Serpentine aneurysm is a rare subtype of intracranial aneurysm with a distinct appearance. It consists of a partially thrombosed giant intracranial aneurysm (≥ 25 mm) traversed by a patent serpiginous intra-aneurysmal vascular channel. This vascular channel has an entry and an exit point, differentiating it from a giant aneurysm (no exit point).
The clinical features are often related to local mass effect from the partially thrombosed giant aneurysm and will, as such, vary according to the affected territory . ~28% of patients will present with a ruptured aneurysm and subarachnoid hemorrhage .
Serpentine aneurysms involve the middle cerebral artery in ~50% of cases.
CT angiogram will demonstrate the patent intra-aneurysmal serpentine vascular channel and will also depict the often heterogeneous underlying partially thrombosed giant aneurysm.
The partially thrombosed giant cerebral aneurysm has a heterogeneous signal on MRI, reflecting the variable age of underlying blood products. The serpentine intra-aneurysmal vascular channel is best appreciated on angiographic sequences.
- T1: heterogeneous often with hyperintense foci in the partially thrombosed aneurysm
- T2: heterogeneous often with hypointense foci in the partially thrombosed aneurysm, flow voids within the serpentine intra-aneurysmal vascular channel; vasogenic edema may be seen in the adjacent parenchyma
- T2*: internal and peripheral susceptibility artefacts are usually seen
- MRA: enhancing serpentine intra-aneurysmal vascular channel
The inflow and outflow of the aneurysm are best appreciated on DSA.
The morphology of the patent intra-aneurysm tortuous vascular channel has been likened to a pretzel on DSA ('pretzel sign') .