4 Natural History and Management Options of Pineal Cyst

Michael J. Mulcahy and Behzad Eftekhar

Abstract

A thorough understanding of the natural history and treatment options of pineal cysts is required for the neurosurgeon managing these patients, as the cysts are usually incidental, yet their critical location affords them catastrophic potential.

Pineal cysts are common incidental findings with contemporary neuroimaging. They are typically found in young adults (20–30 years of age) with a predilection for female (3:1 female-to-male ratio). Their reported prevalence varies from 1.3% (95% confidence interval [CI]: 1.0–1.6) to 23% (95% CI: 15.8–32.2) conditional to the methodology, sample size, and the quality of the magnetic resonance imaging (MRI) used.1^{,​ 2} The rate is much higher (20–40%) among autopsy studies³ and in children where size threshold among studies can be variable (2% prevalence for cysts  > 5 mm and up to 57% for cysts of any size).^{4,​ 5}

Pineal cysts are thought to arise from exaggeration of the microcysts that occur in the normal pineal gland.¹² Their importance arises from the difficulty in differentiating benign cyst from cystic tumors in the pineal region, especially when large or when there are atypical features. The classic histopathologic appearance describes a thin wall composed of three layers: a delicate fibrous external layer, a middle layer of pineal parenchyma, and an inner layer of glial tissue, often containing Rosenthal fibers.^{7,​ 13,​ 14}

On computed tomography (CT), pineal cysts appear as well-circumscribed fluid density lesions. The typical MRI appearance is of a thin-walled cyst with homogeneous contents that are isointense or slightly hyperintense to cerebrospinal fluid (CSF) on T1- and T2-weighted imaging, and slightly hyperintense to CSF on fluid-attenuated inversion recovery (FLAIR) weighted sequence.¹⁵ Septations are frequently present within the cyst. The thin, smooth wall can display contrast enhancement, thought to be due to the involvement of pineal tissue, which is outside the blood–brain barrier.^{16,​ 17} The cyst should be bereft of nodules (Fig. 4.1).

Most pineal cysts are small (< 1 cm) and asymptomatic. Larger cysts can cause a spectrum of clinical presentation secondary to hydrocephalus, Parinaud’s syndrome, or gaze paresis.^{6,​ 7,​ 8} Almost all published cases of symptomatic cysts have been greater than 1 cm in size. Headache, especially in the absence of hydrocephalus, is a controversial topic. Proposed mechanisms include intermittent obstruction of the aqueduct of Sylvius, abnormalities in melatonin secretion, or venous congestion from compression of the internal cerebral veins or the vein of Galen.^{9,​ 10,​ 11}

A thorough understanding of the natural history and treatment options is required of the surgeon managing patients with pineal cysts, as they are usually incidental and common, but they have a catastrophic potential because of their critical location.

4.2 Selected Papers on the Natural History of Pineal Cyst

●Nevins EJ, Das K, Bhojak M, et al. Incidental pineal cysts: is surveillance necessary? World Neurosurg 2016;90:96–102

The natural history of pineal cysts is not well understood. Many cysts are identified incidentally on MRI or at autopsy. However, there are cases of sudden death attributed to pineal cysts in the literature. In the first mortality attributed to a pineal cyst, a microscopic vascular malformation was found in the wall of a hemorrhagic pineal cyst; the term “pineal apoplexy” was thus coined.18 In addition, there are rare reports of sudden death attributed to compressive effects of the pineal cyst.^{19,​ 20,​ 21} Possible mechanisms could be transient obstruction of the aqueduct of Sylvius, or compression of the midbrain affecting the function of the reticular formation.

Pooled literature analysis on the natural history included nine retrospective studies (Table 4.1), encompassing a total of 735 patients with pineal cysts. Across a highly variable follow-up period ranging from 1 month to 16 years, 633 of the 735 (86.1%) cysts remained stable in size. Of the remainder, 36 (4.9%) increased in size, 40 (5.4%) decreased in size, and 4 (0.5%) cysts spontaneously resolved. No case of traumatic hemorrhage in a pineal cyst was found. Even cysts that increased in size often remained asymptomatic and did not require surgery. No patient who was being observed had an acute clinical deterioration or died secondary to the cyst.

Table 4.1 Natural history studies of pineal cysts

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