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«OPHTHALMOLOGIC COMPLICATIONS OF MENINGOMYELOCELE: A LONGITUDINAL STUDY* BY Albert W Biglan, MD INTRODUCTION MENINGOMYELOCELE OR SPINA BIFIDA IS A ...»

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OPHTHALMOLOGIC COMPLICATIONS OF

MENINGOMYELOCELE: A LONGITUDINAL

STUDY*

BY Albert W Biglan, MD

INTRODUCTION

MENINGOMYELOCELE OR SPINA BIFIDA IS A DEFECT IN DEVELOPMENT

that is manifest as a failure of the vertebral arches of the spine to fuse

completely. This results in dysplastic growth of the spinal cord and its meningeal coverings. The defect is caused by a primary failure of the neural tube to close.1-6 Considerable knowledge has accumulated over the past three decades regarding neural tube development. It is now clear that the lower lumbar myelomeningocele results from defective closure of the posterior portion of the lower neural tube during the fourth week of gestation.

During normal development, the central nervous system develops from neuroectoderm on the dorsal aspect of the embryo. A groove devel- ops in the neuroectoderm with upward growth of lateral ridges that later fuse to form a tube from which the spinal cord and brain develop. In normal development, this tube is covered by primordial tissue that will form skin, muscle, bone, and the meninges. If there is defective closure, or the closure is incomplete, the spinal cord may be dysplastic and may be exposed to the external environment.5,6

TERMINOLOGY

The clinical expression of the defect is variable in its degree of severity and its location. The defect may be slight or clinically insignificant. Spina bifida occulta refers to a minor defect in closure of bones of the vertebral arches and is usually detected on routine spine x-rays.3-6 The term meningocele is used to describe a more extensive defect that includes vertebral arch defects and dorsal herniation of the meninges, but no alterations in the spinal cord. In this condition, the function of the distal spinal cord is usually normal.

*From the Department of Ophthalmology, the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.

TR. AM. OPHTH. Soc. vol. LXXXVIII, 1990 390 Biglan The term myelomeningocele or meningomyelocele is used to describe an extensive defect that includes spina bifida and protrusion of the men- inges and spinal cord through the defect. The affected segment of spinal cord is usually dysplastic, and may lack the protective integument that normally covers and protects the spinal cord. When this occurs, cere- brospinal fluid can leak around the defect and the spinal cord is exposed and susceptible to infection.

The term spina bifida describes the condition in which two correspond- ing laminae, arising from the vertebral processes, fail to unite at the midline. The term is more commonly used to describe any defect in the formation of the spinal column or its meningeal covering. The most common location for neural tube defects is in the lumbar region of the spine: 80% of the defects are in this location.6 More rostral defects involve the upper thoracic and cervical spinal cord. Less frequently, an encephalocele will form when the defect involves the upper cervical spine or the occipital area of the skull. In this instance, brain tissue may occupy the sac.

Defects in the lower spine may involve the lumbar and sacral nerves.

When a myelomeningocele involves the lumbar nerves, it is usually associated with hydrocephalus. This is due to the frequent co-occurrence of the Arnold-Chiari malformation in which the upper spinal cord, medulla, and cerebellum are displaced downward and occupy the distended upper spinal cord cavity. 7-12 This defect is associated with distortion or compression of the aqueduct of Sylvius and its surrounding midbrain structures. 3,8,9, 11 PREVALENCE Spina bifida or meningomyelocele is one of the most common birth defects. It occurs with a frequency of 0.4 to 1 per 1,000 live births in the United States, and with a higher incidence in white infants than in black infants. 6,13 Eckstein and Macnabl reported an incidence of three children with spina bifida per 1,000 live births in the United Kingdom. Because many reporters group children with spina bifida with those who have congenital hydrocephalus, the reported incidence of hydrocephalus must be taken into account when investigating the prevalence of spina bifida.

