Brainstem Conundrum: The Chiari I Malformation

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VOLUME 13, ISSUE 4, APRIL 2001 154

CLINICAL PRACTICE

Brainstem Conundrum: The Chiari I Malformation

Diane Mueller, ND, RN, C-FNP

Case StudyMs. S was a 35-year old woman with approximately seven years of progres-

sive neurologic deterioration. Her primary presenting symptoms included poste-rior-occipital headaches, described as intense pressure and often associated withnausea; shortness of breath, unrelated to exertion; and dizziness. She reportedprogressive numbness in the hands and had unknowingly burned herself on sev-eral occasions. Weakness of the extremities had progressed to inability to holdobjects and gait instability. The neurologic examination was remarkable for sig-nificant weakness of the upper and lower extremities, numbness throughout theleft, and gait ataxia. She had been treated conservatively by her primary careprovider for approximately eight years for stress and underwent an admission topsychiatry for a presumed diagnosis of conversion reaction. A magnetic reso-nance imaging (MRI) scan was performed and demonstrated approximately10mm tonsillar herniation consistent with Chiari I Malformation, andsyringomyelia extending from cervical three to thoracic nine level.

INTRODUCTION

Chiari I Malformation (formerly referred to as Arnold-ChiariMalformation) is an unusual congenital neuroskeletal deformity. The exactpathogenesis and incidence of the disorder is unknown. Theories suggestthat the malformation occurs during embryologic development of the cer-vico-medullary junction. An abnormally small posterior fossa forces thetentorium inferiorly, resulting in caudal displacement of the cerebellum(Paul, Lye, Strang, & Dutton, 1983). (Figures 1 & 2)

The Chiari I Malformation was first described by Cleland in 1883 as apathologic finding in nine infants at post-mortem examination (Carmel,& Markesbery, 1972). Following this publication, in 1891, Chiaridescribed the anomaly as a hindbrain deformity and delineated two dis-tinct types: the Type 1 anomaly, which was described as elongation of thecerebellar tonsils, and Type 2, which depicted lengthening of the cerebel-lum as well as abnormality of the fourth ventricle. This traditional nomen-clature has remained; however, the current classification has evolved toinclude four distinct types of Chiari Malformations.

Chiari 1 Malformation (often called the adult Chiari Malformation)is described as caudal displacement of the cerebellar tonsils below the levelof the foramen magnum. Chiari I Malformation has classically beendefined as tonsillar herniation of three to five millimeters below the levelof the foramen magnum (Milhorat, et al., 1999). The cerebellar tissueoften appears asymmetric, with a flattened, beaked or rhomboid shape.

PURPOSETo describe the Chairi I Malformation in rela-tion to the anatomy of the brain and spinalcord, the common manifestations of the con-dition, diagnostic considerations, and manage-ment for the primary care provider.

DATA SOURCESExtensive review of the world-wide scientificliterature on the condition, supplemented withactual case studies.

CONCLUSIONSThe adult Chairi I Malformation is an insidi-ous congenital brainstem anomaly that con-sists of caudal displacement of the cerebellartonsils, brainstem and fourth ventricle into theupper cervical space, resulting in overcrowdingof the posterior fossa.

IMPLICATIONS FOR PRACTICEDue to the vague, and often ambiguous pre-senting symptoms of Chiari I Malformation,many patients are misdiagnosed with condi-tions such as multiple sclerosis, fibromyalgia,chronic fatigue syndrome, or psychiatric disor-ders. Patients frequently experience symptomsmonths to years prior to accurate diagnosis andoften incur irreversible neurologic deficits.

KEY WORDSChiari I Malformation; syringomyelia; syrinx.

AUTHORDiane Mueller, ND, RN, C-FNP, is aNeurosurgery Nurse Practitioner at theDivision of Neurosurgery, University ofMissouri Hospital and Clinics. Contact Dr.Mueller by e-mail at [email protected]

155 JOURNAL OF THE AMERICAN ACADEMY OF NURSE PRACTITIONERS

Adherence of the tonsils to the surrounding tissue is frequentlyevident on MRI. Obstruction of cerebral spinal fluid (CSF) flowfrom the fourth ventricle may result in hydrocephalus. Thedeformity is often associated with skull bone abnormalities, suchas basilar invagination. (Nishikawa, Sakamoto, Hakuba,Nakinshi, & Inoue, 1997). The malformation is present frombirth; however, for no clear reason, the symptoms generally donot present until the second to fourth decade of life. Althoughthe primary focus of this article is Chiari I Malformation, a briefdescription of the remaining types is offered for completeness.

