The authors report six cases of so-called spinal subdural arachnoid cysts, emphasizing the clinical and myelographic findings which, if not properly evaluated, may be misleading diagnostically. The literature of so-called perineural cysts and of extradural arachnoid cysts is likewise reviewed. Their clinical, roentgenological, and pathological features are examined. A common pathogenesis for all these lesions is proposed. It implies disruption and secondary proliferation of the arachnoid membrane. Hence, the term arachnoid diverticulum is advanced to include all lesions communicating with the subarachnoid space. Their varying relations with the subarachnoid space depend on the sites of the primary abnormalities and on hydrodynamic factors. Numerous observations of associated arachnoid diverticula, either perineural, subdural, or extradural, further favour a common pathogenesis.

YPERTROPHIC cervical pachymeningirls is a clinical syndrome characterized by compression of the spinal roots and spinal cord caused by a marked inflammatory hypertrophy of the cervical dura mater. The pathological process can spread to the leptomeninges and give rise, because of the progressive compression, to areas of softening of the spinal cord, where it is also possible to find cavities similar to those in syringomyelia. 26,29,4~ The cause of the disease is still unknown26,3~ The clinical picture is still that first described by Charcot in 18696 and Joffroy in 1873, TM who divided the evolution of the disease into three stages. The first stage is characterized by intermittent radicular pains in the neck, shoulders, and arms, which gradually become continuous. In the second stage, muscular weakness and atrophy develop in the arms. Finally, spastic paralysis of the legs, loss of various modalities of sensation, paresis of bowel and bladder, and respiratory disturbances characterize a third stage. The disease has been described in the cer-vico_thoraeic,S,2s,29.3t ,37 thoracic,~4 z~,25.3s.~9 and lumbar 1,11 regions, or along the entire extension of the spinal column, 6,24,27 with symptoms varying according to the level of the lesion. We are reporting five cases of hypertrophic spinal pachymeningitis operated upon during 1955 to 1965. We have excluded from this series 14 cases of chronic epidural inflammatory processes and 30 cases of spinal arachnoiditis operated on in the same period, even though some of these showed a moderate thickening of the spinal dura mater. Case Reports Case 1. S.S., a 3~-year-old male, entered the clinic on January 18, 1955, suffering from continuous pains in the buttocks, and numbness and weakness in both legs, of 3 weeks duration. He had no sphincteric dis

✓Prostaglandin (PGF2α) concentrations were measured by radioimmunoassay in serial samples of CSF from patients with subarachnoid hemorrhage, in an attempt to correlate these values with the presence or degree of the arterial spasm. Although elevated concentrations of PGF2α were found in most of these patients, when compared with a control series, there was no correlation between these values and the appearance of cerebral vasospasm. The results are discussed with reference to previous experimental work suggesting a role of PGF2α in the pathogenesis of cerebral vasospasm.

✓ Elevation of the tentorium and its dural sinuses, originally considered a diagnostic sign of Dandy-Walker cyst, may also occur in arachnoid cysts of the posterior fossa. Differentiation between these two lesions may be achieved angiographically by the evaluation of the posterior inferior cerebellar artery and its vermian branch, and of the inferior vermian vein. All these vessels are displaced forward and upward by an arachnoid cyst, while in the Dandy-Walker cyst the posterior inferior cerebellar artery is miniature and the vermian branch and the inferior vermian vein are absent.

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