS and radiography in depicting each lesion type were, respectively, 95% and 77% for bronchiolitis, 92% and 76% for nodules, 86% and 79% for consolidation, and 93% and 70% for cavities. Interobserver agreement with DTS (κ = 0.62-0.94) was superior to that with radiography (κ = 0.46-0.62). Of a total of 141 cavities found with CT, means of 27 (19%) cavities at chest radiography and 108 (77%) cavities at DTS (P < .01) were detected by the two observers., Conclusion: DTS performed with a low-dose technique is superior to radiography for the detection of lung lesions in patients with pulmonary mycobacterial disease.

Purpose: To evaluate the utility of clinical, thin-section computed tomography (CT), and histopathologic findings in predicting the prognosis of patients with usual interstitial pneumonia (UIP) or fibrotic nonspecific interstitial pneumonia (NSIP)., Materials and Methods: The institutional review board approved this retrospective study, with waiver of informed consent. Included were 108 patients (71 men, 37 women; mean age, 61 years +/- 8 [standard deviation]) with UIP (n = 79; 60 men, 19 women; mean age, 63 years +/- 7.4) and fibrotic NSIP (n = 29; 11 men, 18 women; mean age, 57 years +/- 12.9). Patients underwent pulmonary function tests (PFTs), bronchoalveolar lavage (BAL) fluid analysis, and thin-section CT. Two chest radiologists independently assigned scores for the extent of lung abnormalities detected at CT twice at 3-month intervals. The effect of histopathologic diagnoses and clinical and thin-section CT features on survival was evaluated by using Cox regression analyses., Results: The 5-year survival rate (mean follow-up, 45 months) of patients with fibrotic NSIP was 76% in contrast to 46% for patients with UIP (P = .006). With multivariate analysis, a high fibrotic score (the extent of reticulation plus honeycombing) (hazard ratio = 1.200, P = .043) and an initial low diffusing capacity of lung for carbon monoxide (Dlco) level (hazard ratio = 0.973, P = .025) were identified as associated with increased death risk., Conclusion: Patients with UIP or fibrotic NSIP who have a high fibrotic score determined at thin-section CT and a low Dlco level appear to have a high death risk., ((c) RSNA, 2008.)

Purpose: To prospectively evaluate the diagnostic accuracy of 3.0-T magnetic resonance (MR) imaging in the detection of non-small cell lung cancer nodal metastasis, with histopathologic analysis as the reference standard., Materials and Methods: Institutional review board approval and informed consent were obtained. From July 2005 to May 2006, 113 patients (91 men, 22 women; age range, 34-82 years; mean age, 61 years) with non-small cell lung cancer underwent thoracic 3.0-T MR imaging followed by surgery or mediastinoscopy. The lymph node-to-tumor ratios (LTRs) of signal intensity and nodal morphologic characteristics (such as eccentric cortical thickening or obliteration of the fatty hilum) were assessed on T2-weighted triple-inversion black-blood fast spin-echo images. Nodal short-axis diameter was assessed on T1-weighted three-dimensional fast field-echo images. Receiver operating characteristic and multivariate logistic regression analyses were used for statistical evaluation., Results: The cutoff value (LTR > 0.84) proved to be most appropriate (area under the receiver operating characteristic curve = 0.735, P < .001) in the detection of a nodal metastasis. Of the various parameters examined, morphologic characteristics appeared to be the most significant (P < .001) parameters for depicting a malignant node (multivariate logistic regression analyses; odds ratio, 7.5). Nodal morphology was analyzed, and diagnostic sensitivity, specificity, and accuracy were 53% (39 of 74 nodal stations), 91% (453 of 496 nodal stations), and 86% (492 of 570 nodal stations), respectively., Conclusion: Morphologic details of lymph nodes on T2-weighted triple-inversion black-blood fast spin-echo MR images are significant for detection of mediastinal or hilar nodal metastasis at 3.0-T MR imaging., ((c) RSNA, 2007.)