Hydrocephalus occurs with a frequency of 1 in 400 live births in Great Britain and in 2 per 1,000 live births in Japan.'4 To assist in the interpretation of these reports, the reader should be aware that approximately 80% of patients in these reports have spina bifida or myelomeningocele.3,6 Meningomyelocoele 391 CAUSES The cause of spina bifida is unclear. Polygenic inheritance has been reported to play a role, but there is also evidence that environmental factors influence the incidence of this condition: in the United Kingdom and Ireland the incidence of spina bifida increased during periods of malnutrition.6 In this particular case, an association was drawn between spina bifida and the consumption of blighted potatoes although, with better understanding of maternal nutrition during gestation, the "bad potato" theory has been discredited. 15,16 It was found that when nutrition in this population was corrected, the occurrence of spina bifida declined.

PREVENTION It is clear the poor maternal nutrition is associated with fetal neural tube defects. Animal studies suggest that folic acid is one of the nutrients necessary for normal closure of the neural tube. A double-masked, randomized study of folic acid versus placebo administration during pregnancy demonstrated a significantly lower incidence of neural tube defects in mothers who took folic acid than in those who took placebo. 17 Milunsky and co-workers17 showed that folic acid supplementation given early in pregnancy in addition to multivitamin supplementation results in a prevalence of neural tube defects of 0.9 per 1,000 versus 3.5 per 1,000 for those who used multivitamins alone. If multivitamins without folic acid were used, or multivitamins and folate were started after the seventh week of pregnancy, the prevalence of defects was similar to that in the untreated group.





DETECTION Defects in closure of the neural tube can be detected prenatally because they are associated with an increased level of maternal serum alpha fetoprotein.'1819 About 75% of fetuses with an open myelomeningocele can be detected at 14 to 20 weeks gestation, when the parents may be given the option of terminating the pregnancy. 13 TREATMENT Myelomeningocele has been recognized for several centuries; however, effective treatment and prolongation of survival have only been achieved during the last 30 years.

Tulp?0 in 1641 introduced the term "spina bifida" to describe a congenital malformation that was associated with a cystic protrusion from the vertebral column. Children who had this defect died shortly after birth.

Two centuries later, Morgagni7 recognized the important association of Biglan 392 spina bifida and hydrocephalus. Surgeons in the 18th and 19th centuries were technically able to close the spinal defect but the functional results and survival were poor. Early in the 20th century operations to close the defects were performed soon after birth, but infection around the closure site and meningitis usually caused death in the perinatal period. 1,21-24 The advent of sulfonamide antibiotics brought a decline in deaths from spina bifida due to infection and meningitis but the children who survived developed debilitating hydrocephalus with massive enlargement of their heads.

Hydrocephalus occurs in 90% of the children affected with myelomeningocele.12 Hydrocephalus may not be present at birth, and the clinical signs of this condition may not develop until 2 to 3 weeks following closure of the defect.25 Currently most cases of hydrocephalus are recognized and treated within the first month of life.

The cause of hydrocephalus is related to the Arnold-Chiari malformation: caudal displacement of the fourth ventricle with compression and thinning of the upper medulla and lower pons due to downward displacement of the medulla and the cerebellum through the foramen magnum into the upper cervical spinal cavity.8'12'25,26 This defect permits cerebrospinal fluid (CSF) to exit the caudally displaced fourth ventricle but prevents its ascension into the cerebral cavity to be absorbed because the CSF flow is impeded by the herniated tonsils of the cerebellum.

To treat hydrocephalus, a shunt is placed surgically to relieve the pressure of excess CSF Shunting can prolong survival, although early attempts to control hydrocephalus were not very successful because of technical problems. In a series of patients treated before 1962, the mortality was 35%.1 Shunting of CSF was initially accomplished with a diversion of the fluid from the spinal cavity into a ureter, necessitating a nephrectomy. Later, ventriculoatrial or ventriculoperitoneal shunts were used that regulated CSF flow and thus fluid pressure by pressure-sensitive valves. It was two of these valves-the Spitz-Holter and the PudenzHeyer valves-that permitted accurate control of intracranial pressure and successful treatment of hydrocephalus. This treatment did not meet with universal approval at first, and there as lack of agreement on which children should be treated.27-30 However, after several reports appeared of children being treated successfully and surviving, this technique became widely accepted.31-33 SURVIVAL In 1966 Eckstein and Macnab' reported on the impact that modern treatment of hydrocephalus and myelomeningocele had had on survival.

