Pineal cyst: results of long-term MRI surveillance and analysis of growth and shrinkage rates.

Objective: Pineal cyst (PC) is a relatively common true cyst in the pineal gland. Its long-term natural course remains ill defined. This study aims to evaluate the long-term natural history of PC and examine MRI risk factors for cyst growth and shrinkage to help better define which patients might benefit from surgical intervention.

Methods: The records and MRI of 409 consecutive patients with PC were retrospectively examined (nonsurgical cohort). Cyst growth and shrinkage were defined as a ≥ 2-mm increase and decrease in cyst diameter in any direction, respectively. In addition to size, MRI signal intensity ratios were analyzed.

Results: The median radiological follow-up period was 10.7 years (interquartile range [IQR] 6.4-14.3 years). The median change in maximal diameter was -0.6 mm (IQR -1.5 to 1.3 mm). During the observation period, cyst growth was confirmed in 21 patients (5.1%). Multivariate logistic regression analysis revealed that only age (odds ratio [OR] 0.96, 95% confidence interval [CI] 0.93-0.99, p < 0.01) was significantly associated with cyst growth. No patient required resection during the observation period. Cyst shrinkage was confirmed in 57 patients (13.9%). Multivariate analysis revealed that maximal diameter (OR 1.22, 95% CI 1.12-1.35, p < 0.01) and cyst CSF T2 signal intensity ratio (OR 9.06, 95% CI 1.38-6.62 × 101, p = 0.02) were significantly associated with cyst shrinkage.

Conclusions: Only 5% of PCs, mainly in patients younger than 50 years of age, have the potential to grow, while cyst shrinkage is more likely to occur across all age groups. Younger age is associated with cyst growth, while larger diameter and higher signal intensity on T2-weighted imaging are associated with shrinkage. Surgery is rarely needed for PCs, despite the possibility of a certain degree of growth.