Arnold-Chiari malformation

Arnold-Chiari Malformation: A Diagnostic Challenge Arnold-Chiari malformation is a disorder of embryologic development. In Type I, there is cerebellar displacement into the spinal canal, but hydrocephalus and syringomyelia are variable. Type II usually is manifested by severe hydrocephalus and myelomeningocele in infancy. Type I malformations may pose diagnostic challenges because they often produce bizarre and vague symptoms. A careful history and physical examination, coupled with neurologic testing, especially magnetic resonance imaging, will lead to the correct diagnosis. In 1883, John Cleland, a British poet and anatomist, first described the abnormality of the brainstem and cerebellum we now call Arnold-Chiari malformation. Chiari in 1891 and Arnold in 1894 further detailed this anomaly in children with hydrocephalus, but it was not until 1907 that students of Arnold coined the term "Arnold-Chiari malformation."

Arnold-Chiari malformation consists of migration of the brainstem and cerebellum into the spinal canal. There are two types (Table 1). In Type I, the cerebellum extends downward through the foramen magnum. Associated abnormalities may include hydrocephalus and syringomyelia or cavitation within the spinal cord.

In addition to the features of Type I, Type II is characterized by elongation of the fourth ventricle into the spinal canal, displacement of the medulla and crowding of the cervical cord roots into an upward course. Severe hydrocephalus along with myelomeningocele is usually apparent. Kinking of the medulla at the cervicomedullary junction is present in over 50 percent of cases.(1,2)

The etiology of these developmental abnormalities is controversial. Caudal fixation of the cord and traction on the brainstem may play a role. Some investigators suggest the importance of abnormal fluid pressures within the developing neural tube. Another etiologic possibility may be overexpansion of the nervous system within the bony vertebrae.(1,2)

Illustrative Cases

This article describes two patients with Arnold-Chiari Type I malformations. While this disorder is rare, these cases underscore three important points for primary care physicians: the need to evaluate the origin of vague and bizarre symptoms that may initially suggest a psychiatric disorder, the need to remain vigilant about the possibility of other diagnoses even though a specific diagnosis has been made, and the need to utilize new information and new technology as they arise.

CASE 1

A 45-year-old right-handed woman presented to the family practice clinic with a presumed exacerbation of multiple sclerosis, which had been diagnosed in 1980. Her symptoms included recurrence of rotatory nystagmus, intermittent diplopia and severe fatigue. During the ensuing years, she experienced relapses of these symptoms every few months, with exacerbations lasting from one to two weeks. She also reported associated depression.

The current examination was remarkable only for rotatory nystagmus. The remainder of the neurologic examination was within normal limits. Since the woman was a new patient in the family practice clinic, it was elected by both the physician and the patient to obtain a neurologic consultation.

Examination by the neurologist revealed normal funduscopy with spontaneous venous pulsations. Visual fields were intact. Pupils were equally round and reactive to light both directly and consensually. Extraocular muscles were intact. The patient exhibited a prominent rotatory nystagmus, but otherwise cranial nerves II through XU were intact. Motor examination was normal. Babinski's response was absent bilaterally. Cerebellar testing was normal, as was the patient's gait.

The neurologist's impression was of an ill-defined central nervous system disease with symptoms atypical of multiple sclerosis. The differential diagnosis included various causes of chronic labyrinthine dysfunction or chronic processes affecting the vestibular nuclei in the brainstem, as well as a mass lesion in the posterior fossa or an Arnold-Chiari Type I malformation. The consultant recommended a review of all of the patient's past medical records, including the allegedly normal cerebrospinal fluid (CSF) examination. If this review failed to support the diagnosis of multiple sclerosis, he recommended magnetic resonance imaging (MRI). No confirmatory evidence of multiple sclerosis was uncovered on analysis of the patient's medical records.

MRI of the brain was performed, which revealed an Arnold-Chiari Type I malformation. Cerebellar tonsillar herniation was present to the level of C2 in both the sagittal and axial projections. Angulation of the medulla was noted at the cervicomedullary junction, with some compression. Syringomyelia was not present.

The patient subsequently underwent posterior fossa and upper cervical decompression with`placement of a dural patch graft. Neurologic examination six months postoperatively was normal; rotatory nystagmus was absent. The patient related that she was able to resume many activities that she had been forced to give up when she was thought to have multiple sclerosis.

CASE 2

A 42-year-old right-handed woman presented to the family practice clinic for evaluation of weakness of her left arm. Her symptoms had begun five months previously, when she noted difficulty in picking up her daughter. Her symptoms had gradually progressed to the point where she was having trouble opening jars and was dropping things. She denied pain, numbness or paresthesia in either her left hand or arm.

The patient's past medical history was significant in that she had undergone radical mastectomy and reconstructive surgery for carcinoma of the left breast approximately two and one-half years previously. Local recurrence in the chest wall was noted six months postmastectomy and was treated with local irradiation.

Neurologic examination demonstrated no abnormalities of cranial nerves II through XII. Funduscopic examination was within normal limits and visual fields were intact to confrontation. The pupils were equally round and reacted to light both directly and consensually. Extraocular muscles were intact. Hearing was judged to be grossly intact. Sensory examination demonstrated impaired pin prick perception over the entire left arm and also a portion of the left thorax. The sensory changes over the thorax, however, were thought to be inconsistent. Vibratory and position senses were impaired on the left side. Motor examination showed diffuse weakness of the left arm, which involved the deltoid, wrist flexor and intrinsic hand muscles. Deep tendon reflexes were 2+/4 and equal throughout. Babinski's response was absent. Cerebellar testing was intact and gait was normal.

