Papillary tumor of the pineal region

Papillary tumours of the pineal region (PTPR) are a relatively recently described entity, and considered one of four pineal parenchymal tumours under the current (2016) WHO classification of CNS tumours. 

Epidemiology

Papillary tumour of the pineal region are seen in a wide range of ages, reported from 1-70 years of age, with most cases found in middle age ^3,4. They are encountered equally in both genders ³.   

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

Papillary tumour of the pineal region are though to arise from specialised ependymocytes of the subcommissural organ located in the lining of the posterior commissure rather than from the pineal gland itself ^1-3. It is also hypothesised that some, or perhaps many, previously published descriptions of unusual pineal region tumours (e.g. choroid plexus papillomas and papillary ependymomas) actually represent PTPRs, as histologically they are difficult to distinguish, requiring immunohistochemistry ¹.

These tumours are considered WHO grade II or III tumours ³.

Macroscopic appearance

Papillary tumour of the pineal region are macroscopically indistinguishable from pineocytomas, appearing as well circumscribed tumours of the pineal region ³.

Microscopic appearance

Papillary tumour of the pineal region demonstrate varible morphology ranging from solid to predominantly papillary, reminiscent of ependymomas, including the presence of ependymal rosettes ³. Areas of necrosis are sometimes identified ^3,4.

Immunophenotype

PTPRs have a fairly characteristic immunohistochemical profile that allows them to be distinguished from other pineal parenchymal tumours.

• cytokeratins (AE1/3, CAM5.2, KL1, CK18): positive
• S100: positive
• vimentin: positive
• tansthyretin: positive
• neuron-specific enolase: positive
• MAP2: positive
• GFAP: variable

Radiographic features

MRI 

Papillary tumours of the pineal region are often indistinguishable from pineocytomas. Sometimes they demonstrate intrinsic high T1 signal attributed to secretory inclusions ^1,3. This is a relatively specific findings when other causes of T1 shortening are excluded (e.g fat in a teratoma or lipoma, melanoma, haemorrhagic metastases) ^1,3.

Screening of the entire neural axis is required as CSF dissemination has been reported in up to 7% of cases ⁴. 

Differential diagnosis

On imaging consider other pineal region masses, particularly:

• pineocytoma and pineal parenchymal tumour of intermediate differentiation: indistinguishable from each other based only on imaging and immunohistochemistry tests are required