Pineocytoma

Pineocytomas are a relatively benign pineal parenchymal tumour that have a relatively good prognosis.

On imaging, they generally appear as a well-demarcated tumour with less than 3 cm, iso to hyperattenuating on CT, hypo to isointense on T1, and hyperintense on T2. An avid and homogeneous enhancement is characteristic. Cystic changes may be present, which in some cases, can make difficult the differentiation from a pineal cyst. 

Epidemiology

Pineocytomas can be encountered at any age but mostly occur in young adults in the second decade(20-60 years of lifeage) ^5,79. Unlike pineal germinomas both genders, which have a strong predilection for males, pineocytomas are equally affectedsomewhat more frequently encountered in females (M:F 0.6:1)⁹.

Clinical presentation

As with all other pineal region masses, clinical presentation is mainly from obstructive hydrocephalus secondary to compression of the tectum of the midbrain and obstruction of the aqueduct. Compression of the superior colliculi can also lead to a characteristic gaze palsy, known as Parinaud syndrome.

Pathology

Pineocytomas are well-differentiated tumours and  consideredconsidered a WHO grade I tumours (or sometimes grade II lesions - depending onin the source ⁷ - see current WHO classification of CNS tumours), believed to arise from pinealocyte ⁹.

Macroscopic appearance

These tumours are well circumscribed, with cystic or haemorrhagic change sometimes evident ⁹. They have a grey or tan cut surface.

Microscopic appearance

Under light microscopy, pineocytomas are composed of small cells similar in appearance to normal pinealocytes, arranged in sheets; pineocytomatous pseudorosettes are characteristic and not seen in normal pineal gland tissue ⁹.

As is the case with the rest of the pineal gland, pineocytomas do not have a well-formed blood brain barrier and as such enhance vividly with contrast ⁶. Under light microscopy

Immunophenotype

• synaptophysin: positive
• NFP: positive
• neuron-specific enolase: positive
• other neuronal markers (e.g. MAPT, pineocytomatous pseudorosettes are characteristic.chromogranin-A, 5-HT etc..): variable
• NeuN: negative

Radiographic features

Typically pineocytomas are slow growing and well-circumscribed tumours (compared to pineoblastomas that tend to be larger, and less well circumscribed-circumscribed). They tend to be solid, although focal areas of cystic change, or haemorrhage do occur. When the cystic component is large, distinguishing them from pineal cysts can be difficult, although it has been postulated that this is not so much the case if complete and accurate imaging is obtained (i.e. good quality thin section MRI with contrast) ⁶. 

CT

CT demonstrates the mass to be of intermediate density, similar to the adjacent brain. Pineal calcifications tend to be dispersed peripherally. This is the same pattern seen in other pineal parenchymal tumours, which is helpful in distinguishing these tumours from pineal germinomas that tend to 'engulf' pineal calcification. 

MRI

MRI is the modality of choice for examining tumours of the pineal region. 

• T1: hypo to isointense to brain parenchyma
• T2
  • solid components are isointense to brain parenchyma
  • areas of cystic change are common
  • sometimes the majority of the tumour is cystic
• T1 C+ (Gd): solid components vividly enhance

Treatment and prognosis

Pineocytomas are treated surgically and have an excellent prognosis when a complete resection is achieved (which is most of the time as they are well-circumscribed lesions). A 5-year survival of 86% has been reported ⁷. 

Local recurrent and even CSF metastases are reported, but rare ⁵. 

Differential diagnosis

On CT or MRI consider:

• pineal cyst
  • at most thin smooth (<2 mm) peripheral enhancement
• other pineal parenchymal tumours
  • pineal parenchymal tumour with intermediate differentiation
  • pineoblastoma: larger, poorly defined
  • papillary tumour of the pineal region
• germ cell tumours
  • germinoma
    • marked male predominance
    • engulfed calcification
  • embryonal carcinoma
  • choriocarcinoma
  • teratoma: may contain fat
• astrocytoma of the pineal gland
• metastasis