10 Part I – High-Fluid Content Liver Lesions
5 Cyst III – Multiple Small Lesions with MR-CT-US Comparison
Recent studies suggest that small (< 15 mm) liver lesions seen at computed tomography (CT) are benign in more than 80 % of patients with known malignancy. With the application of multi-row detector CT and thinner collimation, it is likely that more liver lesions will be detected that will need additional imaging for characterization, most likely with MR imaging. It is particularly important to distinguish benign from metastatic and primary malignant lesions.
Literature
1.Schwartz LH, Gandras EJ, Colangelo SM, et al. (1999) Prevalence and importance of small hepatic lesions found at CT in patients with cancer. Radiology 210:71 – 74
2.Haider MA, Amital MM, Rappaport DC, et al. (2002) Multi-detector row helical CT in preoperative assessment of small (1.5 cm) liver metastases: is thinner collimation better? Radiology 225:137 – 142
3.Hussain SM, Semelka RC (2005) Hepatic imaging: comparison of modalities. Radiol Clin N Am 43:929 – 947
MR Imaging Versus Computed Tomography and Ultrasound
The appearance and the ability to characterize small hepatic cysts differ considerably between MR imaging, CT, and US (Figs. 5.1 – 5.3). At MR imaging, hepatic cysts can be characterized based on a unique combination of findings including very bright signal on T2weighted sequences with sharp margins and absence of enhancement on all phases of dynamic gadolinium-enhanced as well as on delayed phase images. Due to large intrinsic tissue differences between the background liver (dark) and cysts (very bright), even very small cysts of only a few millimeters in diameter can be detected and characterized on images with much larger slice thickness. CT and ultrasound lack these properties, and hence the characterization of small hepatic lesions (mainly distinction between solid and non-solid lesions) may be difficult. Detection and characterization on CT is mainly based on two parameters: (1) differences in X-ray attenuation and (2) differences in enhancement. On contrastenhanced CT images, cysts appear grayish compared to the enhanced liver. On contrast-enhanced MR images, cysts appear almost as signal voids (very dark) compared to the enhanced liver. This suggests that MRI is as sensitive to gadolinium as CT is for iodine contrast media. At US, cysts appear very dark with sharp margins and increased sound transmission through the lesion, although with the application of real-time image optimization possibilities such as beam-steering, increased sound transmission may not be obvious. In addition, in many centers it is common practice to obtain confirmation of US findings at CT or MRI, especially in patients with an underlying malignancy.
Differential Diagnosis
At MR imaging, typical cysts will have no differential diagnosis. At US and CT, smaller lesions may have differential diagnosis with solid liver lesions, such as metastases.
Management
MR imaging often plays a decisive role in the management of patients with small hepatic cysts, particularly if there is an underlying malignancy.
5 Cyst III – Multiple Small Lesions with MR-CT-US Comparison 11
Fig. 5.1. Cysts, drawings. SSTSE: cysts are very bright with sharp demarcations; SSTSE: at a slightly higher anatomic level, a number of smaller subcapsular cysts (solid arrows) can be seen due to high intrinsic tissue con-
Fig. 5.2. Cysts, multiple liver and renal cysts, MRI and CT findings. A Axial T2-w SSTSE image (SSTSE): Two larger (arrows) and several smaller cysts are visible with high signal and sharp demarcation. B Axial SSTSE image (SSTSE): At a slightly higher anatomic level, a number of smaller subcapsular cysts (solid arrows) can be seen due to high intrinsic tissue contrast. One of the larger cysts shows lower signal due to partial volume (open arrow). C Axial arterial phase image (ART): One of the larger cysts shows no enhancement. D Axial delayed phase image (DEL): The cyst remains unenhanced (arrow).
trast; one of the larger cysts shows lower signal due to partial volume (open arrow); ART: smaller cysts are not visible; one of the larger cysts shows no enhancement; DEL: the larger cyst remains unenhanced
E CT in the portal phase (CT): The larger subcapsular cyst is visible with sharp margins whereas the other cyst (arrow) is not well visible due to partial volume. F CT in the portal phase at a higher level (CT): Several smaller hypodense lesions are visible („too small to be characterized“). G Axial delayed phase image (DEL): The cyst with the partial volume on CT is well visible with sharp demarcation (arrow). H Coronal SSTSE image (SSTSE): Note multiple hepatic as well as bilateral renal cysts are also present
Fig. 5.3. Cyst, US, CT, and MRI findings. A Ultrasound (US) shows a typical hepatic cyst with sharp margins and increased sound transmission through the lesion (arrows), indicating its non-solid nature. B Computer tomography after contrast in the portal phase (CT) shows an unenhanced cyst with
sharp margins. C A strongly T2-weighted SSTSE image (MR-T2) shows the cyst as a very bright lesion. D T1-weighted image after contrast in the delayed phase GRE (MR-DEL) shows the unenhanced cyst. Note that the cyst appears much darker compared to the liver than on the CT image
12 Part I – High-Fluid Content Liver Lesions
6 Cyst IV – Adult Polycystic Liver Disease
One of the most common extrarenal manifestations of adult polycystic kidney disease (APKD) is hepatic cysts, which occur with increasing frequency with advanced age and loss of renal function. Some refer to this condition as adult polycystic liver disease (APLD), which occurs in 34 – 88 % of patients with APKD. Few patients with APLD do not have associated renal cysts. Hepatic cysts usually remain asymptomatic. Some of them develop complications including (1) cyst infection or hemorrhage; (2) biliary obstruction; and (3) portal hypertension. With improved management of the end-stage renal disease, hemodialysis, and renal transplantation, patients with APKD will have increased life expectancy. As a result, complications associated with hepatic cysts may become more common.