Meningomyelocoele 393 They found that in the United Kingdom mortality from these conditions decreased from 60% to as low as 20% between 1959 and 1963 and that most of the patients whose intracranial pressure was normalized had normal intelligence.

In 1967 Sharrard et a131 reported on a landmark clinical study of 40 children who were randomly assigned to surgical or nonsurgical treatment. After a 4-year follow-up, it was clear that early closure of the myelomeningocele improved the patient's function and survival. The results from other studies supported these findings.21 Survival rates improved from 15% without treatment to 60% with prompt surgery.28 In 1972, only 50 of each 100 patients with hydrocephalus were expected to survive.4 In a more recent report of 200 unselected patients who were treated aggressively and followed for 5 to 9 years, the mortality was only 14%. Of the survivors, 73% had intelligence quotients of 85 or better, 75% were ambulatory, and 87% were continent of urine.4 From a posture 20 years ago of neglect for patients with severe hydrocephalus, physicians have developed the current strategy of multidisciplinary team assessment and aggressive treatment. Neurosurgeons, urologists, orthopedic surgeons, psychologists, teachers, and in some centers ophthalmologists now participate in various stages of treatment, which starts with closure of the defect, usually with a microsurgical technique, within the first 3 days of life.34 Early closure of the defect has decreased the number of patients who have meningitis, and is also believed by some to promote maximal function of the dysplastic spinal cord and the structures it innervates.

SYSTEMIC COMPLICATIONS

As children with spina bifida survive into adulthood, new management problems have emerged. Thus habilitation of children has become the final frontier."121'35'36 As children born with spina bifida reach their school years, teens, and early twenties, problems that arise include pressure

-ulcers of the skin, orthopedic deformities, urologic defects, educational, sexual, and social adjustment problems-and ophtialmologic problems.30'37'38 The orthopedic problems such children experience are related to loss of sensory and motor function. Approximately 90% of affected children have a defect in the lumbar region and this results in muscle weakness, muscle atrophy, and loss of sensory function of the lower extremities. Upper lumbar spine involvement (Ll-2) usually means confinement to a wheelchair. Lower-level (L3-5) lumbar involvement usually is consistent with ambulation with braces or crutches. Other orthopedic comnlivations include: contracture of joints, hyperextension deformities, frequent fractures, kyphoscoliosis, and hip dislocations.37 Biglan 394 If the sacral nerves are involved, individuals with spina bifida have some degree of neurogenic bladder. Complications of resultant urinary incontinence, even when managed by frequent catheterizations, include urinary tract infections, hydronephrosis, and renal calculi.37

OPHTHALMOLOGIC COMPLICATIONS

It is important to realize that the individuals with spina bifida we currently examine are the "products" of successful medical and surgical management. In earlier years, they would have died before orthopedic or urinary bladder problems needed to be addressed. With long-term survival of those with spina bifida has come yet another problem-ophthalmic complications. The importance of the involvement of the ophthalmologist in the care of children with spina bifida has only recently become evident. To my knowledge, there are no reports earlier than 1960 of visual problems in children with myelomeningocele, probably because children died before ophthalmologic problems rose high enough on the list of concerns to be addressed.

In 1965 Goddard38 suggested that ophthalmologists should become involved in the care of children with spina bifida "to attend to the defects of vision, optic atrophy, corneal ulceration, and strabismus."

The early literature on ophthalmic care of children with spina bifida was confusing as patients with spina bifida were grouped with children with hydrocephalus. In this same report, Goddard38 studied a group of 251 patients with hydrocephalus, most of whom had spina bifida. She found that optic atrophy was present and postulated that it was caused by "stretching of the optic nerves" and by pressure exerted on the optic nerves that resulted in compromise of the blood supply to the nerves.



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