Pineoblastoma

A pineoblastoma is a tumour which is closely related to PNETs and medulloblastomas but found in the pineal region. 

Pathology

The tumour originates from neuroectodermal cells. It is the least differentiated pineal cell tumours, with pineocytomas and pineal parenchymal tumour with intermediate differentiation representing better differentiated tumours along the same spectrum, and are considered WHO grade IV tumours. 

Associations

When associated with bilateral retinoblastomas thery are known as trilateral retinoblastoma.

Demographics and clinical presentation

They are typically found in young children, with both sexes being equally affected (in contrast to the male predominance seen in pineal germinomas). 

They are typically large and almost always associated with obstructive hydrocephalus, due to compression on the aqueduct. Compression of the tectal plate may also result in the Parinaud syndrome.  

They are highly malignant tumours prone to CSF seeding, which is present in 15% of patients at the time of diagnosis.

Radiographic features

Pineoblastomas tend to be large poorly defined masses, with frequent CSF seeding at presentation. They have a tendency to directly involve adjacent brain structures, which helps distinguish them from other pineal tumours which tend to be better circumscribed. 

Classically, they are described as having peripherally disperse or "exploded" calcification (Mnemonic: blasted calcification), similar to pineocytomas. In contrast pineal germinomas tend to engulf pineal calcification.

CT

The solid component tends to be hyperdense on CT, similar to germinomas, due to high cellularity. 

Differential diagnoses

• other pineal parenchymal tumours
  • pineocytoma : mature well-differentiated tumor : smaller and better circumscribed
  • pineal parenchymal tumour with intermediate differentiation
  • papillary tumour of the pineal region
• germ cell tumours
  • germinoma
    • marked male predominance
    • engulfed calcification
      
  • embryonal carcinoma
  • choriocarcinoma
  • teratoma : may contain fat
• astrocytoma of pineal gland
• metastasis
• pineal cyst : at most thin (<2mm) peripheral enhancement