venerdì 6 giugno 2008
Figure 1 and Figure 2: Axial noncontrast CT images demonstrate multiple foci of increased attenuation within the brain.
Figure 3: Axial SPGR shows two lesions, the one in the midline is heterogenous in signal. The lesion in the posterior insula on the left is more homogeneously bright.
Figure 4 and Figure 5: Axial T2 and FLAIR images demonstrate the same lesion at the level of the third ventricle. Note there is no significant parenchymal edema. The lesion in the left brain does have associated hemosiderin deposition, but centrally the blood looks more acute to subacute.
Figure 6: Axial GRE image showing multiple lesions which demonstrate “blooming” secondary to hemosiderin deposition.
Diagnosis: Cavernous malformations
Cavernous malformations are sinusoidal collections of blood vessels surrounded by a single layer of endothelium without normal intervening brain parenchyma. They occur anywhere throughout the central nervous system but are most commonly seen in the cerebral hemispheres. CMs were traditionally believed to be congenital lesions, however, CMs also develop de novo following radiation therapy, or in association with developmental venous anomalies (see Case-in-point case on 2/9/07). Both congenital and sporadic forms present with seizures, hemorrhages, focal neurological signs, headaches, or patients can be entirely asymptomatic.
On unenhanced CT, CMs are hyperdense regions due to pooling of blood within the sinusoids and exhibit focal calcification. On MR, which is the preferred modality for evaluating CMs, there is a characteristic appearance demonstrating blood products of different ages appearing as a central region of high signal intensity (representing methemoglobin), surrounded by a rim of hemosiderin that is hypodense on T2W and gradient echo imaging. Angiographically, CMs are usually occult.
Approximately 25% of patients demonstrate multiple lesions and a small percentage of these patients follow a familial pattern. Many of these lesions may be too small and only identifiable on gradient echo MR. Gradient echo imaging has increased sensitivity for magnetic field inhomogenity because it does not contain a 180 degree refocusing pulse. As a result, if multiple lesions are detected on MRI, the familial form of CM should be suspected, and close relatives should undergo evaluation. Regardless of whether CMs are of congenital or acquired origin, they follow a common clinical course. The clinical course depends on the location of the lesion, the rate of expansion of the lesion and whether a clinically overt hemorrhage has occured.