Acute foramen magnum syndrome caused by an acquired Chiari malformation after lumbar drainage of cerebrospinal fluid: report of three cases

OBJECTIVE AND IMPORTANCE: The perioperative use of lumbar drainage of cerebrospinal fluid (CSF) is relatively common in neurosurgery, and the development of "acquired" Chiari malformations (tonsillar herniation) with lumbar CSF diversion procedures has been reported. CLINICAL PRESENTATION: We describe the history of three patients who developed a foramen magnum syndrome, attributable to acquired Chiari I malformations, after perioperative lumbar drainage of CSF. CONCLUSION: We propose that the mechanism responsible for Chiari I malformations involves a negative pressure gradient between the cranial and spinal regions, created by CSF drainage. Theories regarding the formation of acquired Chiari I malformations, the possible synergistic roles of intracranial pathological conditions and CSF drainage in the development of this entity, and the implications for the use of perioperative lumbar drainage are discussed.     

Death from chronic tonsillar herniation in a patient with lumboperitoneal shunt and Crouzon's disease.

A 2.5-year-old girl with Crouzon's disease, hydrocephalus, and a lumboperitoneal shunt died as a result of chronic tonsillar herniation (acquired Chiari 'malformation'). The possible synergistic role of the cranial dysmorphism and the lumboperitoneal shunt in the development of this anomaly is discussed. The literature is reviewed and it is argued that if hydrocephalus occurs in infants in whom cephalocranial disproportion is likely to develop, then it is inadvisable to insert a lumboperitoneal shunt.     

Chiari I malformation with underlying pseudotumor cerebri: Poor symptom relief following posterior decompression surgery

Introduction Pseudotumor cerebri (PTC) patients exhibit clear clinical signs and symptoms of higher intracranial pressure (ICP) without ventricular enlargement or mass lesions. The clinical picture of patients with PTC can sometimes be similar to that of Chiari Malformation type I (CMI). There is some evidence that Chiari I malformation and PTC may coexist, which raises the question of whether PTC is an idiopathic disease or a complication of posterior decompression surgery—treatment of choice for Chiari I malformation.Presentation of casesA retrospective review of electronic medical records of patients diagnosed with PTC at the University of Toledo Medical Center (UTMC) was performed. The objective was to determine whether PTC patients had a concurrent diagnosis of Chiari I malformation and whether the diagnosis of PTC occurred before or after posterior decompression surgery. Out of the 8 eligible patient medical records reviewed, 5 patients diagnosed with PTC had undergone posterior decompression surgery for Chiari I malformation at anywhere from several days to three years prior to being diagnosed with PTC. The diagnosis of PTC was based on temporary symptomatic relief following lumbar puncture which also showed elevated CSF opening pressures. Finally, a VP shunt was placed in each of the 5 patients to relieve the elevated intracranial pressure which resulted in the complete resolution of the patients' symptoms.DiscussionOur study focuses on patients who were diagnosed with and treated for CMI then reported back to the clinic within several days to three years complaining of symptoms of headache. Upon re-presenting to the clinic, a CSF flow study was performed which showed normal flow of CSF. Then, these patients underwent a lumbar puncture which demonstrated an elevated opening pressure (and ICP) and a temporary relief of the headache with lumbar drainage. A VP shunt was placed for each patient to treat for PTC, and the patients’ headaches were relieved.ConclusionThis study suggests that the presence of Chiari I malformation in a patient conceals the symptoms of PTC which may become apparent following posterior decompression surgery. Other possibilities could be that the patients are misdiagnosed for Chiari I malformation when they are in fact suffering from PTC, or that PTC is a complication of surgery.     

