A 4-year-old boy sustained trivial head injury due to a fall from a bicycle. Immediately after the injury, he developed a scalp hematoma on the left side that resolved spontaneously. Three weeks later, he reported headache, vomiting, and squinting. Initially, he was treated at another hospital and then transferred to our institution 10 days later. Physical examination revealed left sixth cranial nerve palsy (Figure 1A) and bilateral papilledema (left > right). There were no other neurological or ophthalmological findings. Magnetic resonance imaging showed a large 10 × 8 cm unilocular cyst of the left middle cranial fossa encroaching on the ipsilateral Sylvian fissure and parasellar area (Figure 2). It was a thin-walled cyst containing a fluid isodense with cerebro-spinal fluid. These features were consistent with a Galassi type 2 arachnoid cyst.2 Diffuse bilateral sub-dural hygroma noted in the neuroimaging suggested the possibility of cyst rupture due to head injury, thereby precipitating the symptoms.
Clinical photograph showing left lateral gaze of the patient (A) before and (B) after surgical decompression of the arachnoid cyst.
(A) Coronal and (B) axial sections of T2-weighted magnetic resonance imaging showing the extent of the arachnoid cyst (black arrows) and subdural hygroma (white arrows).
A trial of acetazolamide (50 mg/kg/day) for a period of 6 days failed. On the seventh day at the hospital, a cysto-peritoneal shunt operation was performed. Intraoperative puncturing of the cyst caused gushing of clear fluid under great pressure. Postoperative recovery was uneventful. Sixth cranial nerve palsy resolved completely in 4 days (Figure 1B) and papilledema resolved gradually over 12 days. Follow-up neuroimaging after 6 weeks showed residual subdural hygroma and significant reduction in the size of the arachnoid cyst.
We searched PubMed, Indmed, Google Scholar, Embase, African Journals Online, and Scopus without any field, time, age, or language limits. We used a combination of key words such as “arachnoid cyst,” “abducens nerve,” “sixth cranial nerve,” “palsy,” “paralysis,” “strabismus,” “ocular symptoms,” “ophthalmic manifestations,” “esotropia,” and “lateral rectus palsy.” Two studies3,4 were excluded owing to inadequacy of details and one5 because of uncertainty of diagnosis. Of the two studies6,7 that described the same case, only the detailed description7 was considered for analysis. Thus, the comprehensive search identified only 12 additional cases of sixth cranial nerve palsy due to arachnoid cysts (Table 1).7–15
Review of Literature on SCNP due to Arachnoid Cyst
Sixth cranial nerve palsy secondary to arachnoid cysts is more common in children (54%) than in adolescents (23%) and young adults (23%) (Table 1). The youngest patient recorded was 3 months old.14 This pediatric skewing is not unexpected because 60% to 90% of arachnoid cysts are detected in childhood.2 A male preponderance also conforms to the epidemiology of arachnoid cysts in general. Sixth cranial nerve palsy and arachnoid cysts were ipsilateral in only 46% of cases. In the remaining cases, sixth cranial nerve palsy was either bilateral (27%) or contralateral (27%). Nearly 60% of ipsilateral sixth cranial nerve palsy was associated with features of raised intracranial pressure (eg, headache, vomiting, and papilledema). Thus, the pathogenic mechanism of sixth cranial nerve palsy in an arachnoid cyst is more likely attributable to a general increase in intracranial pressure rather than localized compression of the abducens nerve. However, the case reported by Jacob et al.13 could be an exception; in their patient, an arachnoid cyst of the right Meckel’s cave caused ipsilateral sixth cranial nerve palsy, probably due to direct compression of the sixth nerve.
Co-existence of subdural hygroma with sixth cranial nerve palsy and arachnoid cysts has special pathogenic and prognostic significance. This triad has been reported only twice before.10,15 Spontaneous or traumatic rupture of arachnoid cysts leads to subdural hygroma. The cyst fluid that ruptures into the subdural space is either absorbed (acute subdural hygroma) or persistent (chronic subdural hygroma leading to intracranial hypertension). Thus, acute subdural hygroma is a precursor to the spontaneous cure of sixth cranial nerve palsy if the palsy is due to direct compression of an arachnoid cyst. This phenomenon was reported by Jacob et al. in a pregnant woman.13 An intrapartum valsalva maneuver probably caused rupture of the arachnoid cyst and absorption resulted in spontaneous improvement of the abduction deficit. On the other hand, chronic subdural hygroma may precipitate sixth cranial nerve palsy by increasing intracranial pressure. All 3 patients with the triad (arachnoid cyst + subdural hygroma + sixth cranial nerve palsy) had a history of head injury and required surgical intervention. Thus, subdural hygroma is probably an indication for early surgical intervention when associated with sixth cranial nerve palsy.
Treatment of arachnoid cysts is controversial. Some physicians advocate surgical decompression of the cyst in the presence of mass effect. Others recommend non-surgical treatment because symptoms frequently persist even after surgery.1 Surgery of an arachnoid cyst resulted in complete resolution of sixth cranial nerve palsy in 54% of cases, partial recovery in 23% of cases, and no improvement in 23% of cases. These failures are attributable to delay in achieving cyst decompression9,11,12 or associated malformations.7,11,14 The delay between the onset of sixth cranial nerve palsy and effective surgical decompression of an arachnoid cyst ranges from 3 months9 to 3 decades.11 Association of mac-rocephaly11,14 is an indicator of poor prognosis because it implies a longstanding arachnoid cyst and thus a delay in treatment. Surgical options include craniotomy excision of the cyst, capsular resection, cysto-peritoneal shunting, endoscopic fenestration, or needle aspiration. Although cysto-peritoneal shunting is the most preferred procedure, there appears to be no correlation between the choice of operation and the outcome of sixth cranial nerve palsy. Early and effective decompression of an arachnoid cyst appears to be the key to success.
A delay of 6 to 12 months is usually recommended for the esodeviation to stabilize before proceeding to surgical correction of sixth cranial nerve palsy.6,7 Corrective prisms are prescribed during the waiting period. Nevertheless, in cases of sixth cranial nerve palsy secondary to an arachnoid cyst, we believe that early surgical decompression of the cyst should be preferred over delayed surgery of extra-ocular muscles or corrective prisms.