Pineocytoma

Pineal parenchymal tumours range from pineocytoma (CNS WHO grade 1), through pineal parenchymal tumour of intermediate differentiation, to pineoblastoma (grade 4)^[1]. Pineocytoma, composed of well-differentiated cells forming pineocytomatous rosettes, is slow-growing and is often cured by complete resection. The pineal region also harbours germ-cell tumours (germinoma and non-germinomatous types), gliomas, meningiomas and benign pineal cysts, which are much more common and rarely need treatment, so a precise diagnosis is essential.

Compression of the cerebral aqueduct causes obstructive hydrocephalus, with headache, nausea, vomiting and papilloedema. Compression of the tectum causes Parinaud (dorsal midbrain) syndrome: upgaze palsy, convergence–retraction nystagmus and light–near dissociation of the pupils. Larger tumours cause ataxia and, rarely, hypothalamic or endocrine dysfunction.

MRI shows a well-defined pineal mass, often with cystic change and peripheral (“exploded”) calcification. The relationship to the vein of Galen, internal cerebral veins, basal veins of Rosenthal and tectum, and the steepness of the tentorium, guide the approach. MRI of the whole spine and CSF cytology are used to exclude dissemination. Serum and CSF alpha-fetoprotein and beta-hCG are measured in every patient: raised markers indicate a secreting germ-cell tumour, which is treated with chemotherapy and radiotherapy without resection^[2].

Hydrocephalus is treated first, preferably by endoscopic third ventriculostomy, during which a biopsy of the tumour and CSF sampling can be performed^[2]. When markers are negative, histological diagnosis is needed; stereotactic or endoscopic biopsy is possible, but open surgery provides both a definitive diagnosis from a larger sample and, for benign tumours such as pineocytoma, a cure through gross-total resection. Radiotherapy or radiosurgery is used for residual or recurrent tumour.

• Supracerebellar infratentorial approach: described by Krause and popularised in the microsurgical era by Stein, it uses gravity to drop the cerebellum and passes beneath the deep venous system, which then lies above the tumour^[3]. It suits midline tumours below the deep veins. A sitting or Concorde position is used.
• Occipital transtentorial approach: better for tumours that extend above the tentorium or laterally, or with a steep tentorium.
• Posterior interhemispheric transcallosal approach: for tumours extending into the third ventricle.
• Coagulate the bridging veins of the cerebellar surface; divide the arachnoid over the quadrigeminal cistern and identify the precentral cerebellar vein.
• Protect the internal cerebral veins, basal veins and vein of Galen at all times.
• In the sitting position, monitor for venous air embolism (precordial Doppler or transoesophageal echo).

Pineocytomas have an excellent prognosis after gross-total resection. Complications include transient or persistent eye-movement disorders, ataxia, venous infarction and, in the sitting position, air embolism and subdural or pneumocephalus. Parinaud syndrome often improves but may persist.