Rapidly Progressive Visual Loss Caused by a Sellar Arachnoid Cyst: Reversal With Transsphenoidal Microsurgery. (Case Histories).

ABSTRACT: Rapidly progressive vision loss is an uncommon presentation of a parasellar lesion. This report describes a patient with a sellar arachnoid cyst with suprasellar extension in whom rapidly progressive loss of vision was reversed by transsphenoidal microsurgical decompression and cyst fenestration. The differential diagnosis of cystic lesions of the sella and parasellar area is discussed, with emphasis on the importance of early intervention for vision recovery.

INTRACRANIAL ARACHNOID CYSTS account for less than 5% of all intracranial masses. (1-7) Arachnoid cysts (ACs) tend to occur within cerebrospinal fluid (CSF) cisternal spaces; approximately 10% are located in the parasellar region. The majority of ACs arise in the suprasellar cistern, displace the third ventricle, then extend either laterally toward the middle cranial fossa or superiorly toward the prepontine spaces. (1-3) Lesions in these areas cause symptoms and signs by slow enlargement and compression of the hypothalamus and optic apparatus and the intraventricular foramen, leading to headache, visual disturbances such as bitemporal hemianopsia and hydrocephalus. (1-7) Arachnoid cysts that arise within the sella are less common and tend to cause pituitary hypofunction by virtue of the empty sella syndrome, as well as slow development of visual problems as the cysts expand into the suprasellar area. (1-3) Rapid loss of vision is an uncommon presentation of parasellar lesions. (8) This report describes a pat ient with rapidly progressive visual loss and hypopituitarism. Vision was restored to normal by transsphenoidal microsurgical decompression and fenestration of a sellar AC.

CASE REPORT

A 74-year-old woman was seen in August 1999 with a 5-month history of decreasing visual acuity and visual field constriction in both eyes. She first noticed this decrease in visual acuity after cataract surgery on the left eye in April 1999. Formal visual field examination in May 1999 showed a bitemporal hemianopsia, worse on the left (Fig 1). Magnetic resonance imaging (MRI) was interpreted as showing diffuse atrophy. Over the course of the next 2 months, she had headaches, lethargy, generalized weakness, diminished libido, deceased short-term memory, and concentration difficulties; she did not have altered appetite or thirst, and her weight was unchanged. She was referred for evaluation. She had noticed significant constriction of her vision during the previous week. Visual field studies were repeated and showed substantial visual field constriction and tunnel vision (Fig 1). Review of the MRI obtained in May 1999 revealed a nearly empty sella that contained a cystic mass with suprasellar extension, The mas s did not enhance with contrast medium and was isointense with CSF on all image sequences; there was obvious distortion and elevation of the optic chiasm (Fig 2). Computed tomography (CT) with metrizamide confirmed the MRI findings; the cyst did not communicate with the other cisternae. Endocrine studies showed normal chemistry values, a serum osmolality level of 291 mOsm/kg (normal, 285 to 295 mOsm/kg), and urine specific gravity of 1.021. Other values were serum prolactin 29 ng/mL (normal, < 12 ng/mL), follicle stimulating hormone 10.8 mIU/mL (normal postmenopausal value 25 to 160 mIU/mL), growth hormone 0.1 ng/L (normal, 0.0 to 6.9 ng/L), somatomedin C 45 ng/mL (normal, 71 to 290 ng/mL), and cortisol 4.1 [micro]g/dL (normal, 10.4 to 26.4 [micro]g/dL). Thyroid function studies reflected the recent commencement of thyroxine therapy.

Because of the rapidly progressive visual loss, operation was done through a sublabial transseptal, transnasal approach to the sella. After the sellar floor and dura were opened, the compressed but otherwise normal pituitary gland was encountered, as expected from the preoperative MRI (Fig 2, B). The pituitary gland was split gently; clear CSF was encountered immediately. There was no solid tissue component, but rather a thin, diaphanous layer of arachnoid; this was stripped from the anterior, lateral, and superior aspects of the sella. Pathologic examination showed cytologically bland, flat, nonsqaumous epithelial cells consistent with arachnoid cells. Although the cistemogram (Fig 2, E) showed no connection of the CSF space with the cyst, even after a 4-hour delay, there was continuous egress of CSF at surgery. The sellar floor was occluded with an abdominal fat graft, covered by a portion of nasal bone, and then coated with tissue adhesive to seal off the opening. The nose was packed, and a lumbar drain wa s placed. Upon awakening, the patient believed her vision was improved. The lumbar drain and packing were removed late on postoperative day 5, and the patient was discharged the next morning. There was no leakage of CSF.

By the third postoperative month, the patient's vision had returned to normal (Fig 1, C), and headaches, fatigue, and lethargy had resolved. Some of her endocrine deficits had resolved, with a somatomedin C value of 82 ng/mL and cortisol value of 16.5 [micro]g/dL. Medications included thyroxine and synthetic estrogens. At 6 months after operation, she remained asymptomatic. She died in April 2000 of rupture of an abdominal aortic aneurysm.

