Neuroradiology brain, MR, Education, Blood
S. Mahal, S. Tiwari, T. Yadav, P. K. Garg, P. S. Khera, B. Sureka
Findings and procedure details
The deep medullary veins are affected in a number of pathological conditions, either primarily or secondarily. A typical feature of these pathologies is that they show a characteristic distribution indicating the relationship to the medullary vein. Here, we will enumerate those causes (Fig 11).
- Structural anomalies of the medullary veins1
Developmental venous anomaly (DVA) (Fig 12-15)
- Most common intracranial vascular malformation (55% of all vacular malformations).
- Common locations: frontoparietal region(36-64%) and cerebellar hemisphere (14- 27%)
- Imaging: On imaging, they appear as medusa-like, mushroom-shaped, or umbrella-shaped lesions and are best visualised on SWI or post-contrast T1 weighted images. They consist of 3 segments.
- Types of DVA: Angiographically classified according to the drainage course of central (or stem) medullary veins, as either superficial or deep drainage types.
- Isolated DVAs do not require treatment or further evaluation.
- Vascular disorders
Medullary venous thrombosis3
- Cerebral venous thrombosis is a major cause of stroke, typically perinatal stroke.
- Thrombus may involve the major venous sinuses or the smaller medullary veins. Concomitant involvement of both is also seen. Medullary venous involvement can be of two types: a) deep medullary vein engorgement/ thrombosis, b) superficial medullary vein engorgement/ thrombosis.
- Both types can present with or without parenchymal changes like vasogenic/cytotoxic edema and intraparenchymal haemorrhage.
- Deep medullary venous thrombosis/engorgement: Both thrombosis and engorgement appear on SWI as prominent vessels. The ‘brush sign’4 and ‘iris sign’ are well-described signs in DMV involvement (fig16,17). Due to the centripetal drainage pattern of the DMVs, intraparenchymal haemorrhage is more common in deep medullary venous thrombosis .
- Superficial medullary venous thrombosis/engorgement: Due to the centrifugal pattern of drainage of SMVs, subpial haemorrhage is more common in superficial medullary venous thrombosis. Subpial haemorrhage is focal lobulated collection of blood between pial layer and displaced cortical surface of the brain. Temporal lobe is the most common location of this type of bleed. ‘Iris sign’ can also be seen.
- Traumatic disruption of medullary veins
Diffuse vascular injury1:
- High velocity trauma generates shear strain leading to the well- known diffuse axonal injury (DAI). Microhemorrhage within the white matter (typically in the parasagittal location) is another aspect of traumatic brain injury, termed as diffuse vascular injury (DVI).
- Microscopic findings of DVI is that of perivascular hemorrhages. They lack the edematous changes, that differentiate them from DAI.
- DVI lesions do not appear in the typical locations of DAI (Grey-white matter junction, corpus callosum, deep white matter, brainstem). They are rather seen converging towards the anterior horn of lateral ventricles, corresponding to the course of the DMVs. This is thus postulated that DVI occurs both due to shear strain and venous congestion of the DMV due to injury to the proximal veins.
- Inflammatory changes that spread along the vein:
- Most of the lesions show perivenular distribution as they are related to perivenular inflammation.
- Typical perivenular lesion includes ‘Dawson’s finger’ and ‘central vein sign’ shows that the inflammatory changes are mainly centred around medullary veins. (Fig 18)
- Miscellaneous causes causing engorgement of medullary veins:
Asymmetry of medullary veins in major cerebral arterial occlusion5,6 (Fig 19)
- Prominent deep and anastomotic medullary veins are seen in the periphery of ischemic infarcts resulting from occlusion of major arteries. This asymmetric dilatation of cortical and medullary veins on the ischemic side of the brain parenchyma is best appreciated on SWI.
- A number of studies have detected that appearance of asymmetric cortical and medullary veins is associated with more severe stroke and thus poor outcome. It is hypothesized that appearance of asymmetric medullary vein reflects the increase of deoxyhemoglobin in the draining DMV above a limit of detection. This is more likely to occur in severe strokes as it indicates the decompensation of oxygen capacity.
a) Prominent transcerebral veins in brain death7(Fig 20)
- Although the diagnosis of brain death is primarily based on neurologic criteria, imaging can provide corroborative evidence for the same.
- The ‘transcerebral vein’ sign and ‘cortical vein’ sign have been described in literature.
b) Role of deep medullary veins in pathogenesis of cerebral small vessel disease and lacunes8
- Few studies have shown that disruption of DMVs is the causative factor of small vessel disease and lacunes.
- Deep medullary venous collagenosis is the term used to encompass the venous pathologies that play a major role in small vessel disease in addition to the much celebrated arteriolar dysfunction.
c) Other pathologies involving the deep medullary vein include neurosarcoidois and intravascular lymphomas1