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.

Microvessel invasion is a major prognostic factor in hepatocellular carcinoma (HCC) that influences the suitability of surgery, but rarely can be evaluated preoperatively. This study was performed to identify preoperative MRI findings that reflect histopathological microvessel invasion in hepatocellular carcinoma. Gadobenate dimeglumine-enhanced four-arterial phase dynamic study and hepatobiliary phase images of preoperative MRI of 70 HCC lesions were retrospectively reviewed. Tumor size (cm), peritumoral enhancement, tumor margins, and radiological capsule were analyzed as radiological parameters reflecting microvessel invasion and were compared with histopathological references. The chi-square test and the independent t-test were used for univariate analysis, and a logistic regression analysis was performed for multivariate analysis. In univariate analysis, tumor size (p = 0.030), peritumoral enhancement (p < 0.001), and tumor margins (p = 0.007) were associated with microvessel tumor invasion. However, in multivariate analysis irregular circumferential peritumoral enhancement only showed statistical significance (odds ratio 13.0), suggesting a high probability of microvessel invasion of HCC. Irregular circumferential peritumoral enhancement on contrast-enhanced multi-arterial phase dynamic MRI could be a preoperative surrogate marker for microvessel tumor invasion.

Solid pseudopapillary tumor of the pancreas is a rare neoplasm usually found in young women. Typical solid pseudopapillary tumor is characterized by a well-encapsulated mass with varying amounts of intratumoral hemorrhage. However, the tumor can have an atypical appearance, such as metastasis, ductal obstruction, parenchymal and extracapsular invasion, simulation of islet cell tumor, intratumoral calcification, and occurrence in a male patient. The typical and atypical manifestations of solid pseudopapillary tumor can be visualized with cross-sectional imaging.

In the field of contrast-enhanced ultrasonography (US), contrast agents are classified as either first- or second-generation agents depending on the gas within the microbubbles. In the case of first-generation contrast agents, a high-mechanical-index technique is used and only intermittent scanning is possible due to the early destruction of the microbubbles during the scanning. The use of second-generation contrast agents in a low-mechanical-index technique enables continuous scanning. Besides the detection and characterization of focal liver lesions, contrastenhanced US is helpful in the monitoring of radiofrequency ablation therapy and in the targeting step of an US-guided biopsy. Recently, there has been a demand for new criteria to evaluate the treatment response obtained using anti-angiogenic agents because morphologic criteria alone may not reflect the treatment response of the tumor and contrast-enhanced US can provide quantitative markers of tissue perfusion. In spite of the concerns related to its cost-effectiveness, contrast-enhanced US has the potential to be more widely used as a complimentary tool or to substitute the current imaging modalities in some occasions.

Stomach cancer is one of the leading causes of cancer mortality worldwide. Complete resection of a gastric tumor and adjacent lymph nodes represents the only potentially curative intervention. Computed tomography (CT) has remained the modality of choice for the preoperative staging of gastric cancer and for follow-up. A recently developed advanced CT technique that makes use of thin sections, optimal contrast material enhancement, and multiplanar reformation allows more accurate staging. However, CT may be limited in the identification of nonenlarged lymph node metastasis, peritoneal dissemination, and small hematogenous metastasis. Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) has been recognized as a useful diagnostic technique in clinical oncology. FDG PET allows scanning of a larger volume than is possible with CT. Although FDG PET is not an appropriate first-line diagnostic procedure in the detection of stomach cancer and is not helpful in tumor staging, it may play a valuable role in the detection of distant metastases, such as those of the liver, lungs, adrenal glands, ovaries, and skeleton. FDG PET may also be helpful in the follow-up of patients undergoing chemotherapy, as it allows the identification of early response to treatment. Further studies are needed to determine the efficacy of FDG PET in the detection of local nodal metastases and peritoneal dissemination. Nevertheless, the combined use of CT and PET can be helpful in the preoperative staging of stomach cancer and in the therapeutic monitoring of affected patients.