INTRODUCTION

Neurenteric cyst of the spinal canal is a rare developmental disorder of endodermal origin. (9) It usually occurs at the cervico-thoracic junction or in the region of the conus medullaris. (7) Its origin is similar to the posterior medlastinal or abdominal cyst which often co-exists. (6) The cyst may lie anterior or posterior to the spinal cord intradurally or it may lie in an intramedullary location. (11) Isolated intradural extramedullary cyst is extremely rare. It is often adherent to the spinal cord, to the dura or both. The prognosis is excellent in these patients. Hence, once the lesion is recognized, every effort should be made to remove it. An associated vertebral cleft is usually present in the vertebra.

CASE REPORT

Case 1. A 25 years old man was admitted in January 1997 with a one month history of pain in the neck and bilateral brachalgia, heaviness of the lower limbs and difficulty in walking. There was no disturbance of his bladder or bowel functions. His past medical history was remarkable in that he had undergone a cervical operation in Syria four years earlier when a C7 and T1 laminectomy was made for similar symptoms. Examination revealed a flaccid type of weakness distally in both upper limbs with reduction of tendon jerks. There was a spastic paraperesis power-MRC (Grade 4 on the right) and (Grade 3 on the left) with brisk tendon jerks, upgoing plantars and sustained ankle clonus bilaterally. Pain and temperature sensations were reduced with a level at T1 dermatome. Vibration and joint position senses were normal. There was left sided miosis, ptosis and enophthalmos. Systemic examination showed no abnormality.

Routine laboratory studies were normal. X-rays of the cervical spine showed evidence of C, and 1I', laminectomy. Magnetic Resonance Imaging (MRI) showed a lesion located at the cervicothoracic junction which was hypointense on T1 and hyperintense on T2 weighted images. Axial T1-weighted image (Fig. 1) showed a multilocular cyst located anterior to the cord which was compressed and reduced to a thin shell. The cyst bulged laterally more on the left side. Sagittal T2 weighted MR image (Fig. 2) showed the lesion extending from C7 to T1 levels. Xray of the chest was normal. The ultrasound of the abdomen revealed no abnormality.

At operation, the cervico-thoracic spinal canal was explored by extending the laminectomy up to T2. The dura was opened. A pale cyst measuring 3 x 2 cm was found anterior to a thinned out cord. It was adherent to the dura with fibrous septae. Using microscope the dural adhesions were released.

The cyst was mobilised from the cord and aspirated. The aspirate was clear. The wall of the cyst was then excised.

The dura anterior to the cord and the vertebral bodies were intact. Histologically (Fig. 3) it was a multilocular cyst lined by columnar mucus secreting epithelium. Postoperatively, the weakness in left lower limb increased (power MRC Grade 2 proximally and Grade 1 distally). This weakness improved during the next three weeks to Grade 4 proximally and Grade 3 distally. He was able to walk. His pain and temperature sensations returned to normal. The tendon jerks were still brisk but there was no ankle clonus. He was then referred for active rehabilitation.

Figure 1 — Axial T1-weighted magnetic resonance imaging (MRI) showing a multilocular cyst anterior to a thinned out cord and its lateral bulging more on the left side.

Figure 2 — Sagittal T2-weighted MRI showing the superoinferior extent of the lesion .

	Figure 3 — Photomicrograph (H and E x 100) showing a cyst lined by columnar mucus secreting epithelium .

Follow-up at 18 months revealed minimal residual weakness in the left lower limb only distally.

Case 2. A 16 years old boy was admitted in May 1993, with a 4 month history of unremitting low backache and right sided anterior thigh pain. There was no disturbance of his bladder or bowel functions. His past medical history was unremarkable. Examination revealed a healthy boy with weakness and wasting of his quadriceps bilaterally. There was dulling of pinprick sensation over the distribution of L3 to S1 dermatomes on both sides. The knee jerks were absent and the ankle jerks depressed. Vibration and joint position as well as the straight leg raising bilaterally were restricted. There was no tenderness over the spine. Systemic examination showed no abnormality. Routine laboratory studies were normal. X-rays of the lumbar spine showed no abnormality. Myelogram demonstrated a complete intradural block at L2-3 level. Postmyelogram CT showed a low density mass with clear margin.

At operation, Ll and L2laminectomy was done. When the dura was opened, a cystic mass measuring 2.5cm x 1.5cm was found within the cauda equina and adherent to the tip of the conus medullaris. It had extended downwards to the lower border of L2 vertebra displacing the nerve roots. Using microscope the cyst was mobilised and aspirated. The aspirate was viscous. The wall of the cyst was then excised. The dura anterior to the cauda and the vertebral bodies were intact. Histologically, it was a unilocular cyst and lined by similar type of columnar mucus secreting epithelium, as described in patient.(1)

The postoperative course was uneventful. Follow up after 5 years showed that the patient was asymptomatic, well and with normal neurology of the lower limbs.

DISCUSSION

Neurenteric cysts probably arise early in embryogenesis when the endoderm and ectoderm are close together. During the third week of gestation the embryo is in its trophoblastic stage, when a communication exists between the yolk sac (destined to become the gut) and the dorsal surface of the embryo (the amniotic sac). This is neurenteric canal and it connects transiently the future enteric cavity with the neural groove in the region of the coccyx. This connection disappears within 2 to 3 days. Reconstitution of enteric cavity then follows. Accessory neurenteric canals may occur proximal to the coccygeal tip. These may persist and may give rise to neurenteric cysts.(4) The location of the cyst depends upon the site of persistence of the accessory canal. The site of predilection is the cervico-thoracic junction and the conus medullaris (7) as was in our patients. According to Bently and Smith, (3) neurenteric cysts are invariably associated with a vertebral cleft. But there are a few reports of intraspinal neurenteric cyst not associated with any abnormality of the spine. (8,12,14,15) Our patients did not have any abnormality of the spine (vertebral cleft) indicating a complete sequestration of the endodermal element in the spinal canal.

Neurenteric cyst behaves as a space occupying lesion, causing compression of the nervous tissue. The clinical picture therefore depends on its location. Neurological features, in order of frequency, are pain, weakness, sensory loss and sphincter disturbances.(5) Additionally, burning dysesthesias may occur. This may be aggravated by coughing, sneezing and recumbency. (6,12,16) The symptomatology is progressive in 75% of patients and intermittent in the rest. (1) It was progressive in both our patients. There are no characteristic clinical findings or history associated with this disease. The myelogram merely suggests an intradural space occupying lesion. The MRI clearly defines the cyst.(2,10,14)

It was not possible to diagnose the nature of the lesion pre-operatively. The presence of septae in the cyst was against the diagnosis of an arachnoid cyst. Diagnosis is usually made histologically, as was in our patients. Wilkins and Odom (17) have grouped the intraspinal neurenteric cysts into three groups- Group A, consisting of cysts with simple epithelial lining over a basement membrane; Group B, having epithelial folds, invaginations and other elements of gastrointestinal tract, muscle and cartilage; and Group C, showing presence of ependymal and glial tissue in addition to those of Group A and B. Our patients appear to be in Group A.

Surgery is the treatment of choice for neurenteric cyst. Untreated lesion continues to grow. Delay in treatment may lead to progressively increased neural compression and irreversible changes. At times the cyst may rupture and may cause dense dural adhesions, as was the case in our patient. 1 Prognosis is excellent in these patients when diagnosed early and removed surgically as was in our patients. Late diagnosis and partial excision are associated with poor prognosis.

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