Purpose: To prospectively assess the accuracy of combined wash-in and washout characteristics at dynamic contrast material-enhanced multi-detector row computed tomography (CT) in distinguishing benign from malignant solitary pulmonary nodules., Materials and Methods: Institutional review board approval and informed consent were obtained. The study included 107 patients (62 men, 45 women; mean age, 55 years; range, 22-81 years) with a solitary pulmonary nodule. After unenhanced CT (2.5-mm collimation) scans were obtained, dynamic CT was performed by using a helical technique (series of images obtained throughout the nodule, with 2.5-mm collimation, at 30, 60, 90, and 120 seconds and 4, 5, 9, 12, and 15 minutes) after intravenous injection of contrast medium (120 mL). Tissue diagnosis was made in 70 nodules, and follow-up images showed benignancy in the remaining 37 (no change in size, n = 32; decrease in size, n = 5). CT findings were analyzed in terms of wash-in and washout of contrast medium. Sensitivity, specificity, and accuracy for malignant nodules were calculated by considering both the wash-in and washout characteristics at dynamic CT., Results: There were 49 malignant and 58 benign nodules. When diagnostic criteria for malignancy of both wash-in of 25 HU or greater and washout of 5-31 HU were applied, sensitivity, specificity, and accuracy for malignancy were 94% (46 of 49 nodules), 90% (52 of 58 nodules), and 92% (98 of 107 nodules), respectively. Of 58 benign nodules, 27 showed less than 25 HU wash-in, 14 showed persistent contrast enhancement without washout and with wash-in of 25 HU or greater, and 11 showed washout greater than 31 HU and wash-in of 25 HU or greater., Conclusion: Evaluation of solitary pulmonary nodules by analyzing combined wash-in and washout characteristics at dynamic contrast-enhanced multi-detector row CT showed 92% accuracy for distinguishing benign nodules from malignant nodules.

Purpose: To evaluate prospectively the accuracy of integrated positron emission tomography (PET) and computed tomography (CT) with use of fluorodeoxyglucose (FDG), compared with that of stand-alone CT, for the preoperative staging of non-small cell lung cancer, with surgical and histologic findings used as the reference standard., Materials and Methods: Institutional review board approval and patient informed consent were obtained. From November 2003 to February 2004, 106 patients (78 men, 28 women; mean age, 56 years) with non-small cell lung cancer underwent curative surgical resection (tumor resection and lymph node dissection) after stand-alone CT followed by integrated FDG PET/CT. Tumor stages were determined by using the TNM and American Joint Committee on Cancer staging systems. Histopathologic results served as the reference standard. Statistically significant differences in tumor staging between integrated PET/CT and stand-alone CT were determined with P < .05 obtained by using the McNemar test or with a generalized estimating equation., Results: The primary tumor was correctly staged in 84 patients (79%) at stand-alone CT and in 91 patients (86%) at integrated FDG PET/CT (P = .25). For the depiction of malignant nodes, the sensitivity, specificity, and accuracy of CT were 70% (23 of 33 nodal groups), 69% (248 of 360), and 69% (271 of 393), respectively, whereas those of PET/CT were 85% (28 of 33), 84% (302 of 360), and 84% (330 of 393) (P = .25, P < .001, and P < .001, respectively). There were 112 false-positive interpretations at CT for 54 hilar, 16 subcarinal, 29 paratracheal, 10 subaortic, and two pulmonary ligament nodal groups and one upper paratracheal group, compared with only 58 false-positive interpretations at PET/CT for 32 hilar, seven subcarinal, 13 lower paratracheal, and six subaortic nodal groups. There were 10 false-negative interpretations at CT for four hilar, two lower paratracheal, and two subcarinal nodal groups, one prevascular and retrotracheal group, and one inferior pulmonary group, but only five false-negative interpretations at PET/CT (one each for paratracheal, subaortic, subcarinal, inferior pulmonary, and hilar nodal groups)., Conclusion: Integrated FDG PET/CT is significantly better than stand-alone CT for lung cancer staging and provides enhanced accuracy and specificity in nodal staging.

Purpose: To retrospectively evaluate 16-detector row computed tomography (CT) compared with conventional angiography in depiction of bronchial and nonbronchial systemic arteries in patients with hemoptysis., Materials and Methods: Institutional review board approval was obtained, and informed consent was not required. Sixteen-detector row helical CT and conventional angiography of the thorax were performed in 22 patients (16 men, six women; age range, 18-75 years; mean age, 50 years) with hemoptysis. Three observers in consensus analyzed retrospectively transverse, multiplanar reconstruction, or three-dimensional CT images for visibility, traceability of bronchial arteries from their origin at the aorta or aortic branches to the hilum, and presence of nonbronchial systemic arteries. CT and angiographic findings of bronchial and nonbronchial systemic arteries causing hemoptysis were compared by two radiologists in consensus. Differences in visibility, traceability, and diameter of bronchial arteries causing and those not causing hemoptysis were tested by using generalized estimating equation method or the mixed model., Results: Fifty-two (30 right and 22 left) bronchial arteries and 33 nonbronchial systemic arteries were visible at CT. Thirty-four (20 right and 14 left) of 52 bronchial arteries were traceable from their origins to the hilum. Thirty-one (16 right and 15 left) of 46 (27 right and 19 left) bronchial arteries and 26 of 64 nonbronchial systemic arteries evaluated at angiography were causing hemoptysis. Forty (87%, 23 right and 17 left) of 46 bronchial arteries seen at angiography were also detected at CT. All 31 bronchial arteries and sixteen (62%) of 26 nonbronchial systemic arteries causing hemoptysis were detected at CT. Twenty-three (74%) of 31 bronchial arteries causing hemoptysis were traceable from their origins to the hilum, and one (11%) of nine bronchial arteries not causing hemoptysis was traceable (P = .002)., Conclusion: Sixteen-detector row CT provides depiction and traceability of the bronchial arteries in patients with hemoptysis, and in most patients it enables detection of the bronchial and nonbronchial arteries causing hemoptysis., ((c) RSNA, 2004.)

