Serial MR imaging of pineal cysts: implications for natural history and follow-up

OBJECTIVE: The purpose of this study was to examine the frequency of change in size of pineal cysts on serial MR studies. MATERIALS AND METHODS: Thirty-two patients (19 females, 13 males) with a diagnosis of pineal cyst at any time who underwent brain MR imaging more than once in a period of at least 6 months were identified by computerized search of radiology reports. Four patients underwent MR imaging to follow up pineal cysts, whereas the remaining patients were imaged for a variety of indications, including intracerebral neoplasms. Measurements of maximal cyst dimension on both initial and latest follow-up studies were obtained in all patients, and cyst volumes were calculated in 23 patients. RESULTS: Length of follow-up ranged from 6 months to 9 years. All cysts were considered incidental and none were treated. Maximal cyst dimensions ranged from 0.5 to 2.2 cm. On average, there was no significant change in cyst volume. The maximal dimension of the cyst did not change in 24 (75%) of 32 patients. Two cysts resolved completely on follow-up, three cysts decreased by 2-4 mm, two cysts enlarged by 2-3 mm, and one cyst formed and grew to 1.2 cm. CONCLUSION: Whereas the size of pineal cysts as a whole remained unchanged on serial MR studies, cysts may either form or involute in individual patients. Small increases in cyst size did occur but were not associated with specific clinical findings. These findings suggest that typical pineal cysts may be followed up on a clinical basis alone rather than on imaging.