[Extra-cerebral intracranial fluid collections in childhood: differentiation between benign subarachnoid space enlargement and subdural effusion using color-coded duplex ultrasound].

BACKGROUND

Extracerebral fluid collections in infancy are a common diagnostic problem, because by noninvasive imaging studies (including cranial ultrasonography, CT and NMR), no definite differentiation between two distinct pathological conditions can be found until today: An enlargement of the subarachnoid spaces in children with macrocephaly is a frequent observation of mostly unknown etiology but is known to be associated with a good prognosis. If surgery is necessary in these patients, ventricular shunting is required. On the other hand subdural effusions are often of traumatic origin and require frequently neurosurgical intervention (subdural shunting). Most reports on extracerebral fluid collections in infancy have not differentiated between both pathological conditions and therefore reveal confusing results. Recent studies using magnetic resonance imaging have shown that vascular flow phenomena in the arachnoid space can be used to a reliable diagnosis, whereas previous noninvasive neuroimaging attempts including high resolution computerized tomography (CT) have been useless.

PATIENTS AND METHODS

We investigated a cohort of 20 patients aged 4 mths to 30 mths (mean 10.5 +/- 6.6 months) 16 with the history of macrocephaly and normal neurological development and 4 patients after head trauma and symptoms of an elevated intracranial pressure.

RESULTS

In all 16 patients with the clinical diagnosis of benign subarachnoid space enlargement colour coded Doppler sonography detected archnoid vessels within the fluid collection, furthermore high resolution ultrasound demonstrated the dural border of of the arachnoidea as an echogenic membrane, an observation useful as a further sign of the subarachnoid location of the fluid collection. In the 4 patients with subdural hematoma the fluid collection showed an increased echogenity, no vascular structures and no surrounding border.

CONCLUSION

Out of these observations we conclude that high resolution ultrasound and colour-Doppler sonography are able to reliably differentiate between a subdural and a subarachnoid fluid collection. An NMR investigation with its higher risks (sedation, anesthesia) focused on this target only seems therefore to be not necessary in these patients.