Cerebellopontine angle arachnoid cyst associated with mirror movements.

Arachnoid cysts are benign developmental collections of cerebrospinal fluid (CSF). They constitute approximately 1% of intracranial masses. The cerebellopontine angle (CPA) arachnoid cysts are rare and often asymptomatic. The onset of symptoms and signs is usually due to the compression of the brain, cranial nerves and obstruction of CSF circulation. The major clinical symptoms for CPA arachnoid cysts were reported as headache, ataxia and 8(th) cranial nerve palsy. We report a patient with a CPA arachnoid cyst. He presented with cranial nerve palsies and mirror movements found in upper extremities. We postulated that CPA arachnoid cyst compressing the brain stem and the pyramidal decussation may lead to mirror movements. We conclude that mirror movements can be associated with CPA arachnoid cyst.

Introduction

Arachnoid cysts are benign developmental collections of cerebrospinal fluid (CSF) contained within the arachnoid membrane. Middle cranial fossa is the most common site of occurrence, followed by the cerebellopontine angle (CPA) and suprasellar area. The arachnoid cysts of CPA usually remain asymptomatic so they are often diagnosed incidentally during radiological evaluation for other reason.[1] But they can expand and may cause signs and symptoms by compressing surrounding neural structures or increasing intracranial pressure.

We report a patient with CPA arachnoid cyst presenting with cranial nerve palsies and mirror movements caused by the compression of the brain stem. To our knowledge, this is the first case with mirror movements associated with an arachnoid cyst of CPA.

Case Report

A left-handed 13-year-old boy presented to our pediatric neurology unit with complaints of right facial weakness for 1 day and abnormal hand movements since early childhood. Because of his family's socioeconomic problems, he didn't go to any doctor for abnormal hand movements. He had simultaneous involuntary movements of one hand associated with the voluntary movements of the other hand.

He was born of nonconsanguineous parents as a preterm infant at 36th weeks of gestation. His developmental milestones were a little bit late according to his peers. He had a febrile seizure at 18th months of age. There was no family history of similar illness, epilepsy or mental disease.

On his neurological examination, the pupils were isochoric, direct and indirect pupil reflexes were normal. There was limited abduction on the right eye. He had right facial weakness. So on neurological examination, 6th, 7th cranial nerve palsies were found. He had also mirror movements on both upper extremities and had intentional tremor on right hand.

Magnetic resonance imaging (MRI) of the brain revealed a cystic lesion isointense with CSF on all sequences (hypointense on T1-weighted and hyperintense on T2-weighted images) at anteroinferior of the right cerebellar hemisphere, extending to right CPA cistern [Figures 1 and 2]. It was causing compression of right cerebellar hemisphere and brain stem. The findings of the MRI were consistent with arachnoid cyst. The patient was referred to pediatric neurosurgery department. Fenestration operation was planned but the patient's family refused further investigation. For this reason, surgery could not be performed.

Figure 1

Axial T2-weighted magnetic resonance imaging scan showing an arachnoid cyst located in the right cerebellopontine angle

Figure 2

Coronal T2-weighted magnetic resonance imaging scan showing the arachnoid cyst with the compression of the brain stem

Discussion

Arachnoid cysts constitute approximately 1% of all nontraumatic intracranial space-occupying lesions.[2] Arachnoid cysts may be congenital or secondary to trauma, tumor or infection.[3] The majority of the arachnoid cysts seen in children are congenital. Our patient had no previous history to suggest an etiology other than congenital and therefore we considered it as a congenital cyst.

Arachnoid cysts in the CPA are often asymptomatic. They may become symptomatic because these cysts may gradually increase in size. The onset of symptoms and signs is usually due to the compression of the brain, cranial nerves and obstruction of CSF circulation. The major clinical symptoms for CPA arachnoid cysts were reported as headache and ataxia. Also patients have presented with nausea, vomiting, cerebellar signs, character change, memory disturbance.[4] These cysts also can cause dysfunction of specific cranial nerves, including III, IV, VI (to cause diplopia), V (to induce trigeminal neuralgia), VII (to cause congenital or acquired facial paralysis), VIII (to cause hearing loss, tinnitus, vertigo), X (to result in hoarseness and dysphagia).[567] Also our patient had VI, VII cranial nerve palsies and intentional tremor due to cerebellar compression. Mirror movements are involuntary movements, which occur in a muscle group or limb on one side of the body in response to an intentionally performed movement in corresponding contralateral muscle group or limb.[8] Mirror movements have been classified into three categories. Physiologic form often presents at birth, and disappears along with the maturation of the nervous system by the age of 8–10 years. In hereditary form, heterozygous mutations of DCC gene were shown.[9] Pathologic form can be clinically isolated or associated with nervous system disorders. Klippel–Feil syndrome is the commonest disease associated with the mirror movements. The other disorders are Kallmann's syndrome, agenesis of corpus callosum, basilar invagination of the skull, spina bifida occulta, Arnold–Chiari type I malformation, Friedrich's ataxia, Usher syndrome, Seckel syndrome, hemiplegic cerebral palsy.[1011] The exact pathophysiology of mirror movements is not known. Abnormal interhemispheric inhibition between two motor cortices, functional alteration of motor planning and motor execution and/or abnormal persistence of the ipsilateral tract may be involved in the pathogenesis of mirror movements.[9] In our case, lots of etiologies may be the cause of mirror movement. It may be physiologic but our patient is 13 years old and still has these movements. We expect the disappearance of mirror movements by the end of first decade if it is physiologic. There is no family history of such mirror movements in our case, however it may be hereditary. But mirror movements in our patient could also be associated with CPA arachnoid cysts. We postulated that CPA arachnoid cyst compressing the brain stem and the pyramidal decussation may lead to aberrant development of the neural pathways and mirror movements. Our hypothesis is supported by previous reports, in which mirror movements were seen in patients with brainstem compression.[1011] We cannot conclude that there is a causal relationship between CPA arachnoid cysts and mirror movements, but we can say that there may be an association between these two conditions.

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Conflicts of interest

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