Gastroenterology and Hepatology Board Review: Pearls of Wisdom, Third Edition
Section IX MISCELLANEOUS TOPICS
CHAPTER 61. Gastrointestinal and Liver Radiology
Andrew D. Hardie, MD, Matthew Stephenson, MD, and David G. Koch, MD
What are the primary diagnostic considerations for this liver lesion as seen on magnetic resonance imaging (MRI)?
Focal nodular hyperplasia (FNH) or hepatic adenoma. FNH is usually seen as a multilobulated mass, which must be uniformly hypervascular/hyperenhancing to the liver on imaging during the “arterial phase” of contrast administration but isovascular/isoenhancing during the “portal venous phase.” FNH also often, but not always, has a central scar, which is T2 bright and enhances progressively following contrast administration. In contrast, hepatic adenoma is often round or oval with smooth margins. It also often has arterial enhancement but can have a variable postcontrast appearance (often slightly hypoenhancing on later phases of contrast).
True/False: The availability of biliary specific MRI contrast agents has effectively made nuclear imaging studies such as the sulfur colloid scan obsolete for the differentiation of FNH from hepatic adenoma.
True. The availability of biliary specific contrast agents for MRI has markedly improved the ability to differentiate these lesions, as FNH will take up the agent while adenoma will not.
How would the bowel gas pattern in the figure shown be characterized?
The pattern is typical of a small bowel obstruction (SBO). Key elements are dilation of the proximal small bowel to greater than 3 cm with relative decompression of distal small and large bowel. Adhesions related to prior intraabdominal surgery or intraabdominal infection are the most common cause of an SBO.
In this patient with known cirrhosis, what is the likely etiology of the lesion depicted in figure below?
Hepatocellular carcinoma (HCC). This solid liver lesion has the typical arterial phase enhancement compared with the liver. Note the presence of collateral vessels near the lesser curve of the stomach and splenomegaly indicating portal hypertension.
What is the most likely diagnosis depicted in this abdominal radiograph? What would be an appropriate intervention?
The markedly dilated sigmoid colon with a “coffee bean” configuration is typical of sigmoid volvulus. Attempts to reduce the volvulus with either water soluble enema or flexible sigmoidoscopy are appropriate in the absence of free intraperitoneal air.
What is the likely etiology of this liver lesion in a patient presenting with recent onset of left lower quadrant pain and fever?
This is a typical appearance of hepatic abscesses. Note the poorly defined collection in the right lobe of the liver with an enhancing internal wall surrounded by low density edema. In this case, the etiology was related to sigmoid diverticulitis.
What is the most likely etiology of this pancreatic cystic mass?
This is a typical appearance of serous cystadenoma with features consisting of a large cystic mass with multilobulated contours. Endoscopic ultrasound with fine needle aspiration (FNA) of the cyst fluid may be confirmatory.
What is the most likely cause of the abnormal appearance of the small bowel in this 26-year-old patient with chronic intermittent abdominal pain and weight loss? What type of radiologic study was performed?
Crohn’s disease. This is a computed tomography (CT) enterography study performed using a negative oral contrast agent in the arterial phase of intravenous (IV) contrast. This technique is necessary in order to visualize the mural enhancement of the bowel wall, which is present due to active inflammation.
True/False: The finding in the figure would fall within the Milan criteria for HCC.
True. The 3.3-cm lesion in the left hepatic lobe has a typical imaging appearance of HCC on MRI (arterial phase enhancement and “wash out” of contrast on delayed imaging). For a single tumor, the Milan criteria require that the lesion be less than 5 cm. The Milan criteria are used to assess postoperative survival in patients undergoing liver transplantation for HCC. They are also the basis for applying model for end-stage liver disease (MELD) exception points to patients being placed on the transplant waiting list.
What is the relevant finding shown in this abdominal radiograph from a patient presenting with an acute abdomen? What is the presumed etiology?
There is “pneumatosis” or air within the wall of the small bowel in the left upper quadrant. Given the location and appearance of the pneumatosis combined with the clinical presentation, bowel ischemia with impending infarction is the most likely diagnosis.
What is the finding shown on this endoscopic retrograde cholangiopancreatography (ERCP) done on a patient with abdominal pain and fever 3 days after laparoscopic cholecystectomy for gallstones?
This balloon occlusion cholangiogram demonstrates a round filling defect in the cystic duct (cholelithiasis) as well as contrast extravasation from the cystic duct stump.
What is the differential diagnosis of the finding on this CT of the abdomen?