Often associated with Chiari I Malformation is a syrinx orsyringomyelia. This is an abnormal cystic cavity of spinal fluidwithin the spinal cord. There are many theories postulatedregarding the origin or propagation of a spinal cord syrinx, how-ever no clear explanation of the etiology has been determined(Heiss et al., 1999; Milhorat, 2000). Spinal fluid normally flowsfrom the fourth ventricle, through the posterior fossa, and intothe spinal subarachnoid space with each cardiac cycle. Theoriessuggest that crowding of the posterior fossa by the impactedcerebellar tonsils leads to obstruction and abnormal pulsatileflow of CSF. This abnormal flow forces CSF from the obex intothe central area of the spinal cord, resulting in a syrinx.

Chiari II Malformation is considered a pediatric type, gen-erally presenting at birth. The deformity includes elongation ofthe cerebellar structures as well as the posterior fossa structures.The Chiari II Malformation is generally associated withmyelomeningocele or spina bifida occulta (Greenberg, 1994).

Chiari III Malformation generally presents at birth and isconsidered both rare and severe. This malformation is character-ized by caudal displacement of the cerebellar structures into acervical meningocele and carries a poor prognosis (Greenberg,1994).

Chairi IV Malformation is generally characterized byhypoplasia of the cerebellar tissue without the characteristicelongation of the cerebellar tonsils (Greenberg, 1994). Thisnomenclature is generally no longer used today.

ANATOMY AND PHYSIOLOGY OF THE CEREBELLUM

The brainstem, cerebellum and fourth ventricle lie within theposterior fossa. The predominant structure lying within the pos-terior fossa is the cerebellum. The cerebellum contains approxi-mately 50% of all neurons in the brain. The midbrain, contain-ing the cerebral peduncles, is the most rostral structure, lyinginferior to the diencephalon and superior to the pons. The cere-bellar tonsils are located on the underside of the cerebellum. Thenuclei of cranial nerves V, VI, VII, and VIII lie within the mid-brain and pons, making this a critical reflex area for cranial nervefunction. The corticospinal tract is composed of a large bundleof fibers that comprise the major motor pathway for the spinalcord. Connecting the third and fourth ventricles is the cerebralaqueduct, which traverses the midbrain. The cerebellum is asymmetric structure, composed of three major lobes: the floccu-lonodular lobe, the anterior lobe, and the posterior lobe.Afferent (sensory) and efferent (motor) nerve fibers lie withinthe three lobes (Kandel, Schwartz, & Jessell, 1991).

The functions of the cerebellum include coordination, equi-librium, and precision of movement. Gait, balance, posture, eyemovement and the planning and execution of volitional move-ments originate from the cerebellum. Disorders of the cerebellummanifest with clinical signs such as hypotonia, ataxia, abnormaleye movements, dysarthria, dysmetria, and dyssynergia.

CLINICAL MANIFESTATIONS

The patient with Chiari I Malformation can present with amyriad of ambiguous, inconsistent and often complex clinicalmanifestations, which may delay correct diagnosis. Subjectivesymptoms may be perplexing to the primary care providerbecause they are often transient or slowly progressive for monthsto years. Commonly, patients are misdiagnosed with neuromus-cular disorders such as multiple sclerosis, myasthenia gravis, orcervical myelopathy. Due to the vague, insidious symptoms,many patients are diagnosed with chronic fatigue, fibromyalgiaor psychiatric disorders, such as conversion reaction, neurosesand malingering. Most symptoms are related to compression of

Figure 1. Normal brain anatomy Figure 2. Chairi I Malformation with syringomyelia


the lower cranial nerves or brainstem structures. The followingare the most common clinical presenting symptoms:

