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Neuroradiology

Haematoma, subdural

collection of blood in the subdural space, usually venous in origin and post-traumatic. The main sources of bleeding are thorn bridging veins. Rarely a subdural haematoma may be due to rupture of an aneurysm and subsequent laceration of the arachnoidal membrane. In this case the subdural haematoma is almost invariably associated with a subarachnoid haemorrhage.

Subdural haematomas are mainly frontoparietal in location and are usually crescentic in shape, compared to the lentiform shape of epidural haematomas (see haematoma epidural). The shape, however, also depends on the age and trophic state of the brain; in young patients a subdural haematoma may have a lentiform shape.

Subdural blood may extend along the falx, in the midline, thus producing interhemispheric subdural haematomas.

CT is the examination of choice; the extracerebral fluid collection is clearly seen as well as the associated signs of mass effect, consisting in flattening of the cerebral sulci, compression of the lateral ventricle, displacement of the midline structures and brain stem compression. The density varies according to age of the haematoma (Fig.1): an acute haematoma is hyperdense, becomes isodense in the subacute phase hypodense when chronic (i.e. more than 12 weeks old). Mixed densities may be seen in the hyperacute phase or in rebleedings within chronic haematomas. With bilateral subacute subdural haematomas the diagnosis may be difficult because of the absence of any asymmetrical mass effect. The ventricles may, however, appear smaller than they should for the patient's age and the sulci may be effaced.

MR shows, as well the distribution of blood, a mass effect and different signal intensities according to the age of the haematoma (Fig.2).

GS

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Fig.1

a. Axial CT without contrast. An inhomogeneous mixed hyperdense hypodense collection with a crescentic shape is seen over the frontoparietal convexity on the left side. The lateral ventricle is displaced and there is a marked shift of the midline structures. This is a hyperacute haematoma. b, c. Axial CT without (b) and with (c) contrast medium injection in a patient with bilateral isodense subacute subdural haematomas. The convexity sulci are effaced; without contrast the bilateral haematomas are poorly appreciated. After contrast initial enhancement of membranes (double arrows) helps the diagnosis. d. Axial CT without contrast of a chronic subdural haematoma over the left frontoparietal convexity. The haematoma has become hypodense, except for the most recumbent portion that is still slightly hyperdense.
Haematoma, subdural, Fig.1 (a)
Haematoma, subdural, Fig.1 (b)
Haematoma, subdural, Fig.1 (c)
Haematoma, subdural, Fig.1 (d)
Haematoma, subdural, Fig.2