Carcinoid tumor versus sclerosing mesenteritis. There is a partially calcified mass in the small bowel mesentery with stellate (star-like) borders. This is a case of carcinoid tumor and this lesion actually represents the first site of spread of carcinoid tumor of the small bowel to mesenteric nodes. The primary tumor is usually in the small bowel lumen but is rarely identified by imaging. Sclerosing mesenteritis is a poorly understood inflammatory condition of the mesentery that can have a virtually identical appearance as carcinoid.
What is the abnormal finding of the liver shown in the figure in this patient with chronically elevated aminotransferase levels taking a statin-based medication for hyperlipidemia?
Hepatic steatosis. The liver is abnormally low in density on contrast-enhanced CT in comparison with the spleen. The normal liver should be similar in density to the spleen on both noncontrast and contrast-enhanced CT. Density on CT is measured in Hounsfield units (HU).
What laboratory abnormalities would be expected for the patient with acute abdominal pain and the CT findings shown?
Elevated amylase and lipase. This is a typical CT appearance of acute pancreatitis, with edema of the pancreas and retroperitoneum. Furthermore, the lack of enhancement of portions of the pancreatic parenchyma indicates the presence of pancreatic necrosis.
What is the finding shown in the figure from a patient following colonoscopy?
Free intraperitoneal air. The patient likely has a perforated colon. Prompt surgical consultation is indicated.
What is the difference between T1 weighting and T2 weighting in MRI?
Images in MRI are possible because of the inherent differences in resonance frequencies of protons (hydrogen nuclei) in tissues under the influence of a powerful magnet. By emitting radiofrequency pulses, which excite the protons, numerous types of images can be created based on the variable relaxation of the excited protons. The degree to which a series of radiofrequency pulses (sequence) highlights the proton relaxation in the longitudinal plane (T1) or transverse plane (T2) determines whether the image is predominantly T1 or T2 weighted. Fluid in pure T1 weighted images is dark, but is bright on pure T2 weighted images. Fat is bright on both T1 and T2 weighted images, although fat saturation techniques are often employed on either. Most organs have characteristic intermediate signal characteristics on both sequences.
True/False: IV contrast for CT is contraindicated in patients with acute or chronic renal failure.
True, usually. CT contrast agents contain high quantities of iodine, which can precipitate worsening renal failure in patients with already compromised renal function. However, in patients with end-stage renal disease (ESRD) on chronic dialysis, IV contrast can be used as long as there is no chance for recovery of renal function.
What is the radiological sign depicted in the colon on this abdominal radiograph? What is a typical etiology for the finding on this CT of the abdomen?
Thumbprinting. The haustral folds in the colon (particularly transverse) are markedly thickened in this patient with colitis, becoming as wide as a thumb. The CT demonstrates the same finding in better detail. Especially in an inpatient setting, Clostridium difficile is a common etiology.
What is the radiological sign depicted on this CT of the abdomen in a patient with jaundice? What are the potential etiologies?
Double duct sign. The pancreatic duct is abnormally dilated as is the common bile duct. This indicates an obstruction in the pancreatic head or ampullary region where the ducts converge. Etiologies include adenocarcinoma of the pancreas or cholangiocarcinoma of the distal common bile duct, obstructing stone(s) near the ampulla, or an ampullary adenoma/adenocarcinoma.
What is the liver lesion depicted on this CT of the abdomen?
Hemangioma (aka, cavernous hemangioma). This benign neoplasm of capillary origin appears near fluid density prior to contrast. Following contrast, there is a typical “peripheral discontinuous nodular” enhancement pattern. Also, note how the enhancing portions of the lesion match the contrast level in the aorta at all times.
What is the likely etiology of this patient’s liver dysfunction based on this MRI?
Budd–Chiari syndrome. There is abnormal signal and enhancement of the liver parenchyma that is confined to the periphery, while the liver parenchyma surrounding the inferior vena cava (IVC) and caudate lobe enhances normally. This phenomenon is due to the fact that the latter mentioned portions of the liver can drain through the IVC and not the hepatic veins, which are obstructed.
Based on the findings in this figure, what is the likely etiology of jaundice in this patient?
Cholangiocarcinoma. There is severe biliary obstruction of the right and left hepatic lobe biliary system from an ill-defined mass. Other findings suggestive of cholangiocarcinoma are punctate calcifications on noncontrast CT and an infiltrative appearance on MRI. When occurring at the confluence of the right and left hepatic ducts, this type of tumor is referred to as a Klatskin tumor.
True/False: IV contrast agents for MRI are safe in patients with renal failure.
