Introduction

Arachnoid cysts (ACs) of the spinal canal are rare, histologically benign space-occupying lesions. They are predominantly located posterior to the spinal cord; the thoracic spine is the most common site.1'12 Some spinal ACs located anterior to the spinal cord have also been reported.6,8,9,12-16 ACs of the craniocervical junction (CCJ), however, are even rarer, and only six cases have been reported in the literature; all of them had shown extension to the posterior fossa.5,17-21

In the cases of spinal ACs, clinical presentation depends on the location of the lesion. Usually, they become symptomatic by causing myelopathy or radiculopathy.1-4,6-8,11,13,16-22-25 All of these symptoms typically develop over a period of months or years.1,2,6,10-12,14,19,25,26

In this report, a new case of AC with a distinct clinical course is presented and the pertinent literature is reviewed.

CASE Report

This 21-year-old man was admitted to the emergency room with a craniospinal trauma in a traffic accident. He had suffered loss of consciousness for a few minutes. On admission, he was conscious and he was complaining of headache. On physical examination, a frontal scalp laceration was noted. His neurological examination were normal. Routine laboratory examination data were within normal limits. Cervical spine X-ray films were unremarkable for fracture or dislocation. Cranial computed tomography (CT) performed on admission demonstrated that the third and lateral ventricles were mild to moderately dilated but the fourth ventricle was typically normal in size (Fig. 1). The patient was transferred to our clinic for further observation and evaluation. Then, the CT scan was repeated, because he began to experience gradually increasing headache. The scan demonstrated marked dilatation of the lateral ventricle in addition to an enlarged fourth ventricle (Fig. 2). A cystic lesion was also determined at the CCJ, which was absent in the previous CT scans (Fig. 3). Magnetic resonance imaging (MRI) revealed a well-demarcated, extra-axial cystic mass, on both Tl- and T2weighted images consistent with the same signal intensity as cerebrospinal fluid (CSF). It had displaced the spinal cord ventrally at the levels of Cl and C2 (Fig. 4). The MRI also revealed that the enlargement of the fourth ventricle was not related with the mass inside. In the following hours, his headache became worse and he began to vomit. He was transferred to the operating room immediately.

Operation

The patient underwent surgery in the prone position. Initially, an external ventricular drainage to the lateral ventricle was made, but free flow of CSF was not allowed to prevent the risk of upward herniation of vermis. A midline suboccipital craniectomy with C1-2 laminectomies were performed. Following incision of the dura, a translucent thin-walled cyst was found, which had occupied the entire dorsal half of the spinal canal at the C1-2 level. The cyst fluid was aspirated. It was clear and colorless, resembling normal CSF. After aspiration, the cyst did not re-expand and there was no CSF leakage. Using microsurgical techniques, we removed as much of the cyst wall as possible, but no attempt was made to resect the anterior wall because of its adherence to the cord. When the superior wall of the cyst occluding the foramen of Magendie was removed, free flow of CSF was observed.

Postoperative Course

The patient made a good postoperative recovery. The results of CSF examination were normal. The culture was also negative. A light microscopic examination of the biopsy specimen showed histologically the arachnoid membrane. There were no inflammatory reaction and blood pigments in the cyst wall. The CT scan obtained 7 days after surgery revealed remarkable reduction in the size of the fourth ventricle (Fig. 5).

Discussion

Based on a review of the literature, ACs of the spinal canal may be classified as either extradural or intradural.1-4,8-10,12-14,25-27 There is no gender preponderance and the diagnosis is usually established in the third through the fifth decades.1-4,6,7,10,12,22-26 However, the classification of these cysts in the literature is distinct and confusing. For the sake of simplicity, and to avoid further confusion in the nomenclature, Nabors et al.6 have classified these lesions into three major categories (Table I). The patient reported in this study presented with a type III cyst (intradural AC).