Long-term outcome of surgical management of adult Chiari I malformation

Chiari I malformation continues to inspire controversy. Debate still exists about surgical options. The aim of this study is to evaluate the long-term outcome of posterior fossa decompression procedure (PFD) in the treatment of adult Chiari I malformation, focusing on some factors or technical aspects which might influence the outcome. Forty-six adult patients with Chiari I malformation operated by PFD are the subject of this study. The group included 21 males and 25 females, with mean age of 37.4?years. Patients were divided into two groups: group I (32 cases) with syringomyelia and group II (14 cases) without syringomyelia. Group I was further subdivided into three subgroups according to the surgical procedure adopted: group Ia (12 cases) operated by PFD only, group Ib (14 cases) operated by PFD with fourth ventricular shunt, and group Ic (six cases) operated by PFD and syringosubarachnoid shunt. All cases included in group II were operated by PFD only. In group I, symptoms improved in 14 cases (43.8?%) and stabilized in 18 cases (56.3?%), whereas in group II, symptoms resolved in ten cases (71.4?%) and improved in four cases (28.6?%). Postoperative magnetic resonance imaging showed that the syrinx was resolved in 21 cases (65.6?%), improved in seven cases (21.9?%), and unchanged in four cases (12.5?%). Among the mean follow-up period (5.8?years), recurrence of symptoms occurred in five cases (10.9?%), all of them are included in group I, and were reoperated again. Posterior fossa decompression is recommended as the treatment of choice in adult Chiari I malformation with or without syringomyelia. The presence of syringomyelia predicts a less favorable response to surgical intervention. Syringosubarachnoid shunting did not improve the long-term outcome either clinically or radiologically. Implanting a fourth ventricular shunt in cases of syringomyelia associated with adhesions at the foramen of Magendie decreases the long-term incidence of recurrence significantly. For recurrent cases, re-exploration of the initial posterior fossa decompression is recommended before any consideration is given for direct management of the syrinx.     

Syringomyelia, its pathogenesis and surgical treatment based on 4 cases' experience

Four cases of syringomyelia, each were considered to have different pathogenesis of syrinx and presented different clinical and radiological pictures, are reported. Case I was associated with Chiari I malformation and the syrinx communicated with the fourth ventricle through the central canal, case 2 was associated with Chiari II malformation and the syrinx was not communicated with the fourth ventricle, case 3 was thought to be traumatic and case 4 to be arachnoiditis due to unknown etiology. Metrizamide CT myelography was most valuable diagnostic technique to disclose the syringomyelic cavity and its extension. The cases except case 1 showed central opacification without via fourth ventricle, suggesting transneural migration CSF as shown by Aubin et al. Surgical treatment, therefore, was different in each case to obtain normal CSF dynamics. Case 1 was treated by suboccipital craniectomy, muscle plugging to the obex and syringo-subarachnoid shunt. In case 2 syringo-cisternal shunt was done in addition to suboccipital craniectomy. In case 3 syringocisternal shunt was done after laminectomy. In case 4 syringo-peritoneal shunt was performed. All but case 4 were obtained favorable result and case 4 was unfavorable except the disappearance of girdle sensation. For traumatic or inflammatory syringomyelia with tight adhesion between pia and arachnoid membrane in subarachnoid space, syringocisternal shunt was good way to obtain normal CSF dynamics and was expected to relieve the neurological deterioration.     

Brainstem dysfunction in chiari malformation presenting as profound hypoglycemia: presentation of four cases, review of the literature, and conjecture as to mechanism.

OBJECTIVE: We report four patients whose cases resulted in our observation that profound hypoglycemia resulting from intermittent hyperinsulinism plays a significant role in patients with brainstem dysfunction from Chiari I or II malformations who have intermittent autonomic dysfunction ("blue spells"). METHODS: The records of four children with severe brainstem dysfunction associated with hindbrain herniation (Chiari I or II malformation) were reviewed retrospectively. Each patient had severe lower cranial nerve dysfunction that required tracheotomy and feeding tube placement. After we found that profound hypoglycemia had occurred during a spell of autonomic dysfunction in one patient, the charts of the other three patients were reviewed for evidence of hypoglycemia. Now, whenever one of them has evidence of autonomic dysfunction, prospective studies of glucose and insulin levels are performed. Three of the patients had Chiari II malformation in association with myelomeningocele, and one patient had a Chiari I malformation resulting from Pfeiffer's syndrome. RESULTS: Hypoglycemia occurred in these patients episodically, and usually when their shunts were functioning. The hypoglycemia was associated with hyperinsulinemia in each patient. The brainstem structures of these children (presumably the dorsal motor nuclei of the vagus) were extremely sensitive to changes in local or regional intracranial pressure. These changes were triggered by intermittent shunt failure, agitation from pain, abdominal distention from constipation, and retention of CO2. In patients with Chiari malformations, even mild increases in intracranial pressure lead to brainstem dysfunction. One possible explanation is that pressure on the deformed Xth cranial nerve nuclei may lead to insulin release and life-threatening hypoglycemia. Continuous-drip feeds are necessary to prevent this complication. CONCLUSION: Patients with severe intermittent brainstem dysfunction after decompression of Chiari I or Chiari II malformations should have laboratory studies of glucose levels performed at the time of the episodes to rule out hypoglycemia.     