Headache: One of the predominant presenting symptoms ischronic or progressively worsening headache (Dyste, Menezes,& VanGilder, 1989; Khurana, 1991; Mueller, 1999). Althoughnot clearly understood, theories suggest that cephalgia may bedue to obstruction of spinal fluid flow through the posteriorfossa into the spinal canal. The headache associated with ChiariI Malformation generally originates in the upper cervical region,or the suboccipital area. Pain generally radiates throughout theposterior-occipital region, to the vertex and into the frontal andperiorbital areas. The headache is often described as pressure, ordiffuse fullness. Coughing, sneezing, bending forward, laughingor valsalva maneuvers often precipitate or worsen the pain.Duration of the pain can be minutes to days. Many patientsreport a constant headache that is unrelieved with medications.Associated nausea can occur, but vomiting is less frequent.

Neuro-ophthalmologic manifestations: Visual disturbancesincluding nystagmus, diplopia, blurred vision, scotoma, andamaurosis fugax are common occurrences and may be due topressure on the cranial nerves from herniation of the cerebellartonsils (Chait, & Barber, 1979; Faria, Spector, & Tindall, 1980;Weber, & Cass, 1993). Patients may complain of vague inter-mittent visual changes or periods of complete vision loss.Nystagmus, or downbeat nystagmus, is often described by thepatient as “bobbing of the eyes” on vertical or lateral gaze. Thepatient may also report difficulty reading and driving due toblurred vision.

Dysphagia: Swallowing difficulty and neurogenic dysphagiaare symptoms that can be rapidly progressive and lead to aspira-tion if undetected (Elta, Caldwell, & Nostrant, 1996;Nathadwarawala, Richards, Lawrie, Thomas, & Wiles, 1992;Pollack, Pang, Kosochis, & Putnam, 1992). Dysphagia is one ofthe cardinal signs of compression of the cerebellum and lowercranial nerves. Patients may report difficulty swallowing eithersolids or liquids or a sensation of “catching” in the throat. Earlydetection of dysphagia is imperative to prevent aspiration andthe associated sequella.

Pain: The pain associated with Chiari I Malformation maybe diffuse, localized, mild or severe (Milhorat et al., 1999). Theexact cause of the pain is uncertain. Alteration or obstruction inspinal fluid flow contributes to pressure on the nerve roots.Patients may complain of pain in the face, neck, or extremitiesand may describe the sensation as dull, aching, shooting, or stab-bing. The pain associated with Chiari I Malformation is one ofthe most difficult symptoms to assess due to its diffuse, vaguenature, and ambiguous dermatomal distribution. In general,unilateral pain is more commonly reported than bilateral pain.

Weakness: Some patients may also experience weakness ofthe upper or lower extremities. Characteristics of a central cordsyndrome may result from alteration in spinal fluid flow. If sig-nificant or episodic weakness of an extremity is detected, thepossibility of a syringomyelia (or abnormal fluid cavity) shouldbe considered (Heiss et al., 1999).

Sensory disturbances: Parasthesias, numbness, dysesthesia,or proprioceptive disturbances can also accompany pain in theface, lips, or extremities. Numbness is generally unilateral and

often begins distally. Facial numbness can occur acutely andbecome transient in nature. Peripheral extremity numbness canbe slowly progressive over months to years or can occur acutely.The patient may report burning or cutaneous injury of anextremity without knowledge of the event. A syringomyeliashould be considered in any person with progressive sensory loss(Cahan, & Bentson, 1982; Guyotat, Bret, Jouanneau, Ricci, &Lapras, 1998).

Hoarseness: Change in character or timbre of the voice is acommon complaint and is thought to be the result of compres-sion of the ninth and tenth cranial nerves. The patient may com-plain of inability to modulate the voice for singing or speaking.A family member or partner will often notice voice changes first.Slurred speech has also been reported, with the patient describ-ing a “thick tongue” and intermittent inability to enunciateclearly.

Ataxia or gait disturbances: Gait disturbance or dysequilib-rium are frequently reported by the patient and are generally theresult of cerebellar compression due to herniation of the tonsils,or ensuing hydrocephalus. Many patients complain of dizziness,with a resultant gait disturbance. Infrequently, patients may pre-sent with spasticity or atrophy of the lower extremities, whichimplies upper and lower motor neuron involvement. For theseindividuals, hyperactive reflexes and loss of sensory discrimina-tion may indicate a central cord syndrome or spinal cord syrinx(Dyste, Menezes, & VanGilder, 1989; Mueller, 1999).

