Cord sign | Radiology Signs

Answer:

The cord sign is a linear or serpentine hyperattenuating structure representing an acutely thrombosed cortical vein or dural sinus on unenhanced CT, seen as a dense cord running along the cortical surface or within a sinus. It is the unenhanced counterpart of the empty delta sign and, like it, is highly specific but insensitive; only a minority of proven cerebral venous thromboses show it. Attenuation of acute thrombus is typically 60 to 80 HU, and because normal flowing blood in a small vein can approach this, the finding is more reliable when the vein is expanded, when its density exceeds that of the adjacent arteries, or when the Hounsfield-to-haematocrit ratio is elevated. The confirmatory tests are CT venography, which shows the filling defect directly, and MRI with susceptibility-weighted or T2*-weighted sequences, on which thrombus blooms conspicuously, together with MR venography. Recognising a thrombosed cortical vein matters because isolated cortical vein thrombosis produces a juxtacortical haemorrhage or oedema that does not conform to an arterial territory and is easily mistaken for a contusion, tumour or atypical infarct. Pitfalls include polycythaemia, dehydration, subarachnoid blood layered in a sulcus adjacent to the vein, and a partially calcified falx.

Why is it called so?

The thrombosed vein appears as a dense linear structure resembling a cord laid on the brain surface.

Pathophysiology

When a cortical vein or sinus thromboses, the clot retracts and its haematocrit rises, concentrating haemoglobin and increasing X-ray attenuation, which is what makes it visible without contrast. The same clot is paramagnetic in its deoxyhaemoglobin phase, which is why it blooms on gradient-echo and susceptibility-weighted MRI, and its signal on conventional sequences changes over days as deoxyhaemoglobin converts to methaemoglobin. Occlusion raises pressure in the drained cortex, causing vasogenic and then cytotoxic oedema, and because venous pressure rises rather than falls the capillary bed remains perfused under high pressure and readily ruptures, which explains the high rate of haemorrhagic transformation compared with arterial infarction.

Alternative names: Dense vein sign; dense sinus sign

Other associated named signs: Empty delta sign after contrast and the dense triangle sign in the torcular region

References

1. Sadik JC, Jianu DC, Sadik R, Purcell Y, Novaes N, Saragoussi E, et al. Imaging of Cerebral Venous Thrombosis. Life (Basel). 2022;12(8). PMID: 36013394.