EXTENSION OF POSTERIOR FOSSA TUMORS, PARTICULARLY INTRAVENTRICULAR FOURTH VENTRICLE TUMORS, INTO THE UPPER CERVICAL SPINAL CANAL

Intraventricular fourth ventricle tumors may be accompanied by emergence of tumor from the foramen of Magendie into the cervical spinal canal. This produces an appearance on air myelograms indistinguishable from tonsillar herniation, which also may be present. In 2 cases seen here, calcification present in tumor intruding into the cervical canal was visible on plain film roentgenograms. Because of the spreading of the tonsils anti upward displacement of the vermis incident to intraventricular fourth ventricle tumors, the posterior inferior cerebellar arteries may be shifted upwards, posteriorly anti laterally. If the tumor is supplied by these vessels, they may become dilated as well as displaced. If the tumor compresses the branches of the posterior inferior cerebellar artery, they become attenuated.

When a combination of a soft tissue mass in the cervical canal, failure of descent of the posterior inferior cerebellar arteries, and a midline tumor stain is noted, the possibility of an intraventricular fourth ventricle tumor bears consideration. This usually can be substantiated by means of pneumoventriculography.

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