Hyun-Jung Jang

Purpose To describe fading hemangiomas [substantially lower attenuation (>30 HU) than vascular pool in the portal venous phase (PVP)] and to determine their incidence and characteristics on multiphasic CT. Methods The study population composed of 168 hemangiomas (≥5 mm) in 114 consecutive patients which were imaged on multiphasic CT and also proved by diagnostic findings on MRI. The size of hemangiomas and CT attenuation number of the enhancing area within the hemangioma, liver parenchyma, and portal vein were measured on both arterial phase (AP) and PVP images. The rapidity of enhancement (slow, P < 0.05) and rapid-fillers (P < 0.05). The proportion of fading hemangiomas was 52% (14/27) in flash-fillers, much more frequent than in rapid-fillers (4/27, 15%) as well as slow-fillers (9/27, 33.3%). The size of fading hemangiomas (17.9 ± 4.5 mm) was significantly smaller than that of non-fading (24.2 ± 3.6 mm) (P = 0.032). Although APS was more frequent in fading hemangiomas (55.6%, 15/27) than that of non-fading hemangiomas (37.6%, 53/141), there was no statistically significant difference (P = 0.086). Conclusions Sixteen percentage (27/168) of the hemangiomas in our study showed substantially lower attenuation than the portal vein in the PVP CT and this was more frequent in flash-fillers (52%, 14/27). The knowledge that fading does not preclude the diagnosis of hemangioma as well as of its high incidence in flash-fillers is important, as flash-filling hemangiomas with fading may cause a diagnostic challenge in patients suspected to have hypervascular malignancy.

Imaging plays a significant role in the diagnosis of vascular abnormalities of the liver and sometimes provides the only clue to the correct diagnosis. With advances of imaging techniques and multiphasic acquisition of liver imaging, various perfusion changes are frequently encountered. Correct imaging diagnosis of significant vascular diseases can prompt appropriate work-up and timely management. Accurate differentiation of clinically insignificant perfusion phenomena from clinically significant findings including neoplastic conditions and in the setting of post-transplantation is essential. This pictorial essay illustrates various perfusion and parenchymal changes associated with portal venous inflow, hepatic venous outflow, and non-portal venous third inflow and describes brief background pathophysiology and differential points.

Contrast-enhanced ultrasound (CEUS) has unique advantages over contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) in the characterization of hepatic tumors. These include the capability of real-time dynamic imaging depicting the enhancement pattern of tumors regardless of its rapidity, purely intravascular properties of the microbubble contrast agents more consistently demonstrating washout of malignancy, and capability of repetitive observation of tumor vascularity with multiple injections of microbubbles with an excellent safety profile and no nephrotoxicity. For an indeterminate mass detected on an ultrasound scan, an immediate benign diagnosis reduces the necessity of costly further imaging as well as patients’ anxiety and an immediate malignant diagnosis prompts the proper work-up and management. CEUS is often served as a problem-solving tool for indeterminate lesions on prior CT or MRI scans, obviating further invasive steps. CEUS offers excellent visualization of peripheral nodular enhancement in even flash-filling or very slow-filling hemangiomas. Careful observation of early arterial filling pattern is helpful in the differentiation of focal nodular hyperplasia versus adenoma. Hepatocellular carcinoma is typically characterized by arterial hypervascularity and often late, partial washout. Metastasis shows brief arterial hypervascularity and complete rapid washout, which can improve its detection during a portal phase survey. The washout phenomenon of malignant tumors in general is useful to differentiate them from benign lesions.

To retrospectively compare the arterial and portal venous phase enhancement patterns of hepatocellular carcinoma (HCC) at contrast material-enhanced ultrasonography (US) with the degree of HCC histologic differentiation. This study was approved by the research ethics board, and informed consent was obtained. The study population included 112 consecutive patients (91 men, 21 women; aged 25-86 years) with 112 histologically proved HCCs: 23 well differentiated, 77 moderately differentiated, and 12 poorly differentiated. All underwent continuous real-time low-mechanical-index contrast-enhanced US from wash-in of contrast material to 300 seconds by using a blood-pool microbubble agent. Initial image interpretation included arterial enhancement, dysmorphic intratumor arteries, and presence and time of negative enhancement (washout). Enhancement patterns were compared with histologic differentiation by using the Fisher exact test. In the arterial phase, 97 of 112 (87%) HCCs showed hypervascularity, with a significantly higher proportion in moderately differentiated HCCs (74 of 77, 96%) when compared with well- (14 of 23, 61%; P<.001) and poorly differentiated HCC (nine of 12, 75%; P<.004). Eight of 112 (7%) were isovascular and seven (6%) were hypovascular. Dysmorphic arteries were seen in 81 (72%) HCCs. Of 97 hypervascular tumors, only 42 (43%) showed typical washout by 90 seconds. Late washout appeared in 25 (26%) HCCs in the 91-180 seconds phase and in 21 (22%) in the 181-300 seconds phase. The remaining nine showed no washout up to 300 seconds and seven (78%) were well-differentiated HCCs. Moderately differentiated HCC generally shows classic enhancement features, while well- and poorly differentiated tumors account for most atypical variations. Extended observation in the portal phase is important as late washout occurs with slightly more frequency than washout in the conventionally defined portal venous phase.