Isotopic imaging, previously regarded as unrewarding in evaluation of posterior cranial fossa, through use of special projections and scanning techniques is currently reliable in diagnosis of certain neuro-otologic lesions. Pneumography via the lumbar route has long been regarded as primary diagnostic procedure for defining masses extending into posterior cranial fossa. Precise laminagraphy, preferably with circular or hypocycloidal motion, is essential for accurate diagnosis. Iophendylate (Pantopaque) cisternography is most useful for diagnosing intracanalicular acoustic neurinomas and small cerebellopontine angle masses. © 1973, American Medical Association. All rights reserved.