Syringomyelia with Chiari malformation; 3 unusual cases with implications for pathogenesis

Summary Syringomyelia is an important cause of neurological deficit. Most cases of non-traumatic syringomyelia occur in association with a Chiari malformation. We present three unusual examples of syringomyelia with such an association. The first case is that of syringomyelia in a young woman with Marfans syndrome, a spontaneous CSF leak and intractable intracranial hypotension. The second is a woman with long-standing lumbo-peritoneal shunt for pseudotumour cerebri who developed an acquired Chiari malformation. A young woman with a Dandy-Walker cyst that herniated into the upper cervical canal is the third case. These cases provide a basis for discussion of the pathogenesis and management of syringomyelia and the Chiari malformation in such cases.     

Chiari type 1 malformation and magnetic resonance imaging

The Chiari type 1 malformation is common. Unlike the Chiari type 2 and 3 malformations, it may remain latent for a long time, becoming symptomatic only in adulthood. The introduction of MRI has resulted in an increased number of diagnoses of this malformation in pediatric patients. It appears to be related to underdevelopment of the posterior cranial fossa. It must be differentiated from acquired tonsillar herniation, particularly when herniation results from intracranial hypotension; these cases are sometimes reported as acquired Chiari I malformation with spontaneous resolution. Tonsillar ectopia may cause symptoms by its direct effect on any or all of the medulla and the cerebellar and upper spinal cord. The most suggestive of the oculomotor disturbances is oscillopsia with downbeat nystagmus. Dysphonia and dysphagia are common. Potentially serious autonomic disturbances are also frequent: sleep apnea, respiratory failure, syncope and even sudden death. Another risk is syrinx formation, resulting from obstruction of CSF circulation in the cisterna magna. Syringomyelia is detected in 32 to 74% of patients with Chiari I malformation. Treatment is surgical. Posterior fossa decompression is achieved by suboccipital craniectomy combined with laminectomy of the upper cervical segments. Surgical intervention is indicated when the malformation is symptomatic and there is no doubt that it is the cause of the symptoms. When a Chiari I malformation is identified fortuitously on MRI, long-term monitoring is essential. The risk of developing symptoms increases over time. Patients should be advised not to participate in contact sports.     

Decompression of the spinal subarachnoid space as a solution for syringomyelia without Chiari malformation

STUDY DESIGN: Review and analysis of seven cases of syringomyelia treated surgically. OBJECTIVE: To demonstrate the beneficial role of decompressive surgery for the altered cerebrospinal fluid (CSF) flow dynamics in syringomyelia not associated with Chiari I malformation. A comparison between the pre- and post-operative syrinx size and CSF flow in the subarachnoid space was made using cine-mode magnetic resonance imaging (cine-MRI) and then correlated with clinical improvement. SETTING: University Hospital, Seoul, Korea. METHODS: Conventional spinal MRI and cine-MRI were performed in the region of CSF flow obstruction preoperatively in seven patients with syringomyelia not associated with Chiari I malformation. The group consisted of one case of syrinx with post-traumatic compression fracture, one case of post-traumatic arachnoiditis, two cases of holocord syrinx associated with hydrocephalus without Chiari malformation, one case of syrinx with post-traumatic pseudomeningeal cyst, one case of post-laminectomy kyphosis-associated syringomyelia and one case of post-tuberculous arachnoiditis syringomyelia. Based on the preoperative cine-MRI, the types of surgery appropriate to correct the CSF flow obstruction were chosen: decompressive laminectomy-adhesiolysis and augmentation duraplasty in arachnoiditis cases, ventriculoperitoneal shunt for hydrocephalus, cyst extirpation in pseudomeningeal cyst and both anterior and posterior decompression-fusion in the case of post-laminectomy kyphosis. A syrinx-draining shunt operation was performed in three cases; where the syringomyelia was associated with post-traumatic compression fracture refractory to a previous decompression, where hydrocephalus was present in which the decompression by ventriculoperitoneal shunt was insufficient and where post-traumatic arachnoiditis was present in which the decompression was impossible due to diffuse adhesion. Change in syrinx size was evaluated with post-operative MRI in all seven cases and restoration of flow dynamics was evaluated with cine-MRI in three of the cases, two patients with clinical improvement and one patient with no change of clinical status, respectively. RESULTS: Four out of seven patients showed symptomatic improvement after each decompressive operation. In the remaining three cases, reconstruction of the spinal subarachnoid space was not possible due to diffuse adhesion or was not the main problem as in the patient with syrinx associated with hydrocephalus who had to undergo a shunt operation. One of these three patients showed clinical improvement after undergoing syringosubarachnoid shunt. A decrease of syrinx size was observed in only two out of the five patients who showed clinical improvement after treatment. Of these five patients, two patients underwent post-operative cine-MRI and the restoration of normal CSF flow dynamics was noted in both patients. Of the remaining two patients, one underwent post-operative cine-MRI and there was no change in the CSF flow dynamics evident. CONCLUSION: These results suggest that the restoration of CSF flow dynamics between the syrinx and the subarachnoid space by decompressive operation is more effective than simple drainage of the syrinx cavity itself in the treatment of syringomyelia without Chiari malformation.     