Dizziness: Many patients complain of dizziness, often pre-cipitated or worsened with straining or bending forward. This isdue to compression of the cerebellum as well as altered spinalfluid flow. Dizziness can often result in gait instability, leading tofrequent falls and possible injury. Patients may also complain oftransient vertigo. Because of these symptoms, many patients aremis-diagnosed with Meniere’s Disease or inner ear infections.

Syncope: Syncopal episodes are a less common manifestationof Chiari I Malformation and are most often associated withsyringomyelia (Weig, Buckthal, Choi, & Zellem, 1991;Hampton, Williams, & Loizou, 1982). The syncopal episodesare paroxysmal and brief, generally lasting from seconds to min-utes. There is often an associated alteration in level of conscious-ness, but no evidence of seizure or post-ictal type symptoms.

Respiratory changes: The respiratory changes occurring withChiari I Malformation include apnea, sleep apnea, and shortnessof breath unrelated to exertion. Alterations in respiratory statusare again the result of compression of the cerebellum and alter-ation in spinal fluid flow. Many patients complain of chest heav-iness, or insufficient inspiratory volume, resulting in shortness ofbreath. Some will report frequent sleep apnea spells, particularlywhen supine.

Generalized body weakness: Generalized body weakness andincreased fatigue are frequent complaints among patients withChiari I Malformation. They may report decreased ability toremain active for any duration of time and often report inabilityto complete routine activities. Due to these complaints, manyare misdiagnosed with Chronic Fatigue Syndrome.

Other associated symptoms: A number of other vague, andoften transient symptoms may be reported by the patient.Depression is common, and lack of involvement in previous


interests ensues. The patient often reports inability to participatein activities, thus adversely affecting perceived quality of life.Transient, unexplained epistaxis may be reported. Unexplainedparoxysmal bradycardia, or tachycardia, and blood pressurechanges (both hypertension and hypotension) have been report-ed and are generally refractory to pharmacologic treatment.Tinnitus or decreased hearing, either unilateral or bilateral havealso been described.

ASSESSMENT AND DIAGNOSTIC TESTS

When assessing the patient with possible Chiari IMalformation, it is imperative to perform a thorough history andphysical examination with emphasis on the neurologic system.Key portions of the neurologic examination include cerebellarfunctions, sensory evaluation, and cranial nerve testing (Table 1).

Many patients exhibit very subtle, focal neurologic deficits; somemay have a completely normal neurologic examination.

Prior to the advent of MRI, the diagnosis of Chiari IMalformation was based on clinical conjecture, neurologic eval-uation, and possibly myelography of the cervical spine and cran-iocervical junction. Currently, the neuroradiologic test of choicein the diagnostic evaluation for Chiari I Malformation is a non-contrast MRI of the brain and brainstem (Aboulezz, Sartor,Geyer, & Gado, 1985; Elster, & Chen, 1992; Pujol et al., 1995).The purpose of the MRI is to demonstrate the extent of cerebel-

l a rh e r -n i a -t i on ,t h e

appearance of the tonsils, and the amount of brainstem com-pression (Image 1). Using T1 and T2 weighted images, the MRIwill also demonstrate evidence of hydrocephalus or other lesionswithin the brain and brainstem. An MRI of the cervical spinemay demonstrate an associated syringomyelia (Image 2).Another option for neuroimaging is the phase-contrast cine MRI(Pujol et al., 1995). This test demonstrates the flow of CSF

Table 1. Essentials of the Neurologic Examination

Cerebellar Functions:RombergFinger-to-noseHeel-to-shinGait and tandem gaitRapid alternating movements

Sensory evaluation:ProprioceptionLight touch, pinprickHot/coldVibratory sense

Cranial Nerve Tests:I - smell soap, coffee, alcohol (never use ammonia)II - visual acuity, visual fields, fundoscopic examIII, IV, VI - extra ocular movements, pupil response to lightV - blink reflexVII - smile, wrinkle brow, grimaceVIII - hearing- finger rub, Rinne, Weber’s testIX, X - gag reflex, swallow, tongue, uvula and palateXI - shoulder shrugXII - tongue movement and symmetry

Image 1. Preoperative sagittal magnetic resonance imagedemonstrating tonsillar herniation below the level of theforamen magnum. Note the elongated, or beaked shape of the tonsils.

