Imaging of bridging vein thrombosis in infants with abusive head trauma: the "Tadpole Sign".

Objectives: Abusive head trauma (AHT) in infants is usually diagnosed using a multi-disciplinary approach by investigating the circumstances and identifying morphological indicators, for example, subdural hematomas (SDHs), subdural hygromas (SDHys), retinal haemorrhages and encephalopathy. The present morphological study investigates the incidence, radiological characteristics and non-radiological co-factors of bridging vein thrombosis (BVT) in infants with AHT.

Methods: From 2002 to 2013, computed tomography (CT) and magnetic resonance imaging (MRI) material of 628 infants aged 0-2 years were analysed retrospectively. If available, medicolegal expert opinions were additionally considered. Cases with SDHs and/or SDHys were identified and systematically evaluated as to the presence and characteristics of BVT.

Results: SDHs and/or SDHys were present in 29 of the 81 cases exhibiting morphological abnormalities in the initial CT. Among these, 11 cases (40%) had BVT (mean age = 5.0 months). BVT could be best depicted in the T1-weighted spin echo and T2*/susceptibility-weighted MRI. In one case, BVT could be depicted indirectly using time-of-flight MR venography. The predominant (73%) BVT shape was found to be tadpole-like ("Tadpole Sign").

Conclusions: In the absence of appropriate accidental trauma, BVT appears to be a strong indicator of AHT. Therefore, the BVT/Tadpole Sign represents compelling cause to search for other signs of AHT.

Key Points: • BVT is an excellent indicator of AHT in SDH/SDHy cases. • Accidental trauma must be ruled out before diagnosing AHT. • The Tadpole Sign appears to be the most characteristic shape of BVT. • BVT can be depicted using CT, MRI and MR venography. • The Tadpole Sign suggests searching for other signs of AHT.