Literature
1.Mosetti MA, Leonardou P, Motohara T, Kanematsu M, Armao D, Semelka RC (2003) Autosomal dominant polycystic kidney disease: MR imaging evaluation using current techniques. J Magn Reson Imaging 18:210 – 215
2.Itai Y, Ebihara R, Eguchi N, et al. (1995) Hepatobiliary cysts in patients with autosomal dominant polycystic kidney disease: prevalence and CT findings. AJR Am J Roentgenol 164:339 – 342
3.Swenson K, Seu P, Kinkhabwala M, et al. (1998) Liver transplantation for adult polycystic liver disease. Hepatology 28:412 – 415
MR Imaging Versus Computed Tomography and Ultrasound
At MR imaging, multiple hepatic cysts can be characterized based on a unique combination of findings including low signal intensity on T1-weighted sequences, very bright signal on T2-weighted sequences with sharp margins, and absence of enhancement on all phases of dynamic gadolinium-enhanced including on delayed phase images. Cysts complicated with hemorrhage contain fluidfluid levels or diffuse high signal intensity on (fat-suppressed) T1-weighted sequences. Hemorrhage is particularly present in renal cysts (Figs. 6.1, 6.2). CT can also visualize liver and renal cysts but hemorrhagic cysts may be difficult to detect on CT examinations (Fig. 6.3). MR imaging is also preferred to CT in this patient group with renal dysfunction. Infected cysts will have imaging features of a pyogenic liver abscess with intraluminal debris and an enhancing wall (see also abscess p. 2).
Differential Diagnosis
Other conditions that present with multiple cystic lesions in the liver include biliary hamartomas (smaller cysts; incidental finding without APKD) and various types of Caroli’s disease (cysts located along the biliary tree and should communicate with adjacent bile ducts).
Management
Asymptomatic patients do not require any specific therapy. Optimal management of symptomatic patients with APKD is unclear. Percutaneous drainage is suitable for patients with single dominant cysts and is associated with universal recurrence of symptoms. Other treatment options such as cyst fenestration with or without resection provide unsatisfactory results as well. Orthotopic liver transplantation appears to be a more promising treatment option for patients with diffuse liver involvement with significant comorbid conditions.
6 Cyst IV – Adult Polycystic Liver Disease 13
Fig. 6.1. Cysts, drawings. T2 fatsat: cysts are much brighter with sharp demarcation to the liver. Note also renal cysts. T1 in-phase: cysts are hypointense to the liver. Some of the renal cysts have in part high signal due to hemor-
Fig. 6.2. Cysts, multiple, simple liver and complicated renal. A Axial fat-sup- pressed T2-w TSE image (T2 fatsat): Multiple simple liver and renal cysts are much brighter than the surrounding liver with sharp demarcation. The complicated renal cysts with hemorrhage have darker parts. B Axial inphase T1-w GRE (T1 in-phase): Hepatic cysts are hypointense to the liver. Note that parts of the complicated renal cysts are bright due to hemorrhage (fluid-fluid levels). C Axial arterial phase GRE image (ART): The cysts show no enhancement. D Axial delayed phase GRE image (DEL): The cysts remain
rhage (fluid-fluid levels). Note that these parts of the cysts are darker on T2 fatsat. ART: cysts show no enhancement; DEL: cysts remain unenhanced
unenhanced. E Coronal T2-w SSTSE image (T2 coronal): The hepatic and renal cysts are visible (arrows). F Axial opposed-phase GRE image (T1 op- posed-phase) contains less artifacts than the in-phase image. The renal cysts with hemorrhage are well visible (arrow). G Axial portal phase GRE image (POR): The cysts show no enhancement (arrows). H A detailed view from the axial delayed phase post-Gd 2D T1-w GRE image (POR): The cysts remain unenhanced with sharp demarcation to the surrounding liver (arrow)
Fig. 6.3. Cysts, CT, histopathology, and a drawing. A Unenhanced CT (another patient) shows multiple hepatic cysts. B CT in the portal phase shows no enhancement of the cysts. Note also cysts in the left kidney. C Photomicro-
graph shows multiple cysts with variable size. H&E, × 100. D Drawing shows multiple simple liver, and simple and hemorrhagic renal cysts