Image 2. Preoperative sagittal magnetic resonance imagedemonstrating tonsillar herniation below the level of theforamen magnum and large syringomyelia extendinginto the thoracic spinal cord.


through the craniovertebral junction and caudally past the cere-bellum. Conventional computerized tomography (CT) general-ly lacks the sensitivity to show sufficient detail of the cerebellartissue. However, for those patients who are claustrophobic or areunable to undergo MRI scanning, a thin-cut CT of the cran-iovertebral junction visualizing to cervical two, angled to thebasion and opisthion with sagittal reconstructions, can provideinformation regarding the amount of space in the posterior fossa.

TREATMENT

Once the diagnosis of Chiari I Malformation has been estab-lished, treatment options may be discussed. Prompt referral to aneurosurgeon is indicated for patients with evidence of Chiari IMalformation on MRI, particularly for those with evidence ofneurologic deficit. Surgical decompression of the posterior fossaby a neurosurgeon is generally regarded as the treatment ofchoice (Bindal, Dunkser, & Tew, 1995; Guyotat, Bret,Jouanneau, Ricci, & Laprat, 1998). The goal of surgical inter-vention is to decompress the foramen magnum and enlarge theposterior fossa space, thereby attempting to normalize CSF flow.Although there is some controversy about the specific operation,the general procedure is as follows: Under general anesthesia, thepatient is placed prone, with the head generally supported in athree pin device. A midline incision is made from the inion toapproximately cervical two. The area is retracted and dissectioncontinues to achieve adequate visualization of the suboccipitalregion. A laminectomy is generally performed on the first cervi-cal vertebrae, and the posterior fossa bone is thinned. An inci-sion is made in the dura to expose the tonsils. Fine electrocauterymay be used to further decompress (or shrink) the tonsils (Won,Nambiar, Muszynski, & Epstein, 1997). If a membrane of tissueis found to block the foramen of Magendie, this may be fenes-trated in an effort to reestablish normal flow of CSF. In order topermit additional space in the dura for the cerebellar tissue, andto attempt to allow adequate space for spinal fluid pathway, apatch graft or duraplasty is constructed. The patch graft is sewnonto the existing dura to form a wider area in the posterior fossa.The tissue used for duraplasty may be either synthetic material,bovine pericardium, or periosteum (Vanachocha, & Saiz-Sapena,1997).

POST-OPERATIVE CARE AND FOLLOW-UP

In the immediate post-operative phase, most patients areplaced on a patient-controlled analgesic (PCA) pump and anti-inflammatory medications for pain control. Due to the highincidence of post-operative nausea, patients are given antiemet-ics to decrease the incidence of emesis. Although the risk of dev-astating neurologic damage is low, close observation of the neu-rologic status is imperative, particularly in the first 24 hours. Thehospital stay is generally 3-5 days.

The frequency of follow-up clinic appointments depends onthe initial clinical findings, as well as the patient’s progress after

surgery. Generally, most patients are evaluated in the neurosurgeryclinic at one month intervals until three months post-operatively.Clinic visits may be more frequent as the patient’s condition war-rants. A follow-up MRI is obtained at 3-6 months to evaluate sur-gical healing, and reevaluate the status of previous syrinx.

PROGNOSIS

Although no systematic, long-term follow-up data have beenreported, early results indicate that those patients without evi-dence of syrinx see improvement in most or all of their previoussymptoms after decompression surgery. In retrospective reviews,patients without evidence of pre-operative neurologic deficit andno syrinx, improved in either all or most of their symptoms(Bindal, Dunkser, & Tew, 1995; Guyotat, Bret, Jouanneau,Ricci, & Lapras, 1998). Those patients with large syrinx and pre-operative neurologic deficits may see gradual improvement overmonths to years. Early detection and treatment appears to posi-tively affect outcome.

