Not all cases of nyctalopia are benign: Unusual and serendipitous presentation of Arnold-Chiari Type 1 malformation at a Pediatric Tertiary Care Center.

The Arnold-Chiari Type 1 malformation (CM1) is a rare congenital abnormality characterized by ectopia or caudal herniation of the cerebellar tonsils through the foramen magnum into the cervical spine, resulting in crowding at the craniocervical junction. It seldom presents in childhood with symptoms and a normal neurological examination. More typically, CM1 presents in young adult women with neurological symptoms including a headache, cervical pain, cranial nerve palsies, neurosensory deficit, and ataxia. Ocular manifestations associated with Chiari I include third and sixth cranial nerve paresis and convergence/divergence abnormalities. Papilledema is a rare manifestation of Chiari I with a clinical presentation often similar to that of idiopathic intracranial hypertension. To underscore this noteworthy complication, the authors report a case of an 8-year-old boy who presented with nyctalopia and suboccipital headaches, but was diagnosed serendipitously as a case of papilledema due to Chiari I malformation.

Introduction

Chiari malformation is a significant hindbrain deformity that is subdivided into Types 0 through 4.[1234] Types 1 and 2 are of greater clinical importance than Types 0, 3, and 4. The prevalence rate of this disorder is estimated to be 0.1–0.5%, with a slight female predominance seen in recent studies.[56] Based on the analysis of familial aggregation, a genetic basis for Chiari I has been suggested.[7] Recent studies suggest linkage to chromosomes 9 and 15.[8] It is hypothesized that Chiari Type I originates as a disorder of para-axial mesoderm, which subsequently result in the formation of a small posterior fossa. The development of the cerebellum within this small compartment results is overcrowding of the posterior fossa, herniation of the cerebellar tonsils, and impaction of the foramen magnum.[9] Arnold–Chiari Type 1 malformation (CM1) is characterized by downward displacement of the cerebellar tonsils of >5 mm through the foramen magnum into the cervical spine.[1011] Common presenting signs/symptoms of CM1 include headache, neck pain, cranial nerve compression, brainstem compression, cerebellar malfunction, and syringomyelia. Ocular manifestations consist of palsies primarily of cranial nerves 3rd and 6th. Papilledema is a rare but known manifestation of CM1.[212] Nyctalopia is mainly caused by Vitamin A deficiency.[13] Treatment involves posterior fossa decompression ± duroplasty.[14] We report a serendipitously diagnosed case of CM1 with papilledema who presented primarily with nyctalopia and headaches.

Case Report

An 8-year-old-boy presented with a 2-month history of night blindness to our hospital. He was asymptomatic in the daylight, but almost blind in dark to the extent, where he found walking difficult. He also experienced bumping into street furniture and objects while walking through the streets after dark. There was no personal or family history of ophthalmic disease. On further questioning, he also gave a history of intermittent headaches distinctively worsening on physical exertion and Valsalva maneuvers, head dependency and posture changes, and ringing in the ears for the past 1 year. He is developmentally normal.

On examination, the boy's head circumference was 50 cm (>97th percentile). He had ataxic gait, oculomotor apraxia, and signs of cerebellar involvement. Power, cranial nerve, and sensory examinations were normal. There were no extrapyramidal movements, seizures, neurocutaneous markers, facial dysmorphism, overt signs of Vitamin A deficiency, hypertension, bowel bladder dysfunction, and hepatic or splenic enlargement.

Fundus examination was significant for Grade 2/5 optic disc edema. Visual acuity was 20/20 OU. Humphrey visual field showed superior and inferior arcuate nerve fiber layer-type defects with mean deviations of −13.50 dB OD and −14.50 dB OS, respectively.

We started the patient on Vitamin A supplementations for nyctalopia, which showed an improvement over the next 6 weeks. However, with the persistence of signs of raised intracranial pressure (ICP), hypervitaminosis/hypovitaminosis-associated pseudotumor cerebri was suspected, for which neuroimaging was done. Computed tomography of the brain showed caudal descent of cerebellar tonsils into foramen magnum (9.5 cm below Chamberlains line), causing mass effect on the cervicomedullary junction and mild dilatation of the ventricular system. Magnetic resonance imaging (MRI) of the brain and spinal cord also showed congruous findings with peg-like tonsillar morphology [Figures 1 and 2]. Bony calvarium, spinal cord, conus medullaris, and cauda equina were normal. These findings were consistent with the diagnosis of Chiari Type 1 malformation. Our patient underwent conservative medical management with carbonic anhydrase inhibitor, and he is asymptomatic for the past 6 months.

Figure 1

Cranial magnetic resonance imaging showing cerebellar tonsillar herniation through the foramen magnum (Chamberlains line)

Figure 2

Spinal magnetic resonance imaging screening is not showing any evidence of syringomyelia

Differential diagnosis

In general, normal visual acuity, minimal nerve fiber loss, and bilateral optic disc edema are the consequences of papilledema.[15] The differential diagnosis for disc edema in this patient includes intracranial space-occupying lesion causing hydrocephalus, idiopathic intracranial hypertension (IIH), cerebral venous outflow obstruction, malignant hypertension, and meningoencephalic lesions. IIH is primarily a diagnosis of exclusion delineated as having features of high ICP (papilledema, headaches, diplopia, etc.,), a normal neurologic examination, an unexceptional cerebrospinal fluid (CSF) analysis with the absence of ventricular augmentation, or intracranial space-occupying lesions on neuroimaging studies. IIH commonly affects overweight young women in their second and third decades.[1617] MRI imaging affirmed CM1 as the unparalleled cause of papilledema in this patient [Figures 1 and 2].

