Flash filling hepatic hemangiomas, also known as flash filling hepatic venous malformations, are a type of atypical hepatic hemangioma, which due to its imaging features often raises the concern of a malignant process rather than a benign one.
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Terminology
It is important to note that according to newer nomenclature (ISSVA classification of vascular anomalies) these lesions are known as venous malformations 5. Having said that it is probably helpful in reports to include the word 'hemangioma' as this term is ubiquitous in the literature and most familiar to many clinicians. The remainder of this article uses the terms 'flash filling hemangioma' and 'flash filling hepatic venous malformation' interchangeably.
Epidemiology
They may account for 16% of all hepatic hemangiomas 3.
Pathology
Being a subtype of hepatic hemangioma, it is also composed of dilated endothelial lined vascular channels and fibrous stroma.
Radiographic features
Most are small in size (<2 cm).
Ultrasound
On ultrasound, most are hyperechoic - same as the typical hemangiomas.
CEUS
During CEUS these lesions show rapid, homogeneous hyperenhancement followed by hyper/isoenhancement relative to the adjacent liver due to the retention of contrast until the late phase without washout 4.
CT
On CT, these lesions are normally iso- to hypodense on unenhanced scans. There is a quick, intense and homogeneous enhancement of the lesion in the arterial phase itself, hence the name "flash filling". In the rest of the phases, it retains the contrast and remains isodense to the adjacent vascular pool.
MRI
- T1: hypointense
- T2: markedly hyperintense
- C+ (Gd): prompt enhancement but no washout
Other general features
At times the venous matrix of these hemangiomas may develop phleboliths, which when recognized should be promptly associated with hemangioma.
Differential diagnosis
Due to the atypical feature of quick, brilliant arterial phase enhancement, these lesions have to be differentiated from:
- hepatocellular carcinoma
- hypervascular hepatic metastases (renal cell carcinoma, thyroid carcinoma, neuroendocrine tumor, choriocarcinoma, melanoma, breast carcinoma and leiomyosarcoma)
- focal nodular hyperplasia
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