Medusa head sign | Radiology Signs

Answer:

The Medusa head or caput medusae sign is the radial convergence of multiple dilated medullary veins onto a single enlarged transcortical or transependymal collector vein, seen on post-contrast T1-weighted images, on susceptibility-weighted imaging and in the venous phase of angiography. It is the defining appearance of a developmental venous anomaly, the commonest intracranial vascular malformation and an anatomical variant rather than a disease. The essential clinical point is that a developmental venous anomaly represents the normal venous drainage of that parenchyma, so it must never be resected or embolised; doing so causes venous infarction. It is almost always an incidental finding, and haemorrhage attributed to it is nearly always due to an associated cavernous malformation, which coexists in a substantial minority and is sought with susceptibility-weighted imaging. Other associations are a rare thrombosis of the collector vein, which produces oedema and can mimic tumour or infarct, and a co-existing sinus pericranii or, in the posterior fossa, a link with cerebellar cortical dysplasia. On CT the anomaly may be invisible or seen only as a linear enhancing structure, and on angiography the arterial phase is normal, which is what distinguishes it from an arteriovenous malformation with its early draining vein and nidus.

Why is it called so?

The dilated medullary veins radiating from the collector vein resemble the writhing snakes forming the hair of Medusa.

Pathophysiology

A developmental venous anomaly is thought to arise from an arrest or failure of normal medullary vein development in fetal life, so that a territory of otherwise normal brain drains through a single persistent enlarged channel instead of a mature network. The vessels are histologically normal veins separated by normal brain parenchyma, which is why the lesion neither bleeds nor grows. Because it carries the entire venous outflow of its territory, the collector vein is under higher flow than a normal vein and is therefore dilated and conspicuous. Chronic venous hypertension in the drained territory may explain the frequent association with cavernous malformations, which arise adjacent to the anomaly and are the actual source of any haemorrhage attributed to it.

Alternative names: Caput medusae sign; venous angioma

Other associated named signs: Popcorn appearance of an associated cavernous malformation and the palm tree sign used for the same drainage pattern

References

1. Nicolosi L, Tiralongo F, Inì C, Grippaldi D, Foti PV, David E, et al. Low-flow vascular malformations without arteriovenous shunting of the central nervous system: a pictorial review. Insights Imaging. 2026;17(1). PMID: 41774335.