J Neurosurg / Volume 115 / November 2011 J Neurosurg 115:1031–1037, 2011 1031 N egative-pressure and low-pressure hydrocepha- lus cases are clinical entities distinct from other types of hydrocephalus. Both entities are deined by the presence of very low or negative iCp and ventricu- lomegaly. the presentation is quite rare and has been de- scribed in patients with subarachnoid hemorrhage, 5,21,29,32 intraventricular hemorrhage, 21 lumbar puncture, 9 menin- gitis, 21 posterior fossa tumors, congenital aqueductal ste- nosis, spinal arachnoid cysts, 39 hemispherectomy, 7 and normal-pressure hydrocephalus. 4,5,28,29,35 patients with low- or negative-pressure hydrocephalus frequently un- dergo multiple shunt revisions, without success in revers- ing the signs of ventriculomegaly. the neurological clini- cal course is insidious. patients show a declining level of consciousness and function, with decreases in areas such as appetite, energy, speech, motor function, and balance. Although low pressure is the cornerstone of the deini- tion, the clinical picture is similar to ventriculomegaly as- sociated with high iCp symptoms in that they share signs and symptoms such as low level of consciousness, head- aches, vomiting, and cranial neuropathies. 29,35,39 Negative-pressure and low-pressure hydrocephalus: the role of cerebrospinal luid leaks resulting from surgical approaches to the cranial base report of 3 cases Aristotelis s. Filippidis, M.d., ph.d., M. Y AshAr s. KAlANi, M.d., ph.d., peter NAKAJi, M.d., ANd hArold l. reKAte, M.d. Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona Object. Negative-pressure and low-pressure hydrocephalus are rare clinical entities that are frequently misdiag- nosed. they are characterized by recurrent episodes of shunt failure because the intracranial pressure is lower than the opening pressure of the valve. In this report the authors discuss iatrogenic CSF leaks as a cause of low- or negative- pressure hydrocephalus after approaches to the cranial base. Methods. the authors retrospectively reviewed cases of low-pressure or negative-pressure hydrocephalus pre- senting after cranial approaches complicated with a CSF leak at their institution. Results. Three patients were identiied. Symptoms of high intracranial pressure and ventriculomegaly were pres- ent, although the measured pressures were low or negative. A blocked communication between the ventricles and the subarachnoid space was documented in 2 of the cases and presumed in the third. shunt revisions failed repeatedly. in all cases, temporary clinical and radiographic improvement resulted from external ventricular drainage at subatmos- pheric pressures. The CSF leaks were sealed and CSF communication was reestablished operatively. In 1 case, neck wrapping was used with temporary success. Conclusions. Negative-pressure or low-pressure hydrocephalus associated with CSF leaks, especially after cranial base approaches, is dificult to treat. The solution often requires the utilization of subatmospheric external ventricular drains to establish a lower ventricular drainage pressure than the drainage pressure created in the sub- arachnoid space, where the pressure is artiicially lowered by the CSF leak. Treatment involves correction of the CSF leak, neck wrapping to increase brain turgor and allow the pressure in the ventricles to rise to the level of the opening pressure of the valve, and reestablishing the CsF route. (DOI: 10.3171/2011.6.JNS101504) KeY Words • cerebrospinal luid • hydrocephalus • negative pressure • leak • low pressure • neck wrapping 1031 Abbreviations used in this paper: Csas = cortical subarachnoid space; eCF = extracellular fluid; etv = endoscopic third ventricu- lostomy; evD = external ventricular drain; iCp = intracranial pres- sure; vp = ventriculoperitoneal. see the corresponding editorial in this issue, pp 1029–1030.