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A variety of conditions may mimic hepatic malignancy at MRI. These include benign hepatic tumors and tumor-like entities such as focal nodular hyperplasia-like lesions, hepatocellular adenoma, hepatic infections, inflammatory pseudotumor, vascular entities, and in the cirrhotic liver, confluent fibrosis, and hypertrophic pseudomass. These conditions demonstrate MRI features that overlap with hepatic malignancy, and can be challenging for radiologists to diagnose accurately. In this review we discuss the MRI manifestations of various conditions that mimic hepatic malignancy, and highlight features that may allow distinction from malignancy. Level of Evidence 5 Technical Efficacy Stage 3.

Neurofibromatosis type 1 (NF1) is an autosomal dominant hereditary tumor syndrome, with a wide clinicopathologic spectrum. It is defined by characteristic central nervous system, cutaneous and osseous manifestations, and by mutations in the NF1 gene, which is involved in proliferation via p21, RAS, and MAP kinase pathways. Up to 25% of NF1 patients develop intra-abdominal neoplastic manifestations including neurogenic (commonly plexiform neurofibromas and malignant peripheral nerve sheath tumors), interstitial cells of Cajal (hyperplasia, gastrointestinal stromal tumors), neuroendocrine, and embryonal tumors (rhabdomyosarcoma). Nonspecific symptoms, multifocal disease, or coexistence of 2 or more tumor types make patients challenging to diagnose and manage. Screening for intra-abdominal tumors in NF1 patients remains controversial, and currently no guidelines are established. Management decisions are complex and often informed by single-center experiences or case studies in the literature, though the field is rapidly evolving. Thus, NF1 patients should be followed in specialist centers familiar with their wide spectrum of pathology and with multidisciplinary care including specialized pathology and radiology. This review will (1) provide a contemporaneous synthesis of the literature and our multi-institutional clinical experiences with intra-abdominal neoplasms in NF1 patients, (2) present a classification framework for this heterogeneous group of disorders, and (3) outline approaches to screening, surveillance, diagnosis, and management.

Objectives To evaluate gadoxetic acid-enhanced liver MRI (EOB-MRI) versus contrast-enhanced computed tomography (CECT) for preoperative detection of liver metastasis (LM) and reduction of open-close laparotomies for pancreatic ductal adenocarcinoma (PDAC). Methods Sixty-six patients with PDAC had undergone preoperative EOB-MRI and CECT. LM detection by EOB-MRI and CECT and their impact on surgical planning, open-close laparotomies were compared by clinical and radiology reports and retrospective analysis of imaging by two blinded independent readers. Histopathology or imaging follow-up was the reference standard. Statistical analysis was performed at patient and lesion levels with two-sided McNemar tests. Results EOB-MRI showed higher sensitivity versus CECT (71.7% [62.1-80.0] vs. 34% [25.0-43.8]; p = 0.009), comparable specificity (98.6%, [96.9-99.5] vs. 100%, [99.1-100], and higher AUROC (85.1%, [80.4-89.9] vs. 66.9%, [60.9-73.1]) for LM detection. An incremental 7.6% of patients were excluded from surgery with a potential reduction of up to 13.6% in futile open-close laparotomies due to LM detected on EOB-MRI only. Conclusions Preoperative EOB-MRI has superior diagnostic performance in detecting LM from PDAC. This better informs surgical eligibility with potential reduction of futile open-close laparotomies from attempted curative intent pancreatic cancer surgery.

Background Desmoid fibromatosis (DF) is a rare fibroblastic proliferation that was historically treated with surgery. We report (a) outcomes using low‐dose chemotherapy, methotrexate (MTX), and vinorelbine (VNL) for patients with progressing disease (PD) and (b) whether tumor volume (V tumor) and T2 signal on magnetic resonance imaging (MRI) are more reflective of treatment response compared with maximum tumor dimension (D max) defined by RECIST1.1. Methods Patients with biopsy‐proven DF, treated with MTX/VNL from 1997 to 2015 were reviewed. MRI for a subset of patients was independently re‐evaluated for response by RECIST, V tumor, and quantitative T2 hyperintensity. Results Among 48 patients treated for a median 19 months MTX/VNL, only nine (19%) had previous surgery. RECIST‐based overall response rate was complete response (CR) 20 (42%) + partial response (PR) 19 (39%), stable disease (SD) 8 (17%), for a clinical benefit rate of 98%. The median progression‐free survival (PFS) was 120 months, (95%CI 84‐155 months). Thirty‐six (75%) patients had not progressed at a median 38 months from treatment completion. Most common grade 1/2 toxicities included nausea (n = 12, 25%) and fatigue (n = 9,19%) with no grade 3/4 toxicities. In 22 patients with serial MRIs, there was a decrease in D max mean by 30%, V tumor by 76%, and in 19/22 (86%) a decrease in T2 signal intensity. Conclusion Low‐dose MTX/VNL for a defined duration has high efficacy with sustained benefit and minimal toxicity for treating DF. V tumor and T2 signal might better predict treatment response than RECIST.

