Abstract
The diagnostic advantages and disadvantages of conventional computerized tomography (CT), prolonged high dose delayed CT (PHDD-CT) and MRI are mainly discussed in 22 histologically verified cases of angiographically occult vascular malformations (AOVMs). The abnormal enhancement effect by conventional enhanced-CT (CE-CT) and PHDD-CT were demonstrated in 4 (22%) of 18 cases and in 11 (79%) of 14 cases. Contrast enhancement effect of PHDD-CT was more evident than that of CE-CT in all cases. In 4 cases, the lesions were more clearly delineated in PHDD-CT, In 7 cases, only PHDD-CT could demonstrate the lesions. The advantage of PHDD-CT was that it has a strong enhancement effect for AOVMs, On the other hand, in three cases with small hemorrhage and with enhancement effect, it was difficult to differentiate normal granulation from AOVM because PHDD-CT was performed early at one or two months after the onset. The disadvantages of PHDD-CT suggested that a long follow-up was needed until granulation completely disappeared in order to differentiate granulation from AOVM. In two of the three cases, which were difficult to define as AOVMs by PHDD-CT, MRI clearly demonstrated nidus as signal void and hemorrhage as high signal on T1-weighted and T2-weighted images. Signal void showing nidus of AOVMs was demonstrated in 2 (28%) of 7 cases by MRI. In the other two cases, MRI clearly demonstrated repeated hemorrhage which strongly suggested hemorrhage from AOVMs. The advantage of MRI is that it is capable of delineating nidus and various stage of hemorrhage. On the other hand, 4 cases of AOVMs were not defined as nidus in MRI. One disadvantage of MRI is that it is not able to demonstrate nidus with remarkably reduced flow. One other disadvantage of MRI is its inability to differentiate hyposignal or signal void secondary to calcification from these caused by flowing blood of nidus. A further disadvantage of MRI is that it is inappropriate for diagnosing residual AOVM after surgery because it strongly receives operative influence for a long time. Because it is not easy to demonstrate AOVM, in order to diagnose it, CT with PHDD-CT and MRI should be performed as much as possible taking into consideration the advantages, disadvantages and clinical course.