脾静脉与颈内静脉转流术治疗重症布-加综合征

目的探索重症布－加综合征的手术方式。方法自１９９４年１１月至１９９６年５月,对１７例重症布－加综合征患者采用脾切除、脾静脉－颈内静脉转流术进行治疗。结果随访３～２０个月,效果优者１１例（６４．７％）,良好者５例（２９．４％）,死亡１例（５．８％）。结论对重症布－加综合征患者,脾静脉－颈内静脉转流是一种有效的手术方式。     

Management of cerebellar ptosis following craniovertebral decompression for Chiari I malformation

OBJECT: In this report the authors review their experience in the treatment of seven patients with symptomatic cerebellar ptosis following craniovertebral decompression (CVD) for Chiari I malformation. METHODS: The mean age of the patients was 37 years and the average amount of time between the initial suboccipital craniectomy and evaluation for cerebellar ptosis was 6.8 years. Five patients presented primarily with intractable headache and the remaining two patients with neurological deficits caused by recurrent syringomyelia. Three different surgical modalities were used to treat these patients: ventriculoperitoneal shunt placement (one patient), syringoperitoneal shunt placement (two patients), and partial suboccipital cranioplasty with or without intradural exploration (four patients). The mean follow-up period was 51 months. The three patients who underwent shunt placement procedures experienced poor results, with no evidence of symptom relief and continued neurological deterioration. In contrast, all four patients who underwent cranioplasty experienced good or excellent clinical outcomes. Postoperative magnetic resonance imaging studies revealed a reduction in the size of the syrinx cavity in patients who simultaneously underwent intradural exploration. CONCLUSIONS: The emergence of symptomatic cerebellar ptosis following CVD for Chiari I malformation is primarily caused when the suboccipital craniectomy is too large for the specific patient. The cerebellar ptosis usually presents with severe headache and/or neurological deficit due to persistent or recurrent syringomyelia. Partial suboccipital cranioplasty, with or without intradural exploration, is effective in treating this condition.     

Syringo-subarachnoid shunt for syringomyelia associated with Chiari malformation (type 1)

Summary The authors report the surgical results of 28 patients with syringomyelia associated with Chiari malformation (type 1). 28 patients underwent 34 operative procedures. Syringo-subarachnoid shunt was performed in 28 patients, foramen magnum decompression with syringo-subarachnoid shunt in three, ventriculo-peritoneal shunt in one, terminal syringostomy in one, and foramen magnum decompression with terminal syringostomy in one. In an average postoperative follow-up period of 3 years and 9 months ranging from one year to 7 years and one month, neurological symptoms and signs improved in 24 out of 28 patients (82%). Some improvement was noted in sensory deficit and motor weakness. In 3 patients, the symptoms did not change. In 3 patients whose symptoms were unchanged, preoperative studies demonstrated atrophy of the spinal cord, in which irreversible changes were shown. The symptoms deteriorated in one patient. In one patient whose symptoms increased 3 months after syringo-subarachnoid shunt, shunt insufficiency due to postoperative adhesive arachnoiditis was responsible for neurological deterioration.The authors propose that syringo-subarachnoid shunt is effective as a surgical procedure for syringomyelia associated with Chiari malformation (type 1) if the patient does not have symptoms due to Chiari malformation or has only mild signs and symptoms which do not require foramen magnum decompression, such as nystagmus or atrophy of sternocleidomastoid muscle.     

