Liver Tumors

Although the spatial resolution on a sonographic exam allows for the identification of very tiny lesions (2- to 3-mm in diameter), detection of a tumor on a liver examination may often be limited by an inherent lack of contrast between the tumor and the background liver such that the lesion is not appreciated or underestimated in terms of its extent and size.^{6, 7} Detection of hepatocellular carcinoma (HCC) in the cirrhotic liver is particularly difficult.⁶ The addition of contrast agents to a liver examination alters lesional contrast such that smaller and more lesions may be detected than on baseline scan alone. This has now been successfully performed with both first- and second-generation contrast agents. Levovist (Schering, Berlin, Germany), a simple air-containing first-generation agent has a liver-specific postvascular phase where the microbubbles persist within the normal liver parenchyma following clearance of the microbubbles from the vascular pool. A high MI sweep through the liver, performed 3 to 4 min following intravenous injection, will produce bright enhancement of the normal liver as the persistent contrast agent is disrupted by the ultrasonography scan. Malignant lesions including all metastases and the majority of hepatocellular carcinomas will not enhance and thereby show increased conspicuity (Figure 36g-2). A multicenter trial evaluating 150 patients with liver metastases showed increased detection of liver metastases over baseline or unenhanced scan alone.⁸ Detection of metastases was equivalent to CT scan.

Figure 36g-2

Improved detection of liver tumor with contrast-enhanced sonography. A, A sagittal sonogram shows a relatively homogenous liver parenchyma. B, A postvascular Levovist scan shows enhancement of the liver parenchyma. Tumor deposits are now clearly seen. (more...)

More recently, second-generation perfluoropropane agents such as Definity (Bristol-Myers Squibb, Bellerica, MA) are available for ultrasonography use and have further improved the ability to detect liver tumors with ultrasonography. In patients with metastases and, more importantly, in patients screened for hepatocellular carcinoma, low MI nondestructive imaging allows for both arterial and portal venous phase evaluation of the liver. Hypervascular masses such as HCC will enhance brightly and show increased conspicuity in the arterial phase. HCC will show washout in the portal phase and will then show as a nonenhanced void within the enhanced liver. By comparison, hypovascular lesions, which include most metastases, will show as a negative void in both the arterial and the portal venous phases. The addition of these contrast agents for liver study holds great promise in the future and may ultimately play a role in the detection of HCC, in particular. In North America, where CT scan is so firmly established for the detection of metastatic liver disease, it is doubtful that routine sonographic study with contrast agents will ever be performed as a regular procedure for detection of metastases.

Characterization of a liver mass is another major role of liver imaging. Grayscale sonography alone may show many features that suggest the correct noninvasive diagnosis of a mass (Figure 36g-3). Lesional vascularity, however, has proven to be the mainstay of liver mass diagnosis and contrast-enhanced CT and/or MRI scan are performed routinely for characterization of liver lesions. From knowledge of tumor vascularity as seen on angiography and more recently on CT/MRI scans, algorithms can be developed for diagnosis of liver masses based on pattern recognition. Ultrasonography with conventional Doppler alone is unable to consistently provide this vascular information. The addition of microbubble contrast agents has totally changed this potential.⁹ We have shown lesional vascularity and enhancement highly concordant with contrast-enhanced CT and MRI scan for the characterization of liver masses (see Figure 36g-1).^10–12

Figure 36g-3

Metastatic liver mass shown on a routine follow-up evaluation 1 year following colon resection for carcinoma. Transverse sonogram shows a highly echogenic and shadowing mass (arrows) with a hypoechoic rim, a classic appearance for a calcium-containing (more...)

In patients with hepatocellular carcinoma, sonography with Doppler is excellent for the demonstration of tumor thrombi in the liver vasculature and for showing neovascularity within the thrombi for differentiation of malignant from bland thrombosis. Ultrasonography is also excellent for staging liver neoplasms prior to resection. The multiplanar capability allows for demonstration of the relationship of the tumor to the liver vasculature and for determination of the segmental involvement.

The Biliary Tract

The gallbladder and the biliary ducts are both important sites of neoplasia and their evaluation is difficult on all imaging modalities. Jaundice, a frequent presenting symptom for patients with neoplastic disease in this area, is optimally studied with sonography. Objectives on the imaging study include the determination of the presence of biliary obstruction, and if present, the level of the obstruction and also the cause. In patients with obstruction, ultrasonography is highly accurate at predicting the presence and level of obstruction, although there is variability regarding the ability of ultrasonography to determine the cause. It is our belief that meticulous ultrasonography technique allows for good determination of the cause as well.^13–16

In patients with hilar biliary obstruction, we have found that the addition of postvascular scans of the porta hepatis of the liver with Levovist greatly improves the ability of sonography to differentiate benign from malignant disease and see an obstructing mass and also to determine the extent of disease.¹⁷ Tumor both within the biliary ducts and invading into the liver is nonenhancing and hence shows increased conspicuity relative to the enhanced liver parenchyma. We have shown increased tumor conspicuity in 50 patients, and further extent of disease in the majority of patients (Figure 36g-4).¹⁷

Figure 36g-4

Improved detection of tumor mass with postvascular Levovist scanning in patient with hilar cholangiocarcinoma. Left image (A) is a transverse sonogram taken at baseline showing dilated segmental right intrahepatic biliary ducts which terminate abruptly (more...)