CASE EXAMPLE I:

A 25-year old, healthy male presented with a one-year histo-ry of progressively worsening headache, unresponsive to medica-tions. The headache was described as throbbing and sharp, orig-inating in the posterior occipital area, and radiating through thebi-temporal areas. He also reported hoarseness and inability tomodulate his voice. Clinical examination revealed no neurologicdeficits, and no focal findings. Initially he did not have an MRIand was treated symptomatically with medications for over oneyear by his primary care provider. After progressive symptoms forone year, an MRI was performed. The MRI of the brain andbrainstem revealed approximately 5mm tonsillar herniation withno evidence of syrinx. He elected to undergo posterior fossadecompression. At three months post-operatively he noted com-plete resolution of the pre-operative symptoms.

CASE EXAMPLE II:

A 43-year old healthy male presented with a history of mul-tiple neurologic complaints that had progressively worsened overthe previous ten years. Prior to consultation, he was diagnosedand treated by his primary care provider for multiple sclerosis.He reported bilateral tinnitus, and acute right side hearing loss,occasional difficulty swallowing, transient left face and tonguetingling, and acute left arm pain. He denied headaches, visionchanges, apnea, or dizziness. Neurologic examination revealeddecreased hearing on the left to finger-rub, otherwise no focalfindings. The MRI of the brain and brainstem revealed approx-imately 12 mm tonsillar herniation with no evidence of MSlesions or syringomyelia. Posterior fossa decompression was per-formed with resolution of all symptoms, with the exception ofright tinnitus, within six months post-operatively.


CASE EXAMPLE III:

A 45-year old healthy woman noted acute onset of difficultyswallowing, and choking at night for approximately two weeks.She reported transient mild neck pain over the previous ten years,and transient tingling of the left upper and lower extremity.History was negative for headache, dizziness, vision or hearingchanges. A barium swallow was performed by her primary careprovider, revealing aspiration of both liquids and solids. A subse-quent MRI was performed to rule out cerebrovascular accidentCVA. The MRI revealed approximately 18 mm tonsillar hernia-tion. Five days after posterior fossa and cervical one decompres-sion, her gag reflex and swallowing had improved. At six weeks,all of her pre-operative symptoms had completely resolved.

SUMMARY

Chiari I Malformation is an insidious neuroskeletal disorderthat consists of caudal displacement of the cerebellar structures.Patients may present with a myriad of vague, and often confus-ing symptoms, which are often misdiagnosed. Patients present-ing with this disorder may be a challenge to the primary careprovider. With early detection of the disorder, a timely andappropriate treatment plan can be implemented, thereby ensur-ing a favorable outcome and preventing permanent neurologicdeficit or deterioration.

ReferencesAboulezz, A.O., Sartor, K., Geyer, C.A., & Gado, M.H. (1985). Position of cerebel-

lar tonsils in the normal population and in patients with Chiari Malformation:a quantative approach with MR imaging. Journal of Computer AssistedTomograhpy, 9(6), 1033-1036.

Bindal, A.K., Dunsker, S.B., & Tew, J.M. (1995). Chiari I Malformation:Classification and management. Neurosurgery, 37(6), 1069-1074.

Cahan, L.D., & Bentson, J.R. (1982). Considerations in the diagnosis and treat-ment of syringomyelia and the Chiari malformation. Journal ofNeurosurgery, 57, 24-31.

Carmel, P.W., & Markesbery, W.R. (1972). Early descriptions of the Arnold-Chiarimalformation. Neurosurgery, 37, 543-547.

Chait, G.E., & Barber, H.O. (1979). Arnold-Chiari malformation: some otoneuro-logical features. Journal of Otolaryngology, 8, 65-70.

Dyste, G.N., Menezes, A.H., & VanGilder, J.C. (1989). Symptomatic ChiariMalformations: an analysis of presentation, management, and long-termoutcome. Journal of Neurosurgery, 71, 159-168.

Elster, A.D., & Chen, M.Y. (1992). Chiari I Malformations: clinical and radiologicreappraisal. Radiology, 183(2), 347-353.

Elta, G.H., Caldwell, C.A., & Nostrant, T.T. (1996). Esophogeal dysphagia as thesole symptom in Type I Chiari malformation. Digestive Diseases andSciences, 41 (3), 512-515.

