preceding intracranial aneurysm clipping , a lumbar subarachnoid catheter can be placed to withdraw cerebrospinal fluid ( csf ) in order to facilitate surgical exposure . the dural defect created by the lumbar drain commonly seals spontaneously in a few days following catheter removal . persistent csf leakage in excess of its production can cause intracranial hypotension ( ih ) ranging in severity from a mild post - dural puncture headache ( pdph , i.e. , headache , neck stiffness , nausea , and dizziness ) to severe ih , " brain sag " , potentially causing midbrain herniation , pupillary dilation , hemorrhage , lethargy , coma , and death.13)19)21)24)26)28 ) symptoms usually are exacerbated with sitting and relieved when recumbent.26 ) previously , anesthesiologists have been cautioned against performing an epidural blood patch ( ebp ) in the presence of intracranial pathology.16 ) however , if the intracranial pathology is a direct result of persistent csf leak , an ebp may be life - saving.35 ) one of us ( p.p.h . ) observed that following open repair of anterior circulation aneurysms , some patients were more somnolent than would be anticipated based on surgery itself or other complications ( e.g. , residual ischemia or vasospasm ) . given our heightened awareness of possible ih following lumbar drain removal , we monitored clinically for brain sag and employed an ebp when indicated.2)6)20)27)34 ) we hypothesize that when there is evidence of persistent csf leakage contributing to brain sag , ebp may be a valuable supplement or alternative to trendelenburg therapy . a 25-year - old 160 cm tall woman weighing 73 kg had recanalization of a previously coiled anterior communicating artery aneurysm . a spetzler catheter was inserted at the l4 - 5 interspace and drained csf but the volume was not recorded . she complained of a positional headache , present while walking or sitting and absent when lying supine , ( fig . brain sag was diagnosed by progressive global neurological deterioration , orthostatic headache and computed tomography ( ct ) findings . on pod 6 , an l4 - 5 ebp was performed with 25 ml of autologous blood . within several hours , alertness improved , mental status returned to baseline , and headache fully resolved . she was discharged the next day . a 54-year - old 175 cm tall man weighing 84 kg underwent right craniotomy for clipping of an unruptured middle cerebral artery aneurysm . a spetzler catheter inserted at l4 - 5 interspace drained 100 ml of csf , and was removed post - craniotomy . the patient did well initially , however , on pod 3 , he developed a partial right third nerve palsy and lethargy . re - exploration was performed to address the mass effect attributed to the epidural collection . at craniotomy , however , the dura and brain were depressed and not under pressure . postoperatively , upright intracranial pressure ( icp ) was -14 mmhg , and increased to 0 with supine positioning . 2c ) , consistent with brain sag . two days after re - exploration , he was awake but confused , oriented to self , following only simple commands . he remained too lethargic to complain of positional headache but became more alert while supine . brain sag was confirmed by the constellation of persistent lethargy , third nerve palsy , radiographic findings and low icp ( 0 - 3 mmhg ) . seven days after aneurysm clipping , a l4 - 5 ebp was performed with 25 ml of blood . within the hour , he became more awake and appropriate . within four hours , he engaged in a telephone conversation and fully recovered to baseline neurological state . one day after ebp , he was ready for transfer to rehabilitation medicine and remained neurologically intact thereafter . a 47-year - old 160 cm tall woman weighing 59 kg presented with a ventricular drain was inserted to relieve hydrocephalus . following 2 days of medical optimization , the icp remained normal , she followed commands , and underwent craniotomy for aneurysm clipping . her postoperative head ct showed hemorrhagic contusions of the left frontal and temporal lobes likely due to surgical retraction . on pod 1 , ct showed diffuse cerebral edema , small lateral ventricles , effacement of the basal cisterns , and herniation of the left cerebellar tonsil through the foramen magnum ( fig . the neurological and radiological findings in conjunction with a soft skin flap and low icp led to the diagnosis of brain sag . twenty hours after drain removal , an l4 - 5 ebp was performed with 20 ml of blood . within 24 hours , the left pupil returned to baseline , both pupils were reactive , the left arm briskly localized while the right elicited weak extensor posturing , the icp increased to 12 mmhg , and the craniectomy site had normal tension . she gradually improved , and on pod 16 was transferred to rehabilitation facility . at 6 month follow - up , she had persistent