Etiology

The precise etiology of these lesions is poorly understood and remains controversial. In general, they are regarded as histologically benign developmental abnormalities of the arachnoid membrane,2-4,6-9,13,15,22-24,26,28 but traumatic and inflammatory etiologies have also been proposed.1,3,4,7,8,10-14,22,25,28 Moreover, some spinal ACs have been reported to occur in regions of previous surgery.1,15

Although we described an intradural spinal AC after mild trauma, which was proven radiographically and surgically, we can speculate upon the exact pathogenesis of the lesion. In traumatic cases, some authors have considered that intraspinal ACs arise from an area of low resistance in the arachnoid which may be dilated by the continuous CSF pulsations.3,7,8,10,14,23 In the literature, it is demonstrated that even in minor trauma, arachnoid membranes are easily thorn,29 and the friability of the arachnoid as a factor facilitating tearing is also stressed.11 In our case, we speculate that a sudden, transient elevation of CSF pressure, which occurred at the time of trauma, caused a tear of the arachnoid membrane at a location where the arachnoid was weak. Once the blind pocket formed, it increased in size due to the pulsatile behavior of the CSF pressure. Before the onset of symptoms, partial communication was sufficient to allow CSF flow at subcritical rates. But, progressive enlargement of the cyst resulted in a complete obstruction of the CSF pathways at the level of the foramen magnum, leading to symptomatic intracranial hypertension.

According to another possible etiology, there may have been a little congenital AC, and the trauma may have led to expansion of this latent cyst by the same mechanism mentioned above.

Natural History and Symptomatology

The natural history of spinal ACs is not well-understood. Although many of these cysts are encountered incidentally during imaging studies,2,3,8,9,11,13,22,26,28 they may become symptomatic as they progressively expand. Several mechanisms for progressive enlargement of these cysts have been proposed, including hydrodynamic effects of the CSF, a ball-valve mechanism, and active or passive fluid transport.6,7,10,23,26,30 The symptoms and signs are mainly related to spinal cord or spinal nerve root compression. Thus, common presenting symptoms include local or radicular pain, sensory changes, motor paresis, and bladder disturbances.1-4,6-14,22-25 However, ACs of the CCJ may present with distinct clinical symptoms as a result of cerebellar, brain stem, or cervical spinal cord compression. These are very uncommon lesions and, until now, only six cases have been reported in the literature.5,17-21

Regardless of the location of the spinal ACs, clinical presentation is usually insidious and the symptoms and signs typically develop over a period of months or years.1,2,6,10,12,14,19,25,26 Intermittent exacerbations and remission of symptoms are also typical for these cases.4,7,8,10,13,22,24,25 According to the results obtained by reviewing the pertinent literature, three aspects of our case were unique when compared with all CCJ ACs. First, unlike this case presented in this report, all previously reported six cases had demonstrated extension between the posterior fossa and the upper cervical spine. second, the duration of symptoms (development of an AC in such a short duration) was significantly shorter in our case. Third, sudden onset life-threatening clinical deterioration was the most striking feature of our case.

Treatment

Because ACs are benign lesions, total surgical removal is the treatment of choice.3,4,7-9,11,14,19,23-25 Simple aspiration of the cyst will result in temporary relief of symptoms.4,6,7 Sometimes, complete removal cannot be carried out because of the location of the cyst, adhesion of the cyst wall to the surrounding neurovascular structures, or the size of the cyst.9,10,14,26 In these cases, fenestration into the adjacent spinal subarachnoid space,1,3,4,6-9,11,12,16,23,26,28 or shunting of the cyst into the peritoneum, pleura, or atrium, has been shown to be effective.1,9,13,26 Although there is a general agreement in the literature that asymptomatic ACs do not need surgical treatment, we think that surgical treatment may be considered for the ACs located at the CCJ (even if there is not any neurological finding) because of the possibility of expansion in a short duration and sudden onset clinical deterioration as in our case.

Conclusion

ACs of the CCJ are extremely rare lesions. Regarding its development and atypical clinical course, our case is distinctive compared with all other spinal intradural ACs. Although conclusive evidence concerning the pathogenesis of the cyst described in this report was not available, we urge readers to keep in mind the possibility of the development of this kind of AC.

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