Brain Tumour MCQs (Part 1)

Explanation-

• PLAP (Placental alkaline phosphatase)– positivity indicates germ-cell differentiation
• Alpha-fetoprotein indicates the presence of yolk sac elements
• hCG positivity indicates the presence of syncytiotrophoblastic elements
• Vimentin is being called the “default” intermediate filament protein in CNS tumors
• Menigiomas typically exhibit EMA-positivity, a feature that helps in differential diagnosis with hemangiopericytoma

Explanation:

Most Common Glial Cell Tumor: Astrocytoma Most Common primary brain tumor: Glioma>Astrocytoma>Meningioma

Explanation:

• Pseudopapilledema may mimic papilledema in that the optic disc may appear swollen, but, unlike true papilledema, the peripapillary vessels are not obscured.
• It may be unilateral or bilateral.
• There are a number of benign conditions that can cause pseudopapilledema (including a small optic cup, buried disc drusen…), and extensive workup is generally not indicated

Explanation:

• On November 25, 1884, Mr. Rickman J. Godlee performed the first recognized resection of a primary brain tumor. This operation was carried out at the suggestion of Dr. A. Hughes Bennett
• Gliomas initially classified by Bailey and Cushing (1926)

Ref- The first primary brain-tumor operation- https://pubmed.ncbi.nlm.nih.gov/6387062/

All except D affect the 3rd nerve. But when pilocarpine is instilled, it acts directly on the muscarinic receptor (M3) found on the iris sphincter muscle, causing the muscle to contract and engage in miosis. If miosis does not occur with pilocarpine, it indicates that the muscarinic receptor on the the iris sphincter muscle is blocked – hence pharmacologic blockade is the answer.

A pharmacologically dilated pupil is very large (7–8 mm), and is larger than typical mydriasis due to third nerve compression (5–6 mm).

To differentiate pharmacologic pupil from a third nerve lesion: instill 1% pilocarpine (a parasympathomimetic) in both eyes (for comparison). A pharmacologic pupil does not constrict, whereas the normal side and a dilated pupil from a third nerve palsy will.

Explanation:

• The p53 protein is coded by a tumor suppressor gene on chromosome 17p 13.1.

Li-Fraumeni syndrome

• Rare (< 400 families identified) inherited autosomal dominant disorder of children and young adults with predominat soft-tissue sarcomas, osteosarcomas, breast cancer brain tumors and adrenocortical carcinoma.
• Usually caused by a germline mutation in the TP53 tumor suppressor gene on chromosome 17p13.
• There are 3 main sets of criteria for diagnosing Li-Fraumeni-like syndrome: LFL-E2 definition, LFL-B definition & the Chompret criteria.
• CNS tumors show a bimodal age distribution: 1) in children (primarily medulloblastomas & related embryonal tumors), and 2) in age 20–40 (primarily astrocytic neoplasms).

Explanation:

• Horner syndrome (HS) is caused by interruption of sympathetics to the eye and face anywhere along their path
• Includes Ptosis, Miosis, Enopthalmos, Anhydrosis, Loss of ciliospinal reflex
• The miosis (pupillary constriction) in Horner syndrome is only ≈ 2–3 mm. This will be accentuated by darkening the room, which causes the normal pupil to dilate.
• Ptosis is due primarily to paralysis of the superior and inferior tarsal muscles (weakness of the inferior tarsal muscle is technically called “inverse ptosis”)
• Enophthalmos is due to Müller’s muscle paralysis, which also contributes a maximum of ≈ 2 mm to the ptosis.
• Ptosis in HS is partial, c.f. complete ptosis, which is due to weakness of levator palpebra superioris, which is not involved in Horner syndrome.

Explanation:

• