PRENATAL DIAGNOSIS, VOL. 12,653-659 ( 1 992)

PRENATAL DEMONSTRATION OF A CERVICAL MYELOCYSTOCELE

RAW BHARGAVA*, D. IAN HAMMOND*'t, RONALD J. BENZIET,

Faculiy of Medicine, University of Oiiawa, Oriawa, Canada and *Department of Diagnostic Radiology and TDepartment of Obsieirics and Gynecology, Ottawa General Hospital, 501 Smyih Road, Oiiawa,

Canada, KI H 8M: $Department of Neurosurgery and4Deparimeni of Diagnostic Radiology. Children? Hospital of Easiern Oniario. 401 Smyth Road, Ottawa, Canada, KIHSLI

E. CARLOS G. VENTUREYRAJ, MICHAEL J. HIGGINSJ AND DAVID J. MARTIN§

SUMMARY Myelocystocele is a rare spinal cord disorder and has not been described prenatally. We report a case in which prenatal ultrasound and magnetic resonance imaging (MRI) demon- strated a posterior cervical mass which was initially thought to be a rneningocele or an atypical cystic hygroma. Surgery performed at 1 day of age showed this to be a myelocysto- cele. Therefore, the differential diagnosis of an extracranial cystic mass in the posterior cervical region should be expanded to include myelocystoceles.

KEY WORDS Myelocystocele Ultrasound Magnetic resonance imaging Spinal cord, abnormalities Prenatal diagnosis

INTRODUCTION

High resolution ultrasonography and genetic amniocentesis have proven to be reliable techniques for the characterization of posterior neck masses in the fetus. The principal conditions in differential diagnosis are cystic hygroma, cervical meningocele, and cervical myelomeningocele, and rarely neoplasms such as teratoma, neuroblastoma, and haemangioma (Romero et al., 1988). We report what we believe to be the first case of a cervical myelocystocele seen in utero with ultrasound and MRI. The definitive diagnosis was made a t surgery on day 1 of extrauterine life. At 6 months of age, the child has no demonstrable neurological deficit .

CASE REPORT

A 35-year-old Caucasian woman underwent routine ultrasound examinations at 8 and 20 weeks' gestation, each examination revealing a normal fetus. There was no family history of congenital anomalies or exposure to known teratogens. Repeat ultrasonography at 24 weeks' gestation showed an ovoid, thin-walled cyst measur- ing 3.7 cm in greatest diameter, situated in the posterior cervical region. This led to referral at 26 weeks to our high-risk pregnancy unit, where we corroborated these findings (Figure 1). There was no evidence of a spinal defect or of any associated anomalies of the brain or skull. The remainder of the fetus appeared normal. A

Addressee for correspondence: Dr Ian Hammond, Department of Radiology, Ottawa General Hospital, 501 Smyth Road, Ottawa, Ontario, Canada, KIH 8L6.

01 97-385 1/92/080653-07$08.50 0 1992 by John Wiley & Sons, Ltd.

Received October 1991 Revised 26 November 1991

Accepted I2 December 1991

654 R. BHARGAVA ET AL.

Figure I . Axial scan through the lower occipital region angled caudally showing a cystic mass contacting the skull. Markers spaced at I cm intervals

genetic amniocentesis revealed normal levels of alpha-fetoprotein and acetyl- cholinesterase. and 46,XY karyotype. In ufero MRI was performed in an attempt to assist in diagnosis. This confirmed the presence of the cystic mass but gave no added diagnostic clues (Figure 2). Serial sonograms during pregnancy showed enlarge- ment of the mass, which developed a cyst-within-a-cyst appearance (Figure 3). We could not identify spinal cord elements within the lesion or any communication with the neural tube.

A 2480 g male infant was born at 38 weeks' gestation in March 199 1 by Caesarean section and was neurologically intact with Apgar scores of 5 at 1 min and 9 at 5 min. Physical examination was normal except for a 4 x 4 cm flaccid mass in the posterior cervical region at C6-7 covered with thin skin and containing tufts of hair at its base. Ultrasonography of the newborn's head, abdomen, and pelvis were normal. Ultrasound examination of the neck confirmed the prenatal findings.

At 1 day of age, the child underwent surgery, which demonstrated a cystic mass filled with sero-sanguinous Nuid, with numerous adhesions around its dome (Figure 4). The mass was gradually dissected down to a narrow neck and was amputated. The residual neck, which contained a central lumen, entered a small spina bifida defect in the vertebral laminae measuring less than 1 cm in diameter, and was con- tinuous with the central canal of the spinal cord. This neck, or neural stump, tethered the cord posteriorly. After successful microsurgical release of the cord, the defective dura and overlying soft tissues were closed and the redundant skin trimmed and closed without tension.

PRENATAL DEMONSTRATION OF A CERVICAL MYELOCYSTOCELE 655

Figure 2. Sagittal iri urero M R I scan showing the relationship between the mass (arrows) and the fetal cranium and spine

Pathological examination of the cyst revealed a dilated irregular lumen lined by ependynial tissue and surrounded by disorganized neural tissue composed of glial cells, neurons, and neuropil. This neural mass was then surrounded by vascular connective tissue and covered by atrophic dermis and epidermis.

Post-operative radiographs of the spine showed a congenital scoliosis convex right in the mid-thoracic spine due to a hernivertebra at T6.

The child has shown normal development on his recent follow-up at 6 months of age. Periodic monitoring of the neurologic and orthopaedic function are planned until spinal growth is complete in the late teens.

