How to Determine a Cryptic AN. Malformations. Clinico-Pathological Study of 16 Cases

The frequency of determination of cryptic AVM largely depends on the method of search during surgery. We introduced our method here together with a discussion of the microscopic and electron microscopic views. Generally, cryptic AVM is rarely found by angiography, and the key to its discovery is a skillful and thorough search for it during surgery rubbing all under a surgical microscope, the wall of the hematoma cavity is rubbed all over with a piece of cotton soaked with physiological saline solution, and a histological specimen is obtained from the easily-bleeding portion. We have performed patho-histological examinations on these specimens. In the last six years, we had 16 cases of histologically confirmed cryptic AVM, among them 12 cases were in the subcortex, and four in the brain stem. We suspected cryptic AVM in 15 cases having no histories of hypertension or blood diseases. Among these we found small nidi and achieved histological confirmations in 12. Of these 12, only seven had been found to have cryptic AVM by pre-operative angiography. They were found most frequently in the frontal lobe (8 cases), followed by the temporal lobe. In almost all, onset of cryptic AVM was relatively slow in spite of the presence of hematoma. Consciousness was clear and the outcome was generally good. Most of them were found in younger age groups, but we did find a few in older groups. In the four cases of cryptic AVM in the brain stem, there had been no particular indications of it before the operation. We are of the opinion that conventional histological classification of cryptic AVM is not adequate in view of the actual status.