Urinary diversions are surgical procedures that reconstruct the lower urinary tract following cystectomy. The 2 common surgical approaches are based on the continence status of the urinary tract. Incontinent diversions have continuous urine drainage through a cutaneous stoma, whereas continent diversions offer the patient the ability to self-void either via stoma catheterization or with the patient's own urethra. Given the large number of diversion procedures available, postsurgical anatomy may be complex. Multiple imaging modalities can be used to assess the postprocedural anatomy, potential complications, and for on-going oncologic monitoring. The purpose of this review is to describe the common surgical techniques and associated complications.

Acute mesenteric ischemia (AMI) is a life-threatening condition with a high mortality rate. The diagnosis of AMI is challenging because patient symptoms and laboratory test results are often nonspecific. A high degree of clinical and radiologic suspicion is required for accurate and timely diagnosis. CT angiography of the abdomen and pelvis is the first-line imaging test for suspected AMI and should be expedited. A systematic "inside-out" approach to interpreting CT angiographic images, beginning with the bowel lumen and proceeding outward to the bowel wall, mesentery, vasculature, and extraintestinal viscera, provides radiologists with a practical framework to improve detection and synthesis of imaging findings. The subtypes of AMI are arterial and venoocclusive disease, nonocclusive ischemia, and strangulating bowel obstruction; each may demonstrate specific imaging findings. Chronic mesenteric ischemia is more insidious at onset and almost always secondary to atherosclerosis. Potential pitfalls in the diagnosis of AMI include mistaking pneumatosis as a sign that is specific for AMI and not an imaging finding, misinterpretation of adynamic ileus as a benign finding, and pseudopneumatosis. Several enterocolitides can mimic AMI at CT angiography, such as inflammatory bowel disease, infections, angioedema, and radiation-induced enterocolitis. Awareness of pitfalls, conditions that mimic AMI, and potential distinguishing clinical and imaging features can assist radiologists in making an early and accurate diagnosis of AMI. ©RSNA, 2020.

The purpose of this article is to review MRI technique, relevant anatomy, and MRI classification systems for the assessment of perianal fistulising disease. We present a stepwise approach to the assessment of perianal fistulas on MRI utilizing a systematic reporting format. MRI is invaluable for the assessment of perianal fistulas. A systematic report can help communicate the anatomy of complex fistulising disease to assist with optimal management.

OBJECTIVE. The purpose of this article is to review how fat is detected on imaging and to discuss the differential diagnosis of fat-containing liver lesions. CONCLUSION. Fat is a highly useful feature in characterizing liver lesions on imaging. Although a variety of liver lesions can show fat on cross-sectional imaging, the presence of fat usually indicates that the lesion is of hepatocellular origin. Less commonly, nonhepatocellular fatty lesions may be distinguished by ancillary clinical and imaging features.

Clinical Vignette: A 50-year-old woman presents to the emergency department with increasing abdominal pain. Abdominal computed tomography imaging reveals an expanded inferior vena cava&ndash, filling defect that is suspicious for a retroperitoneal sarcoma, possibly a primary leiomyosarcoma of the inferior vena cava. The surgery team discusses the case with the radiologist, and all agree that there are multiple challenges with obtaining a tissue diagnosis and determining resectability. Thus, it is decided that this patient should be discussed at a multidisciplinary case conference.

To review borderline resectability criteria for pancreatic malignancies, show examples of few surgically treated minimally advanced pancreatic malignancies, discuss various complex vascular reconstructions, and highlight the imaging appearances. Often aggressive surgical approaches are used to treat borderline to minimally advanced pancreatic malignancies in specialist centers. As abdominal radiologists it is essential to have up-to-date knowledge to distinguish such tumors with accuracy and also be well versed with the various vascular reconstructions used in such surgeries. We will show various examples of resected borderline resectable and minimally advanced pancreatic malignancies, highlight crucial vascular involvements, describe various types of advanced vascular reconstructions, and review their standard imaging appearances. We will also briefly describe the vascular complications and highlight the importance of imaging surveillance in early post-operative period. It is essential for abdominal radiologists in specialist centers where aggressive surgical approaches are used to have accurate knowledge to assess vascular involvement in pancreatic malignancies and equally to recognize and assess vascular reconstructions on imaging after complex surgeries.

