Benign liver lesions: differentiation by magnetic resonance

Liver lesions discovered incidentally on ultrasound: evaluation of reader ability to characterize lesions on MRI without intravenous contrast

RATIONALE AND OBJECTIVES

Liver lesions incidentally discovered on ultrasound (US) are often further evaluated with magnetic resonance imaging (MRI). The purpose of this study is to evaluate the added effectiveness of contrast-enhanced MRI, compared to noncontrast MRI, to correctly guide management of liver lesions incidentally identified on ultrasound in patients with low pretest probability of malignancy. We conducted the evaluation using a multireader study.

MATERIALS AND METHODS

Liver MRI studies ordered to evaluate incidental liver US lesions were selected for analysis. Patients with no prior history of cancer or chronic liver disease who had 2 years of clinical follow-up (72 patients) were selected to ensure low pretest probability of malignancy and adequate follow-up to establish proof of diagnosis. Fifty of these studies were randomly selected and analyzed by two abdominal radiologists. In the initial interpretation session, only nonenhanced images were reviewed; after 6 weeks, the complete exam including the contrast enhanced images were viewed. Differences in interpretation between the noncontrast and contrast enhanced reading sessions were assessed.

RESULTS

Sixty-nine patients (95.8%) had no abnormalities, benign masses, or hepatic steatosis accounting for the ultrasound findings. One patient was newly diagnosed with hereditary hemochromatosis, and 2 patients were newly diagnosed with metastatic disease. The most likely diagnosis changed for 15 of the lesions described by reader A, and 16 by reader B. The majority of these changes (26/31 lesions, 84%) were from one benign entity to another. Five of 31 (16%) of the changes involved that of a benign entity to a malignant one. Reader A recommended additional contrast enhanced imaging in 13/50 (26%) patients; reader B, 9/50 (18%) patients. After viewing the nonenhanced images, both readers recommended that all patients with eventual malignancies return for contrast administration and/or biopsy. After viewing the contrast-enhanced imaging, both readers accurately diagnosed all malignancies. Patient-based analysis receiver operating characteristic curves demonstrated no significant difference between the enhanced and noncontrast limbs of the study, and no significant difference between readers.

CONCLUSION

Most of the changes in lesion detection and characterization made after contrast administration were clinically insignificant. In the lesions in which clinically important differences were made, both radiologists recommended additional imaging or biopsy that would have eventually led to the correct diagnosis. None of the patients with malignancy was categorized as completely benign either on noncontrast or contrast-enhanced imaging. This supports the utility of initially performing a noncontrast examination in a population with a low pretest probability of malignancy, especially those in whom gadolinium administration is contraindicated.

Abdominal MRI advances in the detection of liver tumours and characterisation

With recent technical advances in hardware, software, and intravenous contrast agents, MRI has evolved into a clinically useful procedure to detect and characterise liver tumours. The combination of MRI systems with larger gradients, improved surface coils, and parallel imaging techniques have produced substantial improvements in MRI quality and speed of image acquisition. Images that previously needed several minutes to acquire can now be obtained in several seconds. The notably faster imaging capabilities of new MRI scanners are ideally suited for dynamic contrast-enhanced liver imaging in which early arterial-phase imaging is best for detecting hepatocellular carcinomas and hypervascular liver metastases. The inherent excellent soft-tissue contrast of MRI can be further improved by non-specific extracellular contrast agents and by liver-specific contrast agents. These contrast agents are now routinely used for liver imaging and improve the sensitivity and specificity of hepatobiliary MRI.

Evaluation of nonmalignant liver masses

Nonmalignant liver masses are increasingly being recognized with the widespread use of imaging modalities such as ultrasonography, computed tomography, and magnetic resonance imaging. The majority of these lesions are detected incidentally in asymptomatic patients. Based on the radiologic appearance, benign lesions can be categorized as solid or cystic, single or multiple, hypervascular or hypovascular. Based on histologic characteristics, they are classified as of hepatocellular, biliary, or mesenchymal origin. In the majority of patients, a proper diagnosis can be made based on these characteristics on imaging modalities alone. An invasive approach is seldom required. This review discusses the various characteristics of the most common benign liver lesions and recommends a practical approach.