Syringobulbia Caused by Delayed Postoperative Tethering of the Cervical Spinal Cord – Delayed Complication of Foramen Magnum Decompression for Chiari Malformation

Summary  Postoperative tethering of the high cervical spinal cord is a rare cause of neurological deterioration after foramen magnum decompression (FMD) with duraplasty for Chiari type I malformation. A review of the literature revealed that only 5 cases have been reported. This entity is not widely known to occur as a complication of the common surgical procedure for Chiari type I malformation. A 17-year-old boy experienced rapidly progressive neurological deterioration over a 3-month period. FMD and duraplasty with lyophilized cadaver dura had been performed 8 years previously. Follow-up MR images showed that the cerebrospinal fluid (CSF) space dorsal to the cord was gradually disappearing and that syringobulbia had developed. Opening the dura mater of the posterior fossa revealed dense fibrous scarring, arachnoid thickening over the cervicomedullary area, and tethering the cord to the dura from the medulla to C2. The adhesions were dissected free, and the tethering was released. A syringosubarachnoid (SS) shunt was inserted and duraplasty was performed with an expended polytetrafluoroethylene sheet (Gore-Tex). Postoperative MR images demonstrated that the syringobulbia had completely collapsed and that a dorsal CSF space was present. Follow-up MR images provided significant information on the cervical spinal cord tethering after FMD with duraplasty for Chiari malformation. We encourage sharp surgical detethering and duraplasty with Gore-Tex to avoid retethering. Early recognition and treatment of this unusual but important complication are emphasized.     

Hidden aqueductal stenosis associated to bilateral idiopathic foramina of Monro stenosis mimicking a Chiari I malformation? Case report

A 39-year old man came to our outpatient clinic with long history of unspecific symptoms and signs. Cerebral MRI showed herniation of the cerebellar tonsils of more than 1?cm below the foramen magnum and a triventricular hydrocephalus. A diagnosis of Chiari I malformation was retained. After an osteo-dural decompression of the posterior fossa, post-operative MRI revealed an aqueductal stenosis with triventricular hydrocephalus. An endoscopic-third- ventriculostomy showed an idiopathic stenosis of the right foramen of Monro. Residual symptoms and persistence of biventricular hydrocephalus justified a ventriculo-peritoneal shunt. Aqueductal and foramina of Monro stenosis can mimick a Chiari I malformation.     

内皮细胞衬里人工血管静脉旁路移植10例

为进一步证实内皮细胞衬里人工血管的临床效果,报告临床应用１０例的长期随访。方法,本组１０例布加综合征病人,行腔房转流术６例,肠房转流术２例,肠颈转流术和肠腔转 流术各１例。应用人工血管内径１４ｍｍ,长８－３０ｃｍ,其中针织涤纶２根,编织涤纶７根,带外支持环ＰＴＦＥ１根。     

Chiari畸形的研究进展

Chiari畸形是以小脑扁桃体下疝畸形为特，止的先天性疾患，目前较为公认的理论是起源于胚胎中胚叶轴旁的枕骨原节发育不良所敏，其诊断主要依赖于MRI。根据解剖上的异常，通常分为4型。临床分型有利于术式的选择，有Pillay、Bindal等分型，但尚无公认的分型。手术是治疗Chiari畸形的唯一有效方法，针对不同病情相位采取后颅窝减压、分流术或减压加分流手术，大部分患者的症状和体征可以得到改善。     

布加综合征452例术后并发症的处理

目的　探讨布加综合征术后并发症的预防和治疗经验。 方法　从１９９１ 年７ 月至１９９８年３ 月,我院共收治４５２ 例患者,男２６０ 例,女１９２ 例,年龄２～７２ 岁,平均３２－７ 岁。根据病理分型和临床分期,共施行各种手术３９７ 次。主要的术式包括肠房转流术（７８ 例）,腔房转流术（６５ 例）,肠腔分流术（４１ 例） ,肠颈转流术（３６ 例） ,根治术（３１ 例） ,联合破膜术或加支架置入（２１ 例）,球囊扩张加支架置入术（１０５ 例）,肠腔分流加支架置入（１０ 例） ,脾房分流术（２ 例） 。 结果　术后主要并发症１２９ 例,发生率为３２－５％ 。２２ 例在术后１ 个月内因肝肾综合征等严重并发症而死亡,病死率为５－５％ 。有１８ 例因并发症再次手术,其余患者经各种治疗后恢复良好。 结论　布加综合征术后可发生较多并发症,但只要仔细观察,认真处理,可以得到有效治疗     