Purpose To evaluate the performance of a multiparametric (mp) MRI scoring system for assessment of tumour response in patients with locally advanced rectal cancer (LARC) after neoadjuvant chemoradiotherapy (CRT). Method Fifty-nine consecutive patients with LARC who had rectal MRI before and after CRT followed by surgery were included. Two radiologists retrospectively assessed tumour response using a proposed mpMRI scoring system. Treatment response was classified as complete, near complete, partial or poor. Accuracy, sensitivity, specificity, positive predictive value and negative predictive values were calculated and inter-reader agreements were assessed. Pathologic tumour regression grade (pTRG) was the reference standard. Results Treatment response was correctly predicted by both readers in 32.2%–40.7% of patients. Overestimation was more common than underestimation. Sensitivity, specificity, PPV and NPV for pathologic complete response (pCR) among both readers was 16.7–33.0 %, 88.7–94.2 %, 14.3–40.0 % and 92.5–94.2 % respectively. Sensitivity and PPV for both readers improved to 56.0–60.0 % and 53.6–66.7 % respectively when complete response and near complete response categories (good responders) were combined. Inter-reader agreement using the scoring system was fair (κ = 0.383). Agreement between mpMRI score and pathological tumour response was poor to fair for both readers (κ = 0.050 to 0.258) but improved when complete and near complete response categories (good responders) were combined (κ = 0.214 to 0.362). Conclusions Despite low agreement between radiological tumour response and pTRG, the proposed mpMRI-based scoring system appears useful in identifying good responders who may benefit from nonoperative management strategies.

OBJECTIVE. Myelolipoma is a benign tumor composed of fatty and hematopoietic elements. Presacral myelolipoma is rare, with fewer than 40 cases reported in the English literature. It is important to make an accurate diagnosis because there are malignant diseases included in the differential diagnosis of a presacral fatty mass, particularly liposarcoma. CONCLUSION. The combination of a well-encapsulated fat-containing presacral mass, lack of coinciding hematologic disease, and uptake on sulfur colloid scintigraphy support the diagnosis of a presacral myelolipoma.

The purpose of this article is to evaluate the diagnostic performance of MRI for detection of extramural venous invasion (EMVI) compared with histopathologic analysis using elastin stain.Forty-nine patients with rectal cancer who had undergone surgical resection with preoperative MRI were identified. Thirty-seven patients had received preoperative chemoradiation therapy (CRT). Sixty-nine MRI studies were independently reviewed by two blinded radiologists for EMVI using a score of 0-4. Comparison was made with histopathologic results obtained by two pathologists reviewing the elastin-stained slides in consensus. EMVI status was also correlated with other tumoral and prognostic features on imaging and pathologic analysis. Statistical analysis was performed using Fisher exact and McNemar tests.EMVI was present in 31% of the pathology specimens. An MRI EMVI score of 3-4 was 54% sensitive and 96% specific in detecting EMVI in veins 3 mm in diameter or larger. Inclusion of a score of 2 as positive for EMVI increased the sensitivity to 79% but decreased the specificity to 74%, with poor positive predictive value. Preoperative CRT had no significant effect on the diagnostic performance of MRI. Contrast-enhanced MRI increased reader confidence for diagnosis or exclusion of EMVI compared with T2-weighted imaging. EMVI status correlated with depth of extramural invasion and proximity to mesorectal fascia.Despite an anticipated increase in sensitivity for EMVI detection by histopathologic analysis using elastin compared with H and E staining, MRI maintains a high specificity and moderate sensitivity for the detection of EMVI.

In this article, we begin with an introduction of the perianal region anatomy, then review the definition, etiology, epidemiology, and 2 major classification systems of perianal fistulas. The role of MR imaging for assessment of perianal fistulas is mainly discussed. Finally, the medical and surgical treatment principles are reviewed.

Extramural venous invasion (EMVI) is an independent prognostic factor for prediction of overall unfavorable outcomes in rectal cancer. While EMVI has traditionally been detected in postoperative pathologic specimens, MRI can provide this important piece of information preoperatively. This article reviews the methods of EMVI detection and their clinical implications for treatment and outcomes of rectal cancer. EMVI has fundamental implications for rectal cancer prognosis and long-term outcomes. Since MRI has the advantage of preoperative detection of EMVI, it has been suggested that MRI-detected EMVI be incorporated for preoperative chemoradiotherapy (CRT) treatment stratification of rectal cancer for better patient triage and outcomes.