The neurologic consultant felt that an organic lesion might be present in view of the patient's history of locally recurrent breast carcinoma. Diagnostic possibilities presented by the neurologist included radiation-induced damage of the left brachial plexus, a metastatic lesion involving the left brachial plexus or, possibly, a metastatic lesion of the right cerebral hemisphere. Recommendations for the diagnostic work-up included MRI of the brain and left brachial plexus area.

MRI demonstrated an Arnold-Chiari Type I malformation, as well as a 2-cm by 1-cm central cystic area at the level of C2-C3. It was felt that the cystic area most likely represented syringohydromyelia; however, a cystic tumor could not be totally excluded. No other abnormalities were identified in either the cervical spine or brain.

The patient subsequently underwent a posterior fossa and upper cervical decompression procedure with drainage of the syrinx and placement of a dural patch graft. Six months postoperatively, the patient had regained much of her left arm function. She still has some pain in her arm, but the pain will probably resolve gradually.

Clinical Presentation

The presentation of Arnold-Chiari Type II malformation is usually striking and early in life.(3) Affected infants exhibit congenital hydrocephalus and myelomeningocele, and stridor, apnea and feeding difficulties are early problems. Older children may show abnormal eye movements, cranial nerve palsies and weakness.

In contrast, Type I malformations usually do not become symptomatic until adulthood, when affected patients present with vague, puzzling symptoms.(4-7) The average age at presentation is 40 years. Males and females are equally affected. The onset of symptoms precedes the diagnosis by an average of five to ten years. Headaches, cervical pain and sensory complaints are present in at least 50 percent of patients. Upper extremity weakness, gait disturbances, dysfunction of cranial nerves IX through XII, blurred vision and lower extremity weakness occur less commonly.

The most common abnormalities on physical examination are motor changes indicative of central cord or long-tract involvement. Signs of brainstem compression, such as cranial nerve dysfunction, and sensory abnormalities are also common. Nystagmus, ataxia and other cerebellar abnormalities, and signs of increased intracranial pressure occur less frequently.

Because of the protracted and vague nature of the symptoms, misdiagnosis is common. Symptoms and signs are often attributed to multiple sclerosis, amyotrophic lateral sclerosis, cervical spine problems, post-traumatic syndromes or psychiatric disorders.(7,8) A careful history and neurologic examination are crucial for diagnosis.

Clues to the diagnosis of Arnold-Chiari Type I malformation include the prolonged, persistent and progressive nature of the patient's complaints and the presence of subtle but important findings on neurologic examination. Analysis of the CSF (especially for IgG), myelography and computed tomographic scanning will often narrow the diagnosis. MRI has now become the key to diagnosis of this malformation, because this study can demonstrate the demyelination of multiple sclerosis, can provide a picture of the posterior fossa and craniovertebral junction, and can demonstrate unsuspected syrinxes.

Treatment

The treatment of Arnold-Chiari malformation is usually surgical.(3-6) With Type II, shunting for hydrocephalus and repair of the myelomeningocele are priorities. For both types, decompression laminectomy is the operation of choice. Plugging of the central canal, aspiration of syrinx fluid and shunting may be therapeutic in selected cases.

The long-term outlook is usually guarded, especially when a syrinx or central cord syndrome is initially present. Infants with Type II malformation have a grave prognosis because of involvement of vital nervous system structures.

Final Comment

Although the Arnold-Chiari malformation is a rare disorder, several important points bear emphasis. First, symptoms that seem vague and bizarre may nonetheless represent the onset of organic disease. It is imperative for the physician to evaluate such complaints objectively and reassess the patient when symptoms are persistent or progressive. Second, even with a secure diagnosis, reevaluation should be routine in light of new symptoms or technology. The recent introduction of MRI, for instance, may play a key role in differentiating multiple sclerosis, Arnold-Chiari malformations and other nervous system disorders.

TABLE 1

Characteristics of Arnold-Chiari Malformation

spinal canal

at the cervicomedullary junction

PHOTO : Case 1: Magnetic resonance imaging shows herniation of the cerebellar tonsils below the

PHOTO : level of the first cervical vertebra (arrow), consistent with Arnold-Chiari Type I

PHOTO : malformation.

PHOTO : Case 2: Magnetic resonance imaging demonstrates herniation of the cerebellar tonsils

PHOTO : (black arrow) and syringohydromyelia (white arrow), consistent with Arnold-Chiari Type I

PHOTO : malformation. REFERENCES (1)Schut L, Bruce DA. The Arnold-Chiari malformation. Orthop Clin North Am 1978;9:913-21. (2)Raynor RB. The Arnold-Chiari malformation. Spine 1986;11:343-4. (3)Bell WO, Charney EB, Bruce DA, Sutton LN, Schut L. Symptomatic Arnold-Chiari malformation: review of experience with 22 cases. J Neurosurg 1987;66:812-6. (4)Paul KS, Lye RH, Strang FA, Dutton J. Arnold-Chiari malformation. Review of 71 cases. J Neurosurg 1983;58:183-7. (5)Levy WJ, Mason L, Hahn JF. Chiari malformation presenting in adults: a surgical experience in 127 cases. Neurosurgery 1983;12:377-90. (6)Eisenstat DD, Bernstein M, Fleming JF, Vanderlinden RG, Schutz H. Chiari malformation in adults: a review of 40 cases. Can J Neurol Sci 1986;13:221-8. (7)Kumar A, Jafar J, Mafee M, Glick R. Diagnosis and management of anomalies of the craniovertebral junction. Ann Otol Rhinol Laryngol 1986;95(5 Pt 1):487-97. (8)Rudick RA, Schiffer RB, Schwetz KM, Herndon RM. Multiple sclerosis. The problem of incorrect diagnosis. Arch Neurol 1986;43:578-83.

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