Brain Tumors
Few data are available regarding the physiology of intracranial
tumors. Arbit and colleagues[590]
measured CBF
in
cerebral tumors with laser-Doppler technology. In general, they found that tumors
had lower CBF than normal brain did. Autoregulation was occasionally apparent, and
CO2
responsiveness was usually present. The investigation of Schregel
and coworkers, who measured MCA velocity and vessel area in tumor patients, also
revealed that CO2
responsiveness was occasionally abnormal and that ipsilateral
to the tumor, hyperventilation was sometimes associated with paradoxical increases
in MCA flow velocity.[591]
Animal experiments have
shown that regional CBF and CBV are higher in the tumor region and that the response
to hyperventilation (reduction in CBF and CBV) is preserved.[328]
Measurement of regional CBF in the area of the tumor might also be a useful predictor
of the grade of intracranial gliomas; both regional CBF and regional CBV are greater
with higher-grade gliomas.[592]
Considerable edema
is often found in association with intracranial tumors. Bedford and coworkers[593]
showed that the radiologic extent of the edema (which presumably represents the extent
of abnormal vessel leakiness) correlated with the severity of the elevation in ICP
that occurred in association with intubation-related hypertension. Empirically,
the edema associated with tumors is improved by steroids,[594]
and a reduction in tumor edema is accompanied by a reduction in regional CBF.[595]
In patients with intracranial tumors,[596]
BBB
function is improved by the administration of dexamethasone over a time course as
short as 6 hours. See Chapter 53
for a complete discussion.