Faria, M.A., Spector, R.H., & Tindall, G.T. (1980). Downbeat nystagmus as thesalient manifestation of the Arnold-Chiari malformation. Surgical Neurology,13, 333-336.

Greenberg, M.S. 1994. Handbook of Neurosurgery, Lakeland, FL: GreenbergGraphics.

Guyotat, J., Bret, P., Jouanneau, E., Ricci, A.C., & Lapras, C. (1998).Syringomyelia associated with Type I Chiari Malformation: a 21 year retro-spective study on 75 cases treated by Foramen Magnum decompressionwith a special emphasis on the value of tonsils resection. Acta Neurochir(Wien), 140, 745-754.

Hampton, F., Williams, B., & Loizou, L. (1982). Syncope as a presenting featureof hindbrain herniation with syringomyelia. Journal of Neurology,Neurosurgery and Psychiatry, 45, 919-922.

Heiss, J.D., Patronas, N., DeVroom, H.L., Shawker, T., Ennis, R., Kammerer, W.,Eidsath, A., Talbot, T., Morris, J., Eskioglu, E., & Oldfield, E.H. (1999).Elucidating the pathophysiology of syringomyelia. Journal of Neurosurgery,91, 553-562.

Kandel, E.R., Schwartz, E.R., & Jessell, T.M. (1991). Principles of NeuralScience. (3rd ed.). New York: Elsevier Science Publishing Co., Inc.

Khurana, R.K. (1991). Headache spectrum in Arnold-Chiari malformation.Headache, 31, 151-155.

Milhorat, T.H. (2000). Classification of syringomyelia. Neurosurgery Focus, 8(3), 1-6.Milhorat, T.H., Chou, M.W., Trinidat, E.M., Kula, R.W., Mandell, M., Wolpert, C., &

Speer, M.C. (1999). Chiari I Malformation redefined: clinical and radiograph-ic findings for 364 symptomatic patients. Neurosurgery, 44(5), 1005-1017.

Mueller, D.M. (1999, September) Cervical Conundrum, [available on-line athttp://www.hsc.missouri.edu/~shrp/vhstwww/case1799]

Nathadwarawala, K.M., Richards, C.A., Lawrie, B., Thomas, G.O., & Wiles, C.M.(1992). Recurrent aspiration due to Arnold-Chiari type I malformation.British Medical Journal, 304, 565-566.

Nishikawa, M., Sakamoto, H., Hakuba, A., Nakinishi, N., & Inoue, Y. (1997).Pathogenesis of Chiari malformation: a morphometric study of the posteri-or cranial fossa. Journal of Neurosurgery, 86, 40-47.

Paul, K.S., Lye, R.H., Strang, F.S., & Dutton, J. (1983). Arnold-Chiari malforma-tion: review of 71 cases. Journal of Neurosurgery, 58, 183-187.

Pollack, I.F., Pang, D., Kocoshis, S., & Putnam, P. (1992). Neurogenic dysphagiaresulting from Chiari malformations. Neurosurgery, 30(5), 709-719.

Pujol, J., Roig, C., Capdevila, A., Pou, A., Marti-Vilalta, J.L., Kulisevshy, J.,Escartin, A., & Zannoli, G. (1995). Motion of the cerebellar tonsils in Chiaritype I malformation studied by cine phase-contrast MRI. Neurology, 45,1746-1753.

Vanachocha, V., & Saiz-Sapena, N. (1997). Duraplasty with freeze-dried cadav-eric dura versus occipital pericranium for Chiari type I Malformation: com-parative study. Acta Neurochir (Wien), 139, 112-119.

Weber, P.C., & Cass, S.P. (1993). Neurotologic manifestations of Chiari I malfor-mation. Otolaryngology- Head and Neck Surgery, 109(5), 853-860.

Weig, S.G., Buckthal, P.E., Choi, S.K., & Zellem, R.T. (1991). Recurrent syncopeas the presenting symptom of Arnold-Chiari malformation. Neurology, 41,1673-1674.

Won, D.J., Nambiar, U., Muszynski, C.A., & Epstein, F.J. (1997). Coagulation ofherniated cerebellar tonsils for cerebrospinal fluid pathway restoration.Pediatric Neurosurgery, 27, 272-275.

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Brainstem Conundrum: The Chiari I Malformation