The Kidney

Renal cell carcinoma (RCC) is a frequent incidental observation on a cross-sectional imaging study performed for an unrelated cause. The natural history of these tumors suggests that a solid renal mass that represents RCC may not grow significantly or metastasize over many years of observation. It is the demonstration of vascularity in a solid renal mass or within the nodules or septations of a complex mass that is the basis for the recommendation for resection of a renal lesion. Because of the high likelihood that vascular lesions will be malignant, resection rather than biopsy is the management rule.

Although ultrasonography may and does detect many tumors in the kidney, contrast-enhanced CT scan is regarded by most as the essential element in the work-up of a patient with hematuria, symptoms referable to the kidney, or a known kidney mass. Currently under investigation is the potential role for ultrasonography with microbubble contrast agents in the characterization of indeterminate lesions on contrast-enhanced CT scan.

Ultrasonography is an excellent accompaniment to contrast-enhanced CT in the preoperative evaluation of the patient with a renal cell carcinoma. Invasion of the renal veins with tumor extension into the inferior vena cava and even into the right atrium may be well shown on sonogram. Furthermore, detection of arterial signals within the tumor thrombi is confirmatory of malignant thrombosis.

The Pancreas

The pancreas may be involved with primary neoplasia of the exocrine and endocrine components of the gland, which creates a variety of sonographic appearances representative of the spectrum of neoplasia. Medical imaging studies are focused on lesion detection, diagnosis, and staging of disease. Sonography is an excellent modality for evaluation of all aspects of imaging of these tumors,¹⁸ and when used in conjunction with color and spectral Doppler, ultrasonography reliably predicts unresectability of pancreatic cancer on the basis of vascular involvement, lymphadenopathy, and liver metastases.^{19, 20} As with other imaging modalities, prediction of resectability is less reliable predominantly regarding microscopic tumor deposits in normal-sized lymph nodes.

The Spleen

The detection of focal splenic lesions and of splenomegaly may be a reflection of tumor involvement of the spleen. Lymphoma constitutes the most common neoplastic lesion in this organ, and may be primary in the spleen, or involve the spleen as part of multicentric disease. Lymphadenopathy is frequently associated and careful assessment of the retroperitoneum should be part of every imaging scan. Secondary tumors may also involve the spleen although with less frequency than involvement of the liver.

The Hollow Viscera

Sonographic evaluation of the gut may be performed with the use of conventional transducers placed on the abdominal wall. Conversely, endoscopic sonography, performed with high-frequency ultrasonography transducers, coupled with an endoscope, provides high-resolution evaluation of both the stomach and gut wall, as well as adjacent structures such as the pancreas and distal bile duct. Esophageal and gastric cancer, in particular, are frequently staged with the use of endoscopic sonography to evaluate for the depth of penetration through the gut wall and the presence of lymphadenopathy. The gut wall layers are shown clearly with sonography; consequently, the depth of penetration of neoplastic lesions can be predicted with a high level of accuracy.²¹ Rectal cancer, by comparison, is optimally staged with the use of a rigid intracavitary probe placed in the rectum.²² Currently, transrectal ultrasonography is the modality of choice for accurate determination of tumor invasion and the presence of regional adenopathy. Several recent publications have found transrectal ultrasonography to be superior to CT and other imaging modalities, both for preoperative staging and for follow-up of rectal cancer, with accuracy of endorectal ultrasonography for predicting depth of invasion in the 81% to 92% range.²³ The data derived bear directly on avoidance of abdominoperineal resection. Furthermore, it allows for the appropriate selection of patients with locally invasive disease who would benefit from adjuvant chemoradiation prior to surgery. Additionally, submucosal lesions and local adenopathy can be identified.

Conventional sonograms are not routinely performed for the detection of gut neoplasia although frequently a gut-related tumor may be detected on a sonographic study. In any situation where there is gross pathology, ultrasonography will usually detect the abnormality. Gut wall thickening and gut wall masses may be associated with primary and secondary tumors of the gut.

The Peritoneum

The peritoneum is frequently a site of secondary malignancy and is less commonly involved as a site of primary neoplasia. Ovarian cancer and tumors of the gastrointestinal tract and pancreas are frequent primary sources in patients with disseminated peritoneal disease. The peritoneum and the peritoneal cavity may be well assessed with sonography, although more commonly, in clinical practice, patients will be referred for CT or MRI scan if peritoneal disease is suspect. We feel that this is related to lack of awareness of the familiar appearances of peritoneal disease on sonography.²⁴ Furthermore, a sonographic study must be tailored to achieve a high accuracy in the detection of peritoneal disease. As many patients with ovarian cancer do have sonography, we recommend inclusion of the peritoneal cavity in the sonographic study.

Sonography is highly sensitive to the detection of even trace amounts of free intraperitoneal fluid. In addition to the quantitative assessment of ascites, sonography may provide a rough qualitative assessment as well. Particulate ascites has an association with blood, pus, and inflammatory cells in the peritoneal fluid and its discovery should be correlated with the clinical situation.

Peritoneal carcinomatosis shows omental caking, and tumor deposits involving any of the visceral or parietal peritoneal surfaces (Figure 36g-5). The dependent pelvic pouch is optimally studied in women with transvaginal sonography where high frequency probes may detect even tiny peritoneal seeds. Confirmation of blood flow in any tumor deposit supports an initial impression of neoplasia. All patients at risk for peritoneal malignancy should have a survey of the peritoneal cavity to include the region of the mesentery, the omentum, the diaphragmatic surfaces, both paracolic gutters, and the pelvic pouch.

Figure 36g-5

Peritoneal carcinomatosis in a patient with ovarian carcinoma. Transverse sonogram in the upper abdomen shows large, volume-free intraperitoneal fluid. A visceral peritoneal seed (arrow) is seen on the surface of the liver.