right hemiparesis and breathed spontaneously on a tracheostomy collar . a 25-year - old 160 cm tall woman weighing 73 kg had recanalization of a previously coiled anterior communicating artery aneurysm . a spetzler catheter was inserted at the l4 - 5 interspace and drained csf but the volume was not recorded . she complained of a positional headache , present while walking or sitting and absent when lying supine , ( fig . brain sag was diagnosed by progressive global neurological deterioration , orthostatic headache and computed tomography ( ct ) findings . on pod 6 , an l4 - 5 ebp was performed with 25 ml of autologous blood . within several hours , alertness improved , mental status returned to baseline , and headache fully resolved . a 54-year - old 175 cm tall man weighing 84 kg underwent right craniotomy for clipping of an unruptured middle cerebral artery aneurysm . a spetzler catheter inserted at l4 - 5 interspace drained 100 ml of csf , and was removed post - craniotomy . the patient did well initially , however , on pod 3 , he developed a partial right third nerve palsy and lethargy . re - exploration was performed to address the mass effect attributed to the epidural collection . at craniotomy , however , the dura and brain were depressed and not under pressure . postoperatively , upright intracranial pressure ( icp ) was -14 mmhg , and increased to 0 with supine positioning . 2c ) , consistent with brain sag . two days after re - exploration , he was awake but confused , oriented to self , following only simple commands . he remained too lethargic to complain of positional headache but became more alert while supine . brain sag was confirmed by the constellation of persistent lethargy , third nerve palsy , radiographic findings and low icp ( 0 - 3 mmhg ) . seven days after aneurysm clipping , a l4 - 5 ebp was performed with 25 ml of blood . within the hour , he became more awake and appropriate . within four hours , he engaged in a telephone conversation and fully recovered to baseline neurological state . one day after ebp , he was ready for transfer to rehabilitation medicine and remained neurologically intact thereafter . a 47-year - old 160 cm tall woman weighing 59 kg presented with a ruptured left posterior communicating artery aneurysm , hunt - hess grade 4 . she was hemodynamically unstable with pulmonary edema and takotsubo 's cardiomyopathy . a ventricular drain was inserted to relieve hydrocephalus . following 2 days of medical optimization , the icp remained normal , she followed commands , and underwent craniotomy for aneurysm clipping . her postoperative head ct showed hemorrhagic contusions of the left frontal and temporal lobes likely due to surgical retraction . on pod 1 , her left pupil was dilated and minimally reactive to light . ct showed diffuse cerebral edema , small lateral ventricles , effacement of the basal cisterns , and herniation of the left cerebellar tonsil through the foramen magnum ( fig . the neurological and radiological findings in conjunction with a soft skin flap and low icp led to the diagnosis of brain sag . twenty hours after drain removal , an l4 - 5 ebp was performed with 20 ml of blood . within 24 hours , the left pupil returned to baseline , both pupils were reactive , the left arm briskly localized while the right elicited weak extensor posturing , the icp increased to 12 mmhg , and the craniectomy site had normal tension . she gradually improved , and on pod 16 was transferred to rehabilitation facility . at 6 month follow - up , she had persistent right hemiparesis and breathed spontaneously on a tracheostomy collar . nine previously reported patients developed brain sag following intracranial aneurysm clipping utilizing a lumbar drain , and were treated with ebp.2)5)6)27)34 ) in 8 of these patients , a rapid , significant , and permanent neurological improvement was reported . one patient with poor outcome after ebp had communicating hydrocephalus , which in conjunction with intraoperative lumbar drainage , caused brain sag and transtentorial herniation leading to intraoperative brainstem infarcts and duret 's hemorrhages.34 ) critical ih or " brain sag " was defined by komotar et al.22 ) as 1 ) clinical signs of transtentorial herniation ( e.g. , decline in mental status , pupillary asymmetry or non - reactivity , flexor or extensor posturing ) , 2 ) ct imaging revealing an oblong shaped brainstem with effacement of the basal cisterns , and 3 ) clinical improvement with 15 to 30 degrees of trendelenburg position . however , brain sag is more precisely defined as "  signs of transtentorial herniation unattributable to other known factors , in association with low intracranial pressure."3 ) in the 2006 report by the subarachnoid hemorrhage outcomes project,23 ) brain sag was identified in 16 of 167 patients ( 9.6% ) and was associated with global cerebral