Although multidisciplinary cancer conferences have been reported to lead to improved patient outcomes, few studies have reported results of these for rectal cancer.The purpose of this work was to assess the quality of multidisciplinary cancer conferences, the effect of the conference on the initial treatment plan, compliance with the conference treatment recommendations, and clinical outcomes for rectal cancer.This was a prospective, longitudinal study.The study was conducted at a tertiary care academic hospital.Patients with primary rectal cancer were included in this study.The intervention was a rectal cancer-specific multidisciplinary cancer conference.The quality of the multidisciplinary cancer conference was assessed using the Cancer Care Ontario Multidisciplinary Cancer Conference standards score. A change in treatment plan was defined as a change from the initial treatment plan selected by the treating physician to an alternate treatment plan recommended at the conference.Twenty-five multidisciplinary cancer conferences were conducted over a 10-month study period. The Cancer Care Ontario Multidisciplinary Cancer Conference standards score was 7 (from a maximum score of 9). Forty-two patients with primary rectal cancer were presented, and there was a 29% (12/42) change in the initial treatment plan. A total of 42% (5/12) of these changes were attributed to reinterpretation of the MRI findings. There was 100% compliance with the conference treatment recommendations. The circumferential resection margin was positive in 5.5% (2/36).Selection bias may have led to an overestimate of effect, and there is no control group for comparison of clinical outcomes.A high-quality rectal cancer-specific multidisciplinary cancer conference led to a 29% change in the treatment plan for patients with primary rectal cancer, with almost half of these changes attributed to reinterpretation of the magnetic resonance images.

A wide variety of hepatic lesions contain fat within them in a proportion good enough to be demonstrable on imaging. With the biological behaviors quite different from each other, they form a clinico-radio-pathologic spectrum worth remembering. We present a review of common and uncommon focal hepatic lesions containing fat (micro- and macroscopic) within them and emphasize the role of imaging in their diagnosis.

Rectal cancers are the second most common GI carcinoma. Prognosis and therapeutic decisions hinge on the extent of disease. We present a comprehensive structured approach for staging rectal cancer using MRI to ensure the clear, concise, and standardized communication of disease extent to guide optimal treatment planning. MRI is crucial for local staging of rectal cancer. A standardized approach to reporting of rectal MRI focused on communication of essential treatment planning and prognostic indicators ensures maximal added value to referring physicians to guide appropriate management.

Periampullary diverticulum (PAD) often presents as an incidental CT finding. Its significance and its effect on biliary dilation are unclear. The aim of our study was to determine if the presence of a PAD is associated with abnormal dilation of the common bile duct (CBD).Patients with PAD were retrospectively identified from the radiology database from November 2011 to November 2012 and those with known pancreaticobiliary pathology were excluded, except patients with cholelithiasis and prior cholecystectomy. A total of 150 patients with PAD were selected as well as a control group of 150 patients with no PAD. Data with respect to demographics, PAD size and location, ductal diameter, previous cholecystectomy and liver function tests were collected. To compare the groups, the Student's t-test and χ(2) analysis were used where appropriate.The male : female ratio was 1 : 1.2 with a median average of 71 years in the PAD group. There was no statistical difference in the CBD measurement (at the pre-ampulla and pancreatic head, and distal to confluence) between the PAD and control groups (4.8, 6.9 and 6.8 mm for the PAD group; 4.7, 6.8 and 6.4 mm for the control group; p = 0.5, 0.7 and 0.3). Also, no difference was observed in the right and left intrahepatic biliary ducts (2.7, 2.7 mm for the PAD group; 2.5, 2.6 mm for the control group; p = 0.2, 0.6). There was a significantly higher incidence of cholecystectomy history (23% vs 8.7%, p 0.01) and cholelithiasis (22% vs 11%, p 0.01) in the PAD group, and no difference in the liver function tests. Subgroup analysis of small vs large PAD (20 mm, ≥20 mm) did not show a difference in the CBD and intrahepatic biliary duct measurements. When comparing cholecystectomy vs non-cholecystectomy groups, CBD measurements were significantly higher in the cholecystectomy group.Our study confirms that PAD on its own does not lead to abnormal CBD dilatation. However, increased incidence of cholelithiasis and cholecystectomy was noted in the presence of PAD.PAD on its own does not cause CBD dilatation.