Quantitative dynamic contrast-enhanced sonography of hepatic tumors

Liver tumors are defined using quantitative dynamic contrast-enhanced ultrasound compared to histological diagnosis, respectively, long-term follow-ups. Forty-two focal liver lesions in 39 patients were examined by contrast harmonic imaging over a period of 2 min after bolus injection of 10-ml galactose-based contrast agent. Vascular enhancement was quantified by using a dedicated software that allowed us to place representative regions of interest (ROI) in the center of the lesion, in the complete lesion, in regular liver parenchyma and in representative liver vessels (artery, vein and portal vein). Peak enhancement was judged to be either in the arterial, portal venous or in the late phase of liver perfusion. The lesion was described as hypovascular, isovascular and hypervascular compared to liver parenchyma. Contrast uptake was described as centrifugal or centripetal and peripheral or homogenous, respectively. Characterization of the lesions was performed unenhanced and after contrast by four independent specialists unaware of histology. Diagnosis of malignancy was evaluated by using a receiver operating characteristic (ROC) analysis, also overall accuracy, average sensitivity, specificity and negative and positive predictive values were calculated. Interobserver agreement was defined by the Kappa statistics. Histologic examination revealed 29 malignant [hepatocellular carcinoma (HCC), n=11; cholangiocellular carcinoma (CCC), n=1; lymphoma, n=1; metastases, n=16)] and 7 benign [hemangioma, n=1; focal nodular hyperplasia (FNH), n=4, adenoma, n=2)] lesions. Six benign lesions (hemangioma n=1; FNH n=5) were proved by long-term follow-up. ROC analysis regarding the diagnosis of malignancy showed values from 0.43 to 0.62 (mean 0.57) before and from 0.70 to 0.80 (mean 0.75) after contrast agent, respectively. The average values for sensitivity, specificity, accuracy and negative and positive predictive values were 66, 26, 62, 45 and 73% unenhanced and 83, 49, 73, 65 and 82% after contrast, respectively. The interobserver agreement was 0.54 and 0.65 for unenhanced and enhanced examinations, respectively. Quantitative dynamic contrast-enhanced sonography improves the diagnosis of malignancy in liver lesions.

Liver tumors: MR imaging of radioactive holmium microspheres--phantom and rabbit study

PURPOSE

To investigate the use of magnetic resonance (MR) imaging in the administration and biodistribution of holmium-loaded poly(L-lactic acid) microspheres (Ho-PLLA-MS) in liver tumors.

MATERIALS AND METHODS

MR imaging measurements were obtained in phantoms, three ex vivo rabbit livers, and four livers in living rabbits. When applicable, measurements were compared with those on scintigraphic images. The transverse relaxivity R2* of the Ho-PLLA-MS was determined in a phantom study. The in vivo animal experiments were performed by using rabbits with an implanted VX2 tumor. Detection of passing Ho-PLLA-MS to estimate lung shunting was performed in a scaled model of the vena cava.

RESULTS

In the ex vivo liver experiments, the feasibility of real-time MR imaging during administration of microspheres was demonstrated. The in vivo rabbit experiments demonstrated that MR imaging can depict radioactive, nonradioactive, and decayed Ho-PLLA-MS after treatment for as long as they remain in the body. Furthermore, this study showed the ability of dynamic MR imaging to detect single doses of passing Ho-PLLA-MS.

CONCLUSION

Ho-PLLA-MS used for internal radionuclide therapy can be imaged clearly in vivo with MR imaging.

A liver tumour as an incidental finding: differential diagnosis and treatment

BACKGROUND

A liver tumour is occasionally found by coincidence during upper abdominal imaging. The diagnostic and therapeutic strategy for incidental liver tumours is discussed.

METHODS

Review of the literature.

RESULTS

When a liver tumour is found by coincidence, the questions to be answered are whether a definite diagnosis can be reached by imaging alone, and whether treatment is indicated. To answer the first question we have to know the characteristics of the various liver tumours with different imaging techniques, and the added value of more invasive diagnostic procedures. For an answer to the second question, information on the natural course of the specific tumour and on the risks and benefit of treatment is required. Of course, the a priori chance of certain diagnoses depends on the presence or absence of risk factors. Using simple imaging techniques, liver lesions can be categorized as single or multiple and as cystic or solid. Cystic lesions are usually benign, either congenital or parasitic. Solid lesions can be benign or malignant. The most common benign lesions are haemangioma, focal nodular hyperplasia and hepatocellular adenoma. Malignant tumours arising in the normal liver can be primary, in the form of hepatocellular carcinoma, or secondary, resulting from dissemination of a primary tumour outside the liver. All these tumour types can present with typical features in various imaging studies. A definite diagnosis based on imaging alone, however, is not always possible. On the other hand, even histological examination of biopsy samples sometimes does not differentiate between benign and malignant tumours. In the case of an asymptomatic liver tumour the main indication for treatment is proven or suspected malignancy. Large adenomas form a notable exception, these should be removed if they are over 5 cm in diameter or when they grow during follow-up, especially during pregnancy. Therapy will usually consist of liver resection, either partial or, when this is not possible, complete resection followed by liver transplantation. An important caveat is that a surgical procedure without morbidity and mortality does not exist. For symptomatic benign liver tumours the options are the same, but there may be equally effective and less risky alternatives in specific cases, such as embolization for focal nodular hyperplasia and irradiation for haemangioma.

CONCLUSION

The diagnostic and therapeutic approach to incidental liver tumours depends on several factors, including size, aspect and number of the tumours, the clinical background, the a priori chance of a certain type of tumour and especially the risk of malignancy.