W2 - Primary Neoplasms of the CNS - condensed

Question 1

In which age groups are primary CNS tumours most common?

Answer 1

Two peaks:

• 1st decade (0-10yo)
• 5th-6th decades (40-60yo)

Question 2

Which primary CNS tumours are common in adults?

Which primary CNS tumours are common in children?

Answer 2

Adults:

• 70% located supratentorial
• Glioblastoma multiforme (6th most common tumour in adults)

Children:

• 70% of CNS tumours in CNS arise in posterior fossa (cerebellar lesions common)
• Most of these are astrocytomas (45%) or neuroectodermal neoplasms (45%)

Question 3

How are primary CNS tumours classified?

Answer 3

May be classified:

Based on cell of origin (histogenetic classification)

• Neural tube (glioma, astrocytoma, oligodendroglioma)
• Neural crest (schwannoma, neurofibroma, meningioma)
• Embryonic remnants (melanoma, germinoma)

Benign vs malignant (rate of growth)

Primary or secondary

Question 4

How are astrocytomas classified?

Answer 4

Astrocytomas are derived from astrocytes. Most common primary CNS neoplasms.

• Grade I - Well differentiated (low grade)
• Grade II & III - Anaplastic
• Grade IV - Highly undifferentiated (high grade)

Question 5

Write brief notes on “Glioblastoma multiforme”

Answer 5

• Most common type of astrocytoma
• Classification: Grade IV (high grade) neoplasm = rapid growth, infiltrative, tumour cells show little/no differentiation
• Location: Midline of brain, form “butterfly tumour”
• Neovascularisation common
• Necrosis and haemorrhage common

Question 6

Write brief notes on “oligodendroglioma”

Answer 6

• Derived from oligodendroglia, but pure oligodendrogliomas rare (usually mixed tumour)
• Rare in children, 3% primary CNS neoplasms in adults
• Location: Cerebral hemispheres
• Classification: Less malignant than astrocytomas (slower growing)
• Can be identified by speckled calcification on X-Ray

Question 7

Define the following terms:

a) Choroid plexus papilloma

b) Medulloblastoma

Answer 7

a) Choroid plexus papilloma
A rare, benign tumour derived from ependymal cells that commonly affects the lateral ventricles.

b) Medulloblastoma
Primary, malignant CNS neoplasm derived from neurons that commonly affects children and are usually found in the midline cerebellar vermis.

Question 8

Write brief notes on the following primary CNS neoplasms which are derived from cells originating in the neural crest:

a) Meningioma
b) Schwannoma

Answer 8

a) Meningioma
- Origin: Arachnoid cap cells (of arachnoid villi)
- Frequency: 18% of intracranial neoplasms in adults (2:1 female/male ratio)
Common sites: Foramen magnum, olfactory groove and wing of sphenoid
- Biological behaviour: Usually benign, often infiltrates adjacent bone and dura

b) Schwannoma
- Origin: Schwann cells (in myelin sheath of cranial & spinal nerves).
- Frequency: 10-12% of primary CNS neoplasms in adults (more common in females)
- Site: Vestibular branch of CN VIII near cerebellopontine angle
- Biological behaviour: Benign (slow growing), well encapsulated.

Question 9

Briefly define the following terms:

a) Neurofibroma
b) Craniopharyngioma

Answer 9

Note: Neurofibromas and craniopharyngiomas are not neoplasms.

a) Neurofibroma
A benign tumour arising from the myelin sheath of spinal nerves that is composed of Schwann cells and fibroblasts that are usually found on the dorsal roots of spinal nerves.

b) Craniopharyngioma
A benign, well encapsulated tumour derived from ectodermal cells of Rathke’s pouch that is common in children and is usually located in the suprasellar region.

Question 10

a) Define the term “neurofibromatosis”.

b) Is it a common disease?

Answer 10

a) A pair of autosomal dominant disorders with a strong familial pattern of distribution, characterised by lesions in the skin, NS, bones, endocrine glands and viscera.
b) 1/3000-4000 (fairly common)

Question 11

List and describe the clinical manifestations of Type I (Peripheral) neurofibromatosis

Answer 11

Skin pigmentation
- Café-au-lait spots - Brown, freckle-like spots found in axilla (Crowe’s sign) and other intertriginous areas (groin, under breasts, knee and elbow creases) that appear at or shortly after birth.

Cutaneous tumors
- Soft, brown/purple mole-like papules found in the dermis that are tender and invaginate into the skin when pressed (button sign).

Subcutaneous tumours
2 types
- Neurofibromas - Firm, discrete nodules attached to a nerve
- Plexiform - An overgrowth of subcutaneous tissues, bone, skin, neurovascular fibromatous tissue

Miscellaneous manifestations

• Neurofibromas in dorsal roots of spinal & cranial nerves
• Scoliosis, bone cysts, cranial bone defects, bone hypertrophy and pathological bone fracture
• Glial tumours of CNS –> Intellectual impairment, hyperactivity, seizures
• Precocious (early onset) puberty
• Lisch nodule (Small, whitish spot on iris of eye)

Question 12

How is Type I (Peripheral) neurofibromatosis diagnosed?

Answer 12

At least 6 café-au-lait spots in one crease, with at least one being >1.5cm in diameter. Crowe’s sign (café-au-lait spots in axilla).