One of the most common referrals to Neurosurgeons is for evaluation of pineal cysts. The advent of widely available imaging such as MRI and CT scans has lead to a dramatic increase in findings such as this in patients who have presented often with very vague symptoms. As such they can be a diagnostic problem.
By definition a pineal cyst is a benign fluid containing cyst within the tissue of the pineal gland. These cysts are extremely common seen in 23% of adults undergoing MRI scan. Autopsy studies have shown a rate of 25-40%. They can be discovered at any age but tend to be found in middle age and older, possibly because of a higher rate of imaging in this demographic. Females are more likely to have a pineal cyst by a rate of 3 to 1.
Pineal cysts are almost always asymptomatic and found at imaging for an unrelated reason. Once thought by Descartes to be the set of the soul we now know the pineal gland produces melatonin, believed to be important in modulating sleep patterns. These functions are not affected by the presence of a cyst. In very rare cases a large cysts can cause blockage to the cerebral aqueduct and result in hydrocephalus. Even more rare is pineal apoplexy which is a sudden thunderclap headache from a bleed into the cyst cavity.
On imaging they are well defined round lesion usually less than 10mm and usually not loculated. The largest ever pineal cyst was 4.5cm! CT scans show a calcifed cyst wall in 25% of cases. 90% of pineal cysts enhance with gadolinium on MRI. Follow up scans usually show no change in size or characteristics over time.
The main differential diagnosis is of normal pineal gland or a pineocytoma. Pineocytomas are WHO grade 1 pineal parenchymal tumor but is usually solid or solid/cystic.
Pineal cysts are “leave me alone lesions”. In the very rare cases of hydrocephalus due to a pineal cyst aspiration or resection may be considered. If excised the tissue is soft tan/yellow with clear cyst fluid in the cavity.
In most cases the pineal cyst will not be the cause of the patients symptoms and reassurance and possibly a follow up scan will be offered. When appropriate, referrals to other specialities such as neurology or pain physicians may be required.