Discussion

Arnold–Chiari malformations were first described in 1883 by Cleland in pediatric autopsy specimens and later in 1891 by Chiari.[1819] Bestowing the name of his teacher Julius Arnold, and his name, the congenital hindbrain disorder is named Arnold–Chiari malformation.[2021]

Chiari malformation is subdivided into Types 0 through 4. Types 1 and 2 are of greater clinical importance than Types 0, 3, and 4.[1234] The CM1 malformation is characterized by downward displacement of the cerebellar tonsils (>5 mm) through the foramen magnum (Chamberlains line) into the cervical spine.[1011] It is commonly associated with cervical syringohydromyelia (syrinx) and rarely presents clinically before adolescence. Researchers have determined that the length of tonsil descent in a Chiari malformation does not always correspond to the severity of symptoms or to the response to treatment. In fact, some individuals are classified as having Chiari malformation Type 0, in which there is minimal or no descent of the cerebellar tonsils. These individuals still have symptoms associated with a Chiari malformation, most likely due to abnormalities in the flow of CSF within the skull and spinal canal.[7222324]

The most common symptom associated with a Chiari malformation is occipital headache. This headache is felt near the base of the skull and may radiate to cause pain in the neck and shoulders. They can be severe and may be described as sharp, brief, throbbing, or pulsating. Occipital headaches can be brought on or worsened by coughing, straining, sneezing, or performing Valsalva maneuver. Ocular abnormalities include diplopia, photophobia, blurred vision, nystagmus, and retro-orbital pain. Vertigo, dizziness, tinnitus, and bilateral hearing impairment can also develop. Other impairments include cranial nerve compression, brainstem compression, cerebellar malfunction, swallowing difficulty, scoliosis, motor weakness, impaired oropharyngeal function, bowel bladder disturbances, and developmental delay. Cases of sudden death have also been reported. Cranial 3rd and 6th nerve palsies are common. Papilledema is a rare manifestation of CM1 malformation.[912]

One noticeable facet of our case was the gender, the age of presentation, nyctalopia, and the absence of syringomyelia [Figure 2]. Although quondam articles on papilledema in CM1 have primarily recorded patients in their second–third decades (the classical age at which Chiari I expounds clinically), older patients have been documented.

Papilledema is usually associated with IIH (pseudotumor cerebri) and hypervitaminosis A. Whereas the same caused by Vitamin A deficiency is a rarity.[25]

Evaluation of nyctalopia led us to the examination of the optic fundus, which fortuitously showed Grade 2/5 papilledema. As a protocol for finding the cause and persistence of papilledema, neuroimaging was done which revealed the features of CM1 [Figures 1 and 2]. To the best of our knowledge, this case of papilledema and nyctalopia associated with Chiari I malformation in an 8-year-old boy is a rarity.[262728]

Papilledema in conjunction with the CM1 has been described as being predominantly due to obstructive CSF flow. Depending on the degree or site of the compression, patients may manifest papilledema with or without further neurological abnormalities. When cerebellar tonsillar ectopia is identified, careful radiographic and clinical consideration of IIH is warranted to avoid misdiagnosis as CM1 alone.[29] CSF flow analysis through foramen magnum with phase-contrast cine MRI helps distinguish symptomatic Chiari I from asymptomatic cerebellar ectopia/IIH and helps predict response to surgical decompression.[3031] This was not done in our patient as he was symptomatic.

Treatment

Asymptomatic patients without syringomyelia whose CM1 has been discovered incidentally on MRI do not require surgery. In this group, if the radiographic abnormality appears significant, the patient should be educated about the disorder and advised to seek medical care if symptoms develop in the future. Although posterior fossa decompression with/without duroplasty being the treatment of choice for symptomatic CM1, prognosis for such cases with papilledema following surgery is poorly documented. With this procedure, a surgeon creates room by removing small pieces of bone in the back of the skull, thereby enlarging the foramen magnum. This decompresses the brainstem, and may allow the cerebellar tonsils to move back to a more normal position. While the complete resolution of symptoms following surgery in all four of their patients was noted by Vaphiades et al., our patient's visual symptoms improved, but he was left with a residual field defect and bilateral optic nerve atrophy.[2732] Nyctalopia was treated with Vitamin A supplements. Our patient responded well to the supplementation. The child was consulted with a neurosurgeon and advised conservative medical (acetazolamide therapy) management and surgery if symptoms increased. At present, the boy is asymptomatic.

Conclusions

We present an unusual and serendipitous case of CM1 presenting as nyctalopia and headache. Further evaluation of the case revealed papilledema and CM1 on neuroimaging.

Fundoscopy in a case of nyctalopia represents a reproducible, noninvasive, investigation that can detect papilledema in CM1 malformation. Fundoscopy as a tool can be used in combination with other parameters and neuroimaging. This technique may further be important for the follow-up of postsurgical patients in monitoring optic disc edema in a long-term follow-up.

Differentiating Chiari I with papilledema from IIH due to analogies in presentations can be difficult. MRI imaging of the sagittal craniocervical junction should be done in all patients with IIH. CSF flow analysis through foramen magnum with phase-contrast cine MRI helps distinguish symptomatic Chiari I from asymptomatic cerebellar ectopia and helps predict response to surgical decompression.

Surgical decompression of the posterior fossa is the only treatment shown to be persistently effective in Chiari I patients with papilledema.

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Conflicts of interest

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