Purpose: To examine the combined effects of monitor luminance and ambient light on observer performance for detecting abnormalities in a soft-copy interpretation of digital chest radiographs., Materials and Methods: A total of 254 digital chest radiographs were displayed on a high-resolution cathode ray tube monitor at three luminance levels (25, 50, and 100 foot-lamberts) under three ambient light levels (0, 50, and 460 lux). Six chest radiologists reviewed each image in nine modes of combined luminance and ambient light. The observers were allowed to adjust the window width and level of the soft-copy images. The abnormalities included nodule, pneumothorax, and interstitial disease. Observer performance was analyzed in terms of the receiver operating characteristics. The observers reported their subjective level of visual fatigue with each viewing mode. A statistical test was conducted for each of the abnormalities and for fatigue score by using repeated-measures two-way analysis of variance with an interaction., Results: The detection of nodules was the only reading that was affected by the ambient light with a statistically significant difference (P <.05). Otherwise, observer performance for detecting a nodule, pneumothorax, and interstitial disease was not significantly different in the nine-mode comparison. There was no evidence that the luminance of the monitors was related to the ambient light for any of the abnormalities. The fatigue score showed a statistically significant difference due to both the luminance and ambient light., Conclusion: When adequate window width and level are applied to soft-copy images, the primary diagnosis with chest radiographs on the monitor is unlikely to be affected under low ambient light and a monitor luminance of 25 foot-lamberts or more., (Copyright RSNA, 2004)

Purpose: To compare observer performance by using soft-copy images produced by an amorphous silicon flat-panel-detector system and a storage-phosphor system for the detection of simulated chest lesions., Materials and Methods: To test the diagnostic performance of these two systems, four types of simulated lesions (nodules, micronodules, lines, and reticular opacities) were superimposed over an anthropomorphic chest phantom. Digital chest radiographs were acquired with amorphous silicon flat-panel-detector (3-K [K = 1,000] matrix, 12 bits) and storage-phosphor radiography (4-K matrix, 10 bits). Six board-certified radiologists evaluated soft-copy images on a high-resolution video monitor (2,048 x 2,560 x 8 bits). A total of 14,400 observations were analyzed in terms of receiver operating characteristics., Results: Average performance in terms of nodule detection was significantly better (P <.05) with the flat-panel-detector system than with the storage-phosphor system. For micronodules, lines, and reticular opacities, no significant detection differences in averaged performance were found between the two detector systems., Conclusion: In the evaluation of soft-copy images, the amorphous silicon detector system appears to be superior to the storage-phosphor system for the detection of pulmonary nodules.

Purpose: To evaluate the causes for localized fat collection that seemed to be within the subdiaphragmatic inferior vena cava (IVC) on axial computed tomographic (CT) scans., Materials and Methods: Six consecutive patients with presumed intracaval fat collection at routine abdominal CT (n = 2) or thin-section CT of the lung (n = 4) were studied prospectively with helical CT. Three patients had chronic liver diseases. Multi-directional, two-dimensional, reformatted images were obtained from the helical CT data for identification of the relation between the IVC and fat collection. Six patients without intracaval fat collection were studied as control subjects., Results: On axial CT scans, the fat collection had a round or oval shape (in four of six patients) and was located posteromedial to the IVC (in four of six patients). On coronal reformatted images, the fat collection was outside the IVC between the diaphragm and subdiaphragmatic IVC, which was contiguous to the fat around the subdiaphragmatic esophagus. In the fat collection group, the IVC angled toward the right and narrowed to half in diameter as it passed down to the diaphragm. In the control group, the IVC was straight, although the diameter decreased similarly., Conclusion: A localized fat collection adjacent to the subdiaphragmatic IVC that mimics intracaval fat on axial CT scans is due to acute angulation of the IVC, which is probably a result of anatomic variation, chronic liver disease, or both.