DISCUSSION

Sellar and parasellar ACs are uncommon. The differential diagnosis of cystic lesions of the sella includes ACs, craniopharyngioma (CP), Rathke's cleft cysts (RCC), and cystic metastases to the pituitary or sella. (1-7) Most other lesions will have a solid component in addition to the cyst. Craniopharyngiomas, RCCs, and ACs are by far the most common lesions in this area. All three may prompt a similar constellation of neurologic complaints, as well as hydrocephalus, visual disturbances, and endocrinopathy. Common neurologic symptoms are headache and symptoms referable to hydrocephalus such as dizziness, seizure, poor concentration and memory, and coordination problems. (1-7) Visual changes are generally manifested as slowly progressive bitemporal hemianopsia. Endocrine abnormalities range from mild dysfunction such as hypothyroidism to panhypopituitarism with diabetes insipidus. (1,2,4) While all three pathologic types may have similar presentations, they can generally be differentiated by their radiographic characteristics: CPs tend to enhance, and both CP and RCC have differing signal characteristics on MRI, whereas ACs are isointense with the CSF on all imaging sequences and do not enhance. (4)

In a series of 53 cystic pituitary lesions reported by Shin et al, (1) 5 (9.5%) were ACs. No patient presented with rapid visual loss, but all patients with headache and visual disturbances had improvement; restoration of normal endocrine function was infrequent. In a 1987 report from the Mayo Clinic, 1,620 transsphenoidal operations were done over a period of almost 20 years; only 13 patients (0.08%) were found to have an AC. All 7 patients with visual loss had improved vision; however, as noted by Shin et al, (1) endocrine abnormalities were less likely to, resolve. (2) Twenty percent of patients have recurrence of AC, generally after 7 years or more. (3,4)

The pathogenesis of an intrasellar AC remains unclear. (9-11) One theory postulates herniation of an arachnoidal diverticulum through an incompetent diaphragma sella, the dural lining forming the roof of the sella. Alternatively, a diverticulum that forms within the arachnoidal layers progressively enlarges; this may develop beneath the diaphragma sella or invaginate through it. This latter hypothesis would preclude a communication with the remainder of the subarachnoid space. In our case, however, we encountered continuous flow of CSF intraoperatively, which favors the former hypothesis.

Although some authors suggest craniotomy, either from a pterional or subfrontal approach, or cystoperitoneal or ventriculoperitoneal shunting, most surgeons with experience using the transsphenoidal approach favor the latter as the most direct and least invasive method of decompressing and fenestrating the cyst. (2-4,6,7) It is the fenestration of the cyst walls that diminishes the likelihood of recurrence. (2-4,12)

As this case illustrates, however, exploration of an expanding lesion of the sella is imperative not only to establish a diagnosis, but also to relieve compression of the optic apparatus and the pituitary gland and parasellar structures. The surgical technique favored is transsphenoidal microsurgical exposure, decompression, and excision and marsupialization of the cyst wall. The results with respect to vision restoration are uniformly good.

CONCLUSION

Sellar ACs, though rare, represent an important cause of reversible vision loss. This report describes a woman whose dense tunnel vision, which developed slowly over at least 4 months in association with hypopituitarism and then rapidly progressed, was reversed by transsphenoidal microsurgical decompression and fenestration of an AC. Sellar and parasellar lesions causing vision loss are potentially reversible conditions that are important for physicians to recognize. The results with respect to visual function, as in this case, can be gratifying.

References

(1.) Shin JL, Asa SL, woodouse LJ, et al: cystic lesions of the pituitary: clinicopathological features distinguishing craniopharyngioma, Rathke's cleft cyst, and arachnoid cyst. J Clin Endocrinol Metab 1999;84:3972-3982

(2.) Meyer FB, Carpenter SM, Laws ER Jr: Intrasellar arachnoid cysts. Surg Neurol 1987;28:105-110

(3.) Baskin DS, Wilson GB: Transsphenoidal treatment of nonneoplastic intrasellar cysts. Neurosurgery 1984;60:8-13

(4.) Ross DA, Norman D, Wilson GB: Radiological characteristics and results of surgical management of Rathke's cysts in 43 patients. Neurosurgery 1992;30:173-178

(5.) Fahlbusch R, Paulus W, Huk W, et al: Surgical treatment of craniopharyngiomas; experience with 168 patients. J Neurosurg 1999; 90:237-250

(6.) Pierre-Khan A, Brauner R, Sainte-Rose C, et al: Presentation and management of suprasellar arachnoid cysts: review of 20 cases. J Neurosurg 1990; 73:335-359

(7.) Rappaport ZH: Suprasellar arachnoid cysts: options in operative management. Acta Neurochir 1993; 122:71-75

(8.) Chun BB, Lee AG, Coughlin WF, et al: Unusual presentations of sellar arachnoid cyst. J Neuroophthalmol 1998; 18:246-249

(9.) Harrison MJ, Post ED: Epithelial cystic lesions of the sellar and parasellar region: a continuum of ectodermal derivatives? J Neurosurg 1994; 80:1018-1025

(10.) Asa S: Atlas of Tumor Pathology. fascicle 22. Washington, DC, Armed Forces Institute of Pathology, 1998

(11.) Fox JL, AI-Mefty O: Suprasellar arachnoid cysts, an extension of the membrane of Liliequist. Neurosurgery 1980; 7:615-618

(12.) Jones RFC, Warnock TH, Nayanar V, et al: Suprasellar arachnoid cysts: management by cyst wall resection. Neurosurgery 1989; 25:554-561

KEY POINTS

* Rapidly progressive visual loss may be the result of compression of the optic chiasm.

* More common lesions of the the sella capable of causing optic compression include pituitary adenomas, craniopharyngiomas, metastic tumors, and arachnoid cysts.

* Arachnoid cysts can cause pituitary dysfunction, as well as visual loss.

* Arachnoid cysts are best treated with transsphenoidal microsurgery, which restores vision and pituitary function in most patients.