DISCUSSION

A myelocystocele is a localized dilatation of the central canal of the spinal cord (hydromyelia) which produces a fluid-filled sac or diverticulum protruding through the cord and the defective dorsal dura between the posterior elements of the vertebra (Lassman et al., 1968; McLone and Naidich, 1985). This sac is lined by ependyma and is covered by meninges (meningocele) and skin. The most common location is at the caudal end of the neural tube, where the lesion is called a terminal myelocystocele. Occasionally, myelocystoceles arise from the anterior aspect of the spine.

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Figure 3 . Similar view at 33 weeks’ gestational age showing two distinct cystic components, the inner one of which represents the hydromyelic sac

Myelocystoceles are rare, sporadic lesions with no known familial recurrence. Lemire and Beckwith (1982) found 11 cases among 317 skin-covered lumbosacral masses, given a frequency of 3.5 per cent similar to the frequency of 4 per cent noted by McLone and Naidich ( 1 985). Terminal myelocystoceles often accompany mid- line abdominal and pelvic anomalies as part of the OEIS complex, which consists of omphalocele, exstrophy of the bladder, imperforate anus, and spinal anomalies (Peacock and Murovic, 1989). The significance of an apparent excess of affected white males, as in o u r case, is unknown.

Myelocystoceles in the lumbar region have been experimentally induced in Syrian hamsters exposed to retinoic acid at the time of neural tube closure (Tibbles and Wiley, 1988), but induction of cervical myelocystoceles has not been reported.

The most common presentation of a myelocystocele is that of a subcutaneous mass. The expansion of the central canal does not usually produce the signs of cord disrup- tion seen in syringomyelia and this suggests that its embryologic origin predates most of the cellular development of the spinal cord. Unlike the situation with rnyelo- meningocele, where the nerves traverse the cavity and are subject to entrapment and damage, the spinal nerves simply pass around the hydromyelic swelling of the myelo- cystocele. Thus, neurological signs and symptoms may be initially minimal or absent. Lumbar myelocystoceles have no known association with the Chiari malformation.

There have been few reports of myelocystoceles of the cervicothoracic region (Friede, 1990; Steinbock and Cochrane, 1991). These lesions are thought to be identical to the syringocele and syringomyelocele which other authors have described

PRENATAL DEMONSTRATION OF A CERVICAL MYELOCYSTOCELE 657

Figure 4. Surgical impression of the lesion. 1 =Skin; 2=dura and arachnoid; 3 =meningocele cavity; 4 = hydromyelic sac; 5 =defective posterior neural arch; 6 = spinal cord

(Steinbok and Cochrane, 1991). As in other sites, the initial sign is usually a swelling over the spine, which may gradually increase in size. Dorsal skin anomalies typical of occult spinal dysraphism may be present. Plain spinal radiographs may show spina bifida and anomalies such as hypoplastic laminae and hemivertebrae, but specific pre-operative diagnosis will require sonography, computerized axial tomography, myelography, or MRI, alone or in combination. M R I is now thought to be the best tool for postnatal diagnosis (Peacock and Murovic, 1989) but, unfortunately, time constraints prevented us from obtaining a pre-operative MRI scan. In cervical myelocystoceles, the narrow connection between the subcutaneous cystic portion of the lesion and the central canal of the spinal cord may become obstructed and impossible to visualize. Even so, the lesion may expand slowly because of the ectopic production of cerebrospinal fluid, as in the case reported by Suneson and Kalimo (1 979), where the myelocystocele contained structures resembling choroid plexus.

Anatomically, the cervical myelocystocele has three major components: the hydromyelic sac, the covering meningocele, and the spina bifida through which the lesion protrudes. The hydromyelic component has an ependymal lining which is

658 R. BHARGAVA ET AL.

usually surrounded by attenuated neural and glial elements. The meningocele is lined by arachnoid and is continuous with the subarachnoid space. The lesion may be in turn covered exteriorly with fibrolipomatous subcutaneous tissue and with skin. In our patient, the zone of spina bifida was small and was confined to the non- ossified region of the vertebra; for these reasons it could not be seen prenatally. The cyst-within-a-cyst appearance, which is also seen with some occipital cephaloceles (Goldstein et al., 1991) correlates well with the morbid anatomy, the inner cyst most likely representing the hydromyelic sac, and the outer cyst the dura and skin.

The prognosis for patients with cervical myelocystoceles seems to depend on associated cranial abnormalities. In earlier case reports, the lesions were isolated defects and the patients had no neurological deficits. However, all three of the patients reported by Steinbok and Cochrane (1991) had an associated Chiari I1 malformation and hydrocephalus. Two of these children have been followed for more than 1 year and have significant spinal cord dysfunction. Genetic counselling for future pregnancies may be given with some reassurance because there have been no reports of intrafamilial recurrences.

CONCLUSION

Cervical myelocystocele, although rare, should be added to the traditional differ- ential diagnosis when a cystic lesion of the posterior neck is demonstrated on prenatal ultrasound. A normal amniotic fluid alpha-fetoprotein reduces the likeli- hood of an open neural tube defect, but it is unlikely that a closed, simple meningocele with a small spinal defect would be distinguishable from a myelocysto- cele sonographically. The other common neck mass, cystic hygroma, is usully sep- tate, extends laterally, and is often associated with fetal hydrops and chromosomal abnormalities.

Although intrafamilial recurrences of myelocystoceles have not been reported, it would seem prudent to monitor subsequent pregnancies with amniotic fluid alpha-feto protein determination and ultrasonography.

ACKNOWLEDGEMENTS

We thank Dr Alasdair Hunter, Chief of the Department of Genetics at the Children’s Hospital of Eastern Ontario for providing us with much valuable information on myelocystoceles. We also thank Kathy Sadler and Margaret Crosbie for secretarial assistance.

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