Neuroradiology

Germinal matrix haemorrhage

The germinal matrix is the site of origin of the vast majority of intracranial haemorrhages in preterm infants. The germinal matrix zone is a very unusual, highly vascularized and metabolically active structure that consists of proliferating neuroectodermal cells that appear during embryonic development along the lateral ventricular margin. The vessels supplying the germinal matrix are most evident between 24 and 32 weeks of gestation; beyond 32 weeks of gestation the neuroectodermal cells of the germinal matrix migrate toward the cerebral cortex with disappearance of the matrix zone.

The blood vessels within the germinal matrix are very fragile and consist of a single layer of endothelial cells, that is to say they are like capillaries. In addition there is a poor supporting stroma. These conditions therefore make them very vulnerable to damage and rupture when exposed to the stress suffered by almost all preterm neonates during the perinatal period.

If the haemorrhage is severe a transependymal rupture of the initial germinal matrix may occur, and the damage can extend into the surrounding cerebral parenchyma. Blood can also be found in the lateral ventricles, third and fourth ventricles and the basal cisterns of the brain. Intraventricular blood can lead to obstructive hydrocephalus. Parenchymal haemorrhage in the preterm neonate causes severe damage leading to destruction of brain substance, that will be replaced by porencephalic cyst.

Real-time ultrasound can easily detect germinal matrix-related haemorrhage, and is used for grading the severity of haemorrhage and in follow-up. The haemorrhage is seen as an increase in echogenicity and can be seen on the parasagittal view localized in the area of the caudothalamic notch or posterior caudate nucleus, or it may extend some distance anteriorly and involve the entire caudate nucleus. In the coronal view the hyperechogenic focus is usually located near the inferolateral border of the ventricular body, and may extend into the ventricular cavity.

CT scan shows the hyperdensity of extravasated blood laterally to the lateral wall of the frontal horn, involving the head of the caudate nucleus and within the lateral ventricles (Fig.1).

MR (Fig.2) is also highly informative but difficult to perform because of the poor clinical condition of these babies, particularly in the acute phase. In the chronic phase MR is helpful in determining the extent of brain damage and defining the precise topography of the lesions.

SG

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Fig.1

a, b. Axial and coronal CT in a preterm baby with large germinal matrix haemorrhage on the left and intraventricular haemorrhage.
Germinal matrix haemorrhage, Fig.1 (a)
Germinal matrix haemorrhage, Fig.1 (b)
Germinal matrix haemorrhage, Fig.2 (a)
Germinal matrix haemorrhage, Fig.2 (b)