Hydrosyringomyelia and its management in childhood

Syringomyelia, once regarded as a degenerative disease of adults, is now recognized to be a disorder usually associated with the Chiari malformation and occurring in patients of all ages. We have reviewed 47 patients with syringomyelia treated on the Neurosurgical Service at the Hospital for Sick Children during the years 1977 to 1985. Twelve of these patients had a Chiari I malformation, 30 had a Chiari II malformation, and 5 had an acquired Chiari malformation. Thirty-one of these patients were treated by decompression of the Chiari malformation and plugging of the obex, 5 were treated by a simple posterior fossa decompression, 9 were treated by shunting of the syringomyelic cavity, and 2 were treated by a combined decompression of the posterior fossa and shunting of the syrinx. The Gardner procedure (decompression of the Chiari malformation and plugging of the obex) was the procedure most commonly used in managing our group of patients and resulted in improvement in over 70% of patients.     

Resolution of syringomyelia and Chiari I malformation by ventriculoatrial shunting in a patient with pseudotumor cerebri and a lumboperitoneal shunt

A sneeze caused acute left arm pain in a 36-year-old woman with a lumboperitoneal (LP) shunt that had been placed 3 years earlier for relief of headaches caused by pseudotumor cerebri. Numbness progressed up the left arm, neck, and back of the head and finally into the left face along with weakness of the hand and arm. Magnetic resonance imaging (MRI) and computed tomography revealed new tonsillar herniation and a large eccentric syrinx extending from C2 to T6. The functioning LP shunt was clamped, and a ventriculoatrial shunt was placed. Pain lessened and motor function improved slightly. MRI revealed complete resolution of the syrinx and resolution of the tonsillar herniation. Theories of syringomyelia formation, the relationship to Chiari I malformation, and the implications of this case are discussed.     

Surgical management of Chiari I malformation based on different cerebrospinal fluid flow patterns at the cranial-vertebral junction

Chiari I malformation has been shown to present different cerebrospinal fluid (CSF) flow patterns at the cranial-vertebral junction (CVJ). Posterior fossa decompression is the first-line treatment for symptomatic Chiari I malformation. However, there is still controversy on the indication and selection of decompression procedures. This research aims to investigate the clinical indications, outcomes, and complications of the decompression procedures as alternative treatments for Chiari I malformation, based on the different CSF flow patterns at the cranial-vertebral junction. In this study, 126 Chiari I malformation patients treated with the two decompression procedures were analyzed. According to the preoperative findings obtained by using cine phase-contrast MRI (cine PC-MRI), the abnormal CSF flow dynamics at the CVJ in Chiari I malformation was classified into three patterns. After a preoperative evaluation and an intraoperative ultrasound after craniectomy, the two procedures were alternatively selected to treat the Chiari I malformation. The indication and selection of the two surgical procedures, as well as their outcomes and complications, are reported in detail in this work. Forty-eight patients underwent subdural decompression (SDD), and 78 received subarachnoid manipulation (SAM). Ninety patients were diagnosed as having Chiari I malformation with a syrinx. Two weeks after the operation, the modified Japanese Orthopedic Association (mJOA) scores increased from the preoperative value of 10.67 ± 1.61 to 12.74 ± 2.01 (P < 0.01). The mean duration of follow-up was 24.8 months; the mJOA scores increased from the postoperative value of 12.74 ± 2.01 to 12.79 ± 1.91 at the end of follow-up (P = 0.48). More complications occurred in the patients who underwent SAM than in those who received SDD (SAM 11 of 78 (9.5%) vs SDD 2 of 48 (3.5%)). The abnormal CSF flow dynamics at the CVJ in Chiari I malformation can be classified into three patterns. A SAM procedure is more feasible in Chiari I malformation (CM1) patients with pattern III CSF flow dynamics, whereas a SDD procedure is more suitable for CM1 patients with pattern I CSF flow dynamics. In CM1 patients with pattern II CSF flow dynamics, an intraoperative ultrasound after craniectomy could play an important role in the selection of an effective decompression procedure.