Pineal Cyst
A pineal cyst is a benign, fluid-filled sac that develops in the pineal gland, a small endocrine gland located deep in the center of the brain. These cysts are remarkably common, found in up to 10% of the population on MRI scans, and are typically discovered incidentally during brain imaging performed for other reasons. The vast majority of pineal cysts are asymptomatic and require no treatment, though larger cysts can occasionally cause symptoms by compressing surrounding brain structures or obstructing cerebrospinal fluid flow.
What is it?
The pineal gland is a tiny, pine cone-shaped structure (hence its name) located in the epithalamus region, positioned between the two hemispheres of the brain near the center. This gland produces melatonin, a hormone that regulates sleep-wake cycles. A pineal cyst develops when fluid accumulates within or around the pineal gland, creating a thin-walled, fluid-filled structure. These cysts are thought to form due to degeneration or cavitation within the gland, though the exact mechanism remains unclear. Most pineal cysts are small (less than 1 centimeter) and remain stable in size over time.
Pineal cysts can occur at any age but are most commonly detected in young to middle-aged adults, with a slightly higher prevalence in women. The cysts appear as well-defined, round or oval structures on MRI that follow the signal characteristics of cerebrospinal fluid—bright on T2-weighted images and dark on T1-weighted images. The cyst wall may show thin rim enhancement with contrast administration. Most importantly, pineal cysts must be distinguished from other pineal region masses such as pineal tumors (pineoblastoma, pineocytoma), germ cell tumors, or other cystic lesions, which require different management. Characteristic imaging features and stability over time help confirm the benign nature of simple pineal cysts.
Important to Know
The overwhelming majority of pineal cysts are completely asymptomatic and discovered incidentally on brain imaging performed for headaches, head trauma, or other unrelated reasons. When symptoms do occur—which is rare and typically only with larger cysts (greater than 1.5-2 cm)—they result from mass effect on adjacent structures or obstruction of cerebrospinal fluid pathways. Potential symptoms include headaches (the most common symptom when present, though the relationship between pineal cysts and headaches remains controversial), visual disturbances such as blurred vision or problems with upward gaze (Parinaud syndrome) due to compression of the tectal plate, hydrocephalus if the cyst obstructs the cerebral aqueduct causing CSF buildup, and rarely, sleep disturbances or hormonal changes. Diagnosis is made through MRI, which provides detailed visualization of the cyst’s size, location, and characteristics. For asymptomatic pineal cysts, no treatment is needed, though some physicians recommend follow-up MRI in 6-12 months to confirm stability, after which no further imaging is typically necessary. For symptomatic cysts or those showing growth, treatment options include surgical cyst fenestration (creating an opening to drain the cyst), cyst excision, or endoscopic third ventriculostomy if hydrocephalus is present. The prognosis for pineal cysts is excellent—they are benign lesions with no malignant potential, and most patients with incidentally discovered pineal cysts can be reassured and require no intervention or follow-up.