The purpose of this study was to assess the impact of a noise reduction technique on image quality, radiation dose, and low-contrast detectability in abdominal CT for obese patients.A liver phantom with 12 different tumors was designed, and fat rings were added to mimic intermediately sized and large patients. The intermediate and large phantoms were scanned with our standard abdominal CT protocol (image noise level of 15 HU and filtered back projection [FBP]). The large phantom was scanned with five different noise levels (10, 12.5, 15, 17.5, and 20 HU). All datasets for the large phantom were reconstructed with FBP and the noise reduction technique. The image noise and the contrast-to-noise ratio (CNR) were assessed. Tumor detection was independently performed by three radiologists in a blinded fashion.The application of the noise reduction method to the large phantom decreased the measured image noise (range, -14.5% to -37.0%) and increased the CNR (range, 26.7-70.6%) compared with FBP at the same noise level (p0.001). However, noise reduction was unable to improve the sensitivity for tumor detection in the large phantom compared with FBP at the same noise level (p0.05). Applying a noise level of 15 HU, the overall sensitivity for tumor detection in the intermediate and large phantoms with FBP measured 75.5% and 87.7% and the radiation doses measured 42.0 and 23.7 mGy, respectively.Although noise reduction significantly improved the quantitative image quality in simulated large patients undergoing abdominal CT compared with FBP, no improvement was observed for low-contrast detectability.

Objective: In clinical practice, PET images are acquired during shallow breathing and CT images of the PET/ CT during shallow breathing or at near end-expiration. We determined the clinical significance of pulmonary nodules that were missed on PET/CT acquired during non-breath-hold (NBH) imaging in patients with proven non-thoracic solid malignancies. Methods: 200 consecutive cancer patients who underwent both PET/CT and diagnostic breath-hold (BH) chest CT within 30 days, and who had a follow-up with BH CT at least 2 years after these baseline studies, were evaluated. NBH CT of the PET/CT was analyzed first, followed by the baseline BH CT. Missed nodules were defined as nodules not detected on NBH PET/CT, but detected on BH CT. Missed nodules were then evaluated on BH CT performed at least 2 years later. A second radiologist was used to evaluate inter observer variability for a subset of 50 patients. Results: 343 nodules were identified in 121 patients. 166 nodules from 86 patients were classified as missed nodules. Seven of these 166 nodules were excluded due to interval surgery or development of consolidation. When a change in size was counted only if it was ≥2 mm, only 11 of the 159 nodules (6.9%) grew, 113 nodules (71.1%) did not change, and the remaining 35 nodules (22.0%) were not present at follow-up. Malignancy was deemed the most likely diagnosis in only 6 of the original 159 missed nodules. Conclusion: Although the incidence of pulmonary nodules missed on NBH PET/CT was high, most of these nodules did not show any growth on follow-up and few were proven to be metastatic. Current clinical practice of PET/CT, with acquisition during shallow breathing or at near end expiration is sufficient; performing additional deep inspiration BH CT does not appear warranted.

We report a case of an abandoned distal limb of a ventriculoperitoneal shunt that resulted in hepatic as well as colonic perforation in a 12-year-old girl. Although it is common practice at the time of shunt revision to leave a retained distal catheter in the peritoneal cavity, we suggest this can result in perforation of solid as well as hollow viscera.

Mesenteric ischaemia comprises a broad, heterogeneous group of diseases characterised by inadequate blood supply to the small or large bowel. Acute mesenteric ischaemia is a surgical emergency, with significant associated morbidity and mortality. Because the clinical presentation of mesenteric ischaemia is variable and often nonspecific, a high index of clinical and radiologic suspicion is required for early diagnosis. The severity of mesenteric ischaemia ranges from transient, localised ischaemia to frank necrosis of the bowel. The most common causes of acute mesenteric ischaemia are embolic and thrombotic occlusion of the superior mesenteric artery, whereas chronic mesenteric ischaemia is almost always associated with generalised atherosclerotic disease. Multidetector computed tomography (MDCT) angiography is the preferred imaging test for acute and chronic mesenteric ischaemia. MDCT is useful in making a prompt, more precise diagnosis of mesenteric ischaemia, as well as identifying the cause and potential complications, which are key to reducing patient morbidity and mortality. In this article, we review the clinical features and aetiologies of mesenteric ischaemia and illustrate the imaging manifestations on MDCT. • Acute and chronic mesenteric ischaemia are morbid conditions challenging to diagnose. • MDCT is the first-line imaging test for evaluating patients with suspected mesenteric ischaemia. • Bowel findings include wall thickening, abnormal enhancement, pneumatosis and luminal dilation. • Vascular occlusion, portomesenteric venous gas, mesenteric congestion and free air can be seen.