False. Gadolinium (a rare earth metal) is used to achieve contrast in MRI studies. In patients with normal renal function, it is rapidly cleared and poses no health risks; however, in patients with severely compromised renal function, gadolinium has been discovered to deposit in tissues and lead to a condition called nephrogenic systemic fibrosis (NSF), which can be debilitating or even fatal. Gadolinium use is absolutely contraindicated in patients with ESRD.
When might MRI be preferred to CT for evaluating a pancreatic mass?
In general, MRI better visualizes fluid containing ductal structures and better characterizes cystic lesions than CT. Hence, MRI is the test of choice for evaluating intraductal papillary mucinous neoplasm (IPMN), which arises from the pancreatic duct. It also is more often definitive for differentiating pseudocysts, serous cystadenomas, and mucinous cystadenomas/carcinomas than CT. However, CT can often more easily discern abnormalities that require fine detail, such as the local spread of pancreatic adenocarcinomas into the retroperitoneal fat and around vascular structures. However, even in this case, MRI can be superior to CT at definitely characterizing liver lesions, adrenal nodules, and lymphadenopathy, which may be essential in deciding final treatment options.
What is the likely etiology of the mass lesions in the liver seen in this patient with recent onset of constipation?
Metastatic disease from colorectal cancer. Although uncommon, colorectal metastases can have internal calcifications as is evident on this abdominal CT scan. Other adenocarcinomas, such as gastric carcinoma, can also calcify, but are less common.
What are the inherent advantages and disadvantages of small bowel follow-thru, CT enterography, and MR enterography?
Small bowel follow-thru:
Advantages: readily accessible, cheap, ability to see functional aspect of bowel
Disadvantages: long examination time (3 hours), high radiation (particularly for young patients needing serial imaging), variable interpretations, no ability to see extraluminal complications
Advantages: accessible (can be performed on most CT scanners), rapid to perform (seconds), usually a consistent technique, moderately expensive, identifies extraluminal complications, anatomy recognizable to clinicians
Disadvantages: high radiation (particularly for young patients needing serial imaging), no functional information as it is only a single “snapshot,” difficult to characterize bowel disease as acute or chronic inflammation and therefore may not be clear how to best treat
Advantages: no radiation, combines functional and anatomic information as well as allowing for rapidly advancing newer MRI techniques, probably the best method to characterize bowel disease in order to decide how best to treat
Disadvantages: less accessible, takes 30–40 minutes to perform, not always a consistent technique, expensive, less recognizable to clinicians
True/False: Based on the Milan criteria, a patient with three HCC tumors is potentially eligible for transplantation.
True. For patients with more than one tumor: a) there can be no more than three lesions, b) the largest tumor must be less than 3 cm in size, and c) the aggregate of the tumor sizes must be less than 6 cm. If all three criteria are met, then the patient would have acceptable survival with liver transplantation and may be eligible for MELD exception points when being placed on the transplant waiting list.
True/False: CT is the preferred choice for visualizing and diagnosing esophageal diseases.
False. Despite advances in CT and MRI technology, esophageal pathology is still best imaged by fluoroscopy. Not only does fluoroscopy allow for functional assessment of esophageal motility and strictures, it is much more sensitive to mucosal abnormalities than any other radiologic study.
What is the significance of pancreatic necrosis as described on CT or MRI?
Depending on the size and location of the area of necrosis, its presence is associated with increased morbidity and mortality and often leads to eventual formation of pseudocysts and disruptions of the pancreatic duct. Pancreatic duct disruptions can cause fluid collections, which are unable to be resolved by catheter drainage and occasionally lead to pancreatico-pleural fistulae.
What are the reasons to consider CT (aka, “virtual”) colonography among the choices for colon cancer screening?
In experienced hands, CT colonography (CTC) has a sensitivity approaching that of traditional optical colonoscopy for polyps greater than 1 cm in size; the lesions that are at greatest risk for progressing to cancer. As sedation is not required, CTC may be preferred for some patients. Although still requiring evacuation of feces and rectal air insufflation, some patients prefer CTC due to a lower risk of complications; hence, they may be more likely to get screened.
True/False: CTC obviates the need for conventional colonoscopy.
False. The main disadvantage of CTC is that it does not allow lesions identified to be biopsied or removed, which still requires conventional optical colonoscopy.
• • • SUGGESTED READINGS • • •
Ros PR, Koenraad JM, Pelsser V, Lee S. CT and MRI of the Abdomen and Pelvis: A Teaching File. 2nd ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2007.
Johnson CD, Schmit GD. Mayo Clinic Gastrointestinal Imaging Review. Rochester, MN: Mayo Clinic Scientific Press; 2005.
Halpert RD. Case Review Series: Gastrointestinal Imaging. Philadelphia, PA: Mosby/Elsevier; 2007.