edema on initial head ct scan and a longer surgical duration . in the 2005 report by the same group,22 ) the 11 patients who developed brain sag were treated with trendelenburg position ( 15 to 30 degrees ) . clinical improvement was observed within 12 hours , while sustained symptom resolution required trendelenburg for an average duration of 2.8 days (  0.4 days , range 1 to 5 days).22 ) treatments for pdph are well - described.7)9)17)32)36 ) conservative management including supine bedrest and fluids provide symptomatic relief , but lack consistent long - term benefit.36 ) injection of autologous blood into the epidural space ( ebp ) usually provides rapid , effective , and durable symptom relief in the majority of cases.4)26)32)33)39 ) specific methods , indications , and contraindications for performing an ebp have been reviewed.7)14)15)26)29)30)32)36 ) two theories explain how an ebp relieves symptoms of pdph or ih : 1 ) injection of epidural blood compresses the lumbar cistern , increasing lumbar csf pressure , reducing traction on brain structures and 2 ) clotted blood causes mechanical tamponade , promoting dural sealing.8)11)141516)18)33)37)38 ) likely , both mechanisms are important ; immediate pain relief is a result of the compressive effect , and the prolonged benefit is due to dural sealing . mri demonstrates that 20 ml of blood injected into the epidural space disperses approximately 3.5 levels cephalad and 1 level caudad to the site of injection , mostly along the posterior dura , and acts to tamponade the thecal sac.9)37)40 ) early literature suggests ebp is successful in 90% of patients.1)14)16 ) in a randomized trial of 42 patients with pdph following diagnostic lumbar puncture , headache was absent or mild in 95% 24 hours after ebp ( 15 - 20 ml ) , whereas moderate or severe headache was observed in 90% of patients managed without an ebp.39 ) a prospective study of 504 patients with pdph ( after diagnostic lumbar puncture , n = 363 ; spinal or epidural anesthesia , n = 87 ; and other spinal injections , n = 54 ) , reported an ebp ( mean of 23  5 ml of blood ) provided complete or partial relief in 93% of patients.33 ) in a recent review of 29 patients with coma due to ih , an ebp was successful in reversing coma in 85% ( 6 patients required more than one ebp).26 ) if symptoms persist , the ebp can be repeated with improved outcome.1)4)36 ) in the setting of brain sag , despite limited study , it appears reasonable to inject at least 20 ml of autologous blood.12)31)33)39 ) crawford12 ) observed that ebp failed to correct pdph in 17% when the volume of injected blood was less than 20 ml , and that complete relief was observed in 91% of patients when the volume was increased to 20 - 25 ml . the timing of the ebp also may influence its efficacy ; performed within 24 hours after dural puncture , patching was unsuccessful in 71% , whereas after 24 hours it afforded full or partial relief in 96%.25 ) this is a retrospective series and brain sag may have been underdiagnosed . the 3 cases reported were clustered in the last 8 months of the 34 month reporting period , and some earlier patients may have been missed . there was no randomization or control group yet we clearly substantiated the clinical efficacy and expediency of an ebp in the setting of brain sag . it is reasonable to assess brain sag treatments in a larger prospective study . with regards to patient care , we now employ a more systematic approach to postoperative lumbar drain management to facilitate early diagnosis of ih and to differentiate ih from other causes of neurological decline . after the patient has fully recovered from general anesthesia and is neurologically stable , the lumbar drain is removed and the patient remains supine . while the patient is being monitored for signs of neurological decline , the head of the bed is elevated to 30. if there is possible brain sag , the patient is placed supine and observed for signs of clinical improvement . when ih is persistent or severe ( i.e. , brain sag evident on clinical examination and imaging studies ) , we more readily perform an ebp . to avoid exacerbating symptoms of ih ebp is a reasonable therapeutic option for persistent ih following clipping of an aneurysm , and it usually provides rapid and durable clinical improvement . an ebp should be performed only after thorough patient evaluation and in close collaboration with a neurosurgeon or neurologist . although performing an ebp in the presence of intracranial pathology may seem counterintuitive , the ebp may be lifesaving in that brain sag may lead to a far worse outcome .
intracranial hypotension ( ih ) can occur following lumbar drainage for clipping of an intracranial aneurysm . 
 we observed 3 cases of ih , which were all successfully treated by epidural blood patch ( ebp ) . 
 herein , the authors report our cases .