Computed tomography (CT) and ultrasonography (US) are ideally suited for demonstrating urachal remnant diseases. A patent urachus is demonstrated at longitudinal US and occasionally at CT as a tubular connection between the anterosuperior aspect of the bladder and the umbilicus. An umbilical-urachal sinus manifests at US as a thickened tubular structure along the midline below the umbilicus. A vesicourachal diverticulum is usually discovered incidentally at axial CT, appearing as a midline cystic lesion just above the anterosuperior aspect of the bladder. At US, it manifests as an extraluminally protruding, fluid-filled sac that does not communicate with the umbilicus. Urachal cysts manifest at both modalities as a noncommunicating, fluid-filled cavity in the midline lower abdominal wall located just beneath the umbilicus or above the bladder. Both infected urachal cysts and urachal carcinomas commonly display increased echogenicity at US and thick-walled cystic or mixed attenuation at CT, making it difficult to differentiate between them. Percutaneous needle biopsy or fluid aspiration is usually needed for diagnosis and therapeutic planning. Nevertheless, CT and US can help identify most disease entities originating from the urachal remnant in the anterior abdominal wall. Understanding the anatomy and the imaging features of urachal remnant diseases is essential for correct diagnosis and proper management.

The peritoneum is the largest serous membrane in the body and the one with the most complex structure. The omentum is a double-layered extension of the peritoneum that connects the stomach to adjacent organs. The peritoneal reflections form the greater and lesser omenta, and the natural flow of peritoneal fluid determines the route of spread of intraperitoneal fluid and consequently of disease processes within the abdominal cavity. The omenta serve both as boundaries for disease processes and as conduits for disease spread. The omenta are frequently involved by infectious, inflammatory, neoplastic, vascular, and traumatic processes. Computed tomography (CT) is a primary diagnostic method for evaluation of omental diseases, most of which may manifest with nonspecific clinical features. Multidetector CT with multiplanar reformation allows accurate examination of the complex anatomy of the peritoneal cavity, knowledge of which is the key to understanding the pathologic processes affecting the greater and lesser omenta.

OBJECTIVE. The purpose of our study was to evaluate the abdominopelvic CT findings of various intraabdominal complications secondary to ventriculoperitoneal shunts for hydrocephalus and to review the literature.MATERIALS AND METHODS. The CT images of 70 patients (33 men and 37 women; mean age, 48.5 years) who underwent ventriculoperitoneal shunt placement and abdominopelvic CT because of shunt-related abdominal symptoms were reviewed retrospectively. CT images were analyzed with regard to the location of the shunting catheter tip; site, size, wall, and septa of localized fluid collection; peritoneal thickening; omentomesentery infiltration; abscess; bowel perforation; abdominal wall infiltration; and thickening of the catheter track wall.RESULTS. The mean period between the last ventriculoperitoneal shunting operation and CT was 11 months (range, 1 week to 115 months), and the mean number of ventriculoperitoneal shunting operations undergone was 1.4 (range, 1–6). A total of 76 ventriculoperitoneal shuntin...

In patients with rectal cancer who have received concurrent chemotherapy and radiation therapy (CCRT) before surgery, magnetic resonance (MR) imaging has low accuracy in prediction of the pathologic stage owing to overstaging or understaging. The factors related to this problem include fibrosis, desmoplastic reaction, edema, inflammation, and viable tumor nets at a fibrotic scar from a previous tumor. Preoperative diagnosis with MR imaging of histologic variants of rectal adenocarcinoma, especially mucinous adenocarcinoma, is important because these variants tend to have a poor response to CCRT. In addition, these variants manifest with high signal intensity on T2-weighted images after CCRT; this finding makes it difficult to differentiate residual tumors from remaining mucin pools. MR volumetry and functional MR imaging may be helpful in prediction and assessment of tumor response to CCRT. Awareness of post-CCRT changes helps radiologists achieve appropriate restaging of irradiated rectal cancer with MR imaging and can lead to a reduction in understaging or overstaging. It is important to obtain and compare both pre- and post-CCRT images before interpreting the post-CCRT images.

To determine the magnetic resonance (MR) imaging findings of small nontumorous hepatic arterial-portal venous (arterioportal) shunts in the liver. MR images in 25 patients with 38 small nontumorous arterioportal shunts verified with surgery or follow-up imaging were included in this study. The causes of arterioportal shunts were iatrogenic causes in 11 patients and/or cirrhotic changes in the remaining patients. Nonenhanced T1- and T2-weighted images and multiphase contrast material-enhanced dynamic images were retrospectively reviewed and compared with conventional hepatic arteriograms to determine the MR characteristics related to the focal hemodynamic changes. On arterial-dominant-phase dynamic MR images, 29 (76%) of the 38 arteriographically suggested nontumorous arterioportal shunts displayed abnormal findings distinguished against the surrounding hepatic parenchyma, including wedge-shaped (n = 14), nodular (n = 9), or irregularly outlined (n = 6) areas of focal contrast enhancement. The signal intensity on nonenhanced T1- and T2-weighted images of the corresponding areas appeared unremarkable except for three wedge-shaped high-signal-intensity areas (three [8%] of 38) on T2-weighted images accompanied by prolonged contrast enhancement. Most (24 [83%] of 29) areas of abnormal signal intensity were located at the periphery of the liver parenchyma. A small nontumorous arterioportal shunt should be considered one of the causes of focal parenchymal hyperperfusion abnormalities on contrast-enhanced dynamic MR images of the liver in the absence of abnormal signal intensity on static MR images.