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41. Nonglial central nervous system tumors

Introduction

The following non-glial CNS tumors were mentioned in the lecture:

  • Neuronal and mixed neuronal-glial tumors
    • Dysembryoplastic neuroepithelial tumor (DNET) – grade I
    • Ganglioglioma/gangliocytoma – grade I
    • Central neurocytoma – grade II
  • Embryonal tumors
    • Medulloblastoma – grade IV
    • CNS primitive neuroectodermal tumor (PNET) – grade IV
    • Atypical teratoid/rhabdoid tumor (ATRT) – grade IV
  • Choroid plexus tumors
    • Choroid plexus papilloma – grade I
    • Atypical choroid plexus papilloma – grade II
    • Choroid plexus carcinoma – grade III
  • Meningiomas
    • Meningioma – grade I
    • Atypical meningioma – grade II
    • Anaplastic meningioma – grade III
  • Mesenchymal tumors
    • Haemangioblastoma – grade I
  • Primary CNS lymphomas
    • DLBCL
  • Tumors of the cranial and paraspinal nerves
    • Schwannoma – grade I
  • Tumors of the sellar region
    • Discussed in topic 42
  • Tumors of the pineal region
    • Pineocytoma – grade I
    • Pineoblastoma – grade IV
  • CNS metastases

Neuronal and mixed neuronal-glial tumours

The tumors belonging to this class originate from neurons (neuronal tumors), and some of them from both neurons and glial cells (mixed tumors). They’re low grade tumors.

Dysembryoplastic neuroepithelial tumor (DNET) is a grade I glioma. It’s most frequent in childhood and causes seizures. It has a good prognosis.

Ganglioglioma/gangliocytoma is a grade I glioma. It contains a mixture of neoplastic astrocytes and dysplastic neurons. It also often causes seizures. It has a good prognosis.

Central neurocytoma is a grade II glioma. They are often found close to the ventricular system.

Embryonal tumours

These tumors originate from remnants of embryonal stem cells in the brain. They’re all grade IV and therefore carry a very poor prognosis. These tumors are most frequent in childhood.

Medulloblastoma is the most important one. It’s the most common malignant tumor in childhood, accounting for one in every four cases. It most commonly occurs in the cerebellum, where it causes symptoms like ataxia. It often blocks the fourth ventricle, causing non-communicating hydrocephalus. Drop metastases into the spinal column are common and can cause paraplegia. Medullablastomas are extremly cellular and the individual tumor cells are small, hyperchromatic and little cytoplasm. Homer Wright/neuroblastic rosette can be seen and are characterized by primitive tumour cells surrounding central neuropil.

Primitive neuroectodermal tumors (PNET) are similar to medulloblastoma in histology but occurs in other parts of the CNS than the cerebellum. They are usually supratentorial (above the tentorium cerebelli). PNETs carry an even worse prognosis than medulloblastomas.

Atypical teratoid/rhabdoid tumor (ATRT) usually occur in the cerebellum, but they can occur anywhere in the CNS. The tumor cells resemble rhabdomyosarcoma, hence the name.

Meningioma

Meningiomas arise from arachnoid meningothelial cells and are most commonly grade I. They are the most common primary brain tumor, accounting for around one third of all cases. They may be asymptomatic and are therefore often incidental findings. They can arise in any part of the CNS with a meningeal covering but most commonly occur over the cerebral convexities.

Meningiomas are often attached to the dura mater, which they can also infiltrate into. They rarely infiltrate bone or the brain parenchyme.

We distinguish three types of meningioma, depending on the grade:

  • Meningioma – grade I
  • Atypical meningioma – grade II
  • Anaplastic meningioma – grade III

Multiple meningiomas are more common in people with neurofibromatosis type 2 (NF2), as are schwannomas and gliomas. Any person who develops more than one of these should be investigated for NF2.

Cranial and paraspinal tumours

These tumors arise from cranial or paraspinal nerves. The most common type is the schwannoma, a grade I tumor. It most commonly develops from the eighth cranial nerve, called vestibular schwannoma or acoustic neuroma. These arise from Schwann cells belonging to the vestibular nerve. The most common symptom is hearing loss.

Most are sporadic but they can be associated with NF2 as well.

Mesenchymal tumours

These tumors arise from the mesenchyme. The most common one is haemangioblastoma, a highly vascular neoplasm that is associated with von Hippel-Lindau disease. vHL disease is also associated with renal cancer, pheochromocytoma and pancreatic tumors. Haemangioblastoma usually occurs in the cerebellum.

CNS lymphomas

Lymphomas may arise anywhere, even in the CNS. The most common type of CNS lymphoma is diffuse large B-cell lymphoma (DLBCL). It is characteristic for immunosuppressed people, and it is the most common primary CNS tumor in this population. The tumors are often EBV positive.

Brain metastases

Metastases to the brain is the most frequent cause of brain tumors in adults. It commonly metastasizes from:

  • Lung cancer
  • Breast cancer
  • Melanoma
  • Renal cell carcinoma
  • Colorectal carcinoma

Metastases form sharply demarcated masses and cause oedema around. The oedema may increase the intracranial pressure. They commonly occur supratentorially at the grey matter-white matter junction.

Lung cancer accounts for most cases of brain metastases, simply because lung cancer is common. However, melanoma is the cancer which most often metastasizes to the brain.

Tumours of the pineal region

Tumors of the pineal region range from grade I (pineocytoma) to grade IV (pineoblastoma). These tumors are rare. They may cause hydrocephalus as they obstruct the third ventricle.

Choroid plexus tumours

These rare tumors develop from the choroid plexus, most commonly around the lateral ventricles. They range from grade I to grade III.