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Pineal cyst

Pineal cysts are common, usually asymptomatic, and typically found incidentally. Their importance is mainly in the fact that they cannot be distinguished from cystic tumours, especially when large or when atypical features are present. As such, many patients undergo prolonged followup for these lesions, presumably with associated anxiety. 

Epidemiology

Pineal cysts are typically found in young aged adults (20-30 years of age) with a predilection for women (3:1 female to male ratio). They are seen in approximately 5% of brain MRIs and 20-40% of autopsy series. 

Clinical presentation

The vast majority of pineal cysts are small (<1 cm) and asymptomatic. When larger they can present with mass effect on the tectal plate leading to compression of the superior colliculi and Parinaud syndrome. If the cerebral aqueduct is compressed, they may also result in obstructive hydrocephalus. Rarely, haemorrhage in to a pineal cyst can cause rapid expansion and so called pineal apoplexy

Pathology

Pineal cysts are composed of three concentric layers:

  • inner layer: finely fibrillar glial tissue often containing hemosiderin
  • middle layer: pineal parenchyma +/- calcification
  • outer layer: thin fibrous connective tissue

As they are most frequently seen in young women, it has been suggested that hormonal changes play a part in their formation. As these women get older the cyst initially enlarges and then shrinks. In males, they tend to remain stable over time.

The cyst typically contains proteinaceous fluid which as a result does not follow CSF on imaging.

As is the case with the rest of the pineal gland, the walls of pineal cysts do not have a well formed blood brain barrier and as such can enhance vividly with contrast 5

Radiographic features

CT

Well circumscribed fluid density lesions with thin rim calcification seen in ~25%. Some peripheral enhancement is also often seen. The internal cerebral veins are elevated and splayed by the cyst.

MRI
  • T1:
    • typically iso to hypo intense compared to brain parenchyma
    • 55 - 60% are somewhat hyper intense when compared to CSF
    • generally homogenous in signal
  • T2:
    • high signal 
    • usually slightly hypointense to CSF
  • FLAIR: often does not attenuate fully
  • DWI / ADC: they demonstrate no restricted diffusion
  • T1 C+ (Gd):
    • approximately 60% of lesions enhance
    • enhancement is usually thin (< 2mm) and confined to the rim (either complete or incomplete)
    • it is important to note that if post contrast imaging is delayed (60-90min), gadolinum may diffuse into the cyst fluid and may lead to the mass appearing solid
    • in atypical cases enhancement may be nodular, or there may be evidence of previous haemorrhage into the cysts

Treatment and prognosis

In almost all cases no treatment is necessary, and in most cases, provided the cyst is small, then no imaging follow-up is required. 

In a study of 32 patients with pineal cyst, followed up from 6 months to 9 years, found cyst enlargement in only 3 patients, 75% remaining the same, and the rest shrinking. The authors conclude that cysts with typical features may be followed up clinically, rather than with imaging 2.

When cysts are above 10-12mm in diameter follow-up imaging may be necessary as a cystic pineocytoma may appear similar. 

Differential diagnosis

Unfortunately, especially in the setting of nodular enhancement or incomplete imaging it is not possible to distinguish a cystic pineocytoma from a pineal cyst on imaging alone, although if thorough imaging is carried out most cases can be sorted out 5. If a cyst is larger than 10-14mm many would advocate follow-up to ensure stability over time, although this is contentious. 

Additionally there are several other neoplasms which may arise in the pineal region, such as germ cell tumours (germinoma, embryonal carcinoma, choriocarcinoma, teratoma), pineocytoma, and metastases. These tumours may contain cystic elements, and several are highly malignant, making follow-up of a large or atypical cyst necessary.

The differential therefore includes:

For a more complete list see pineal mass article


Related articles

Pineal region masses

The pineal region is anatomically complex and plays host to a number of unique masses and tumours as well as potentially affected by many entities seen more frequently elsewhere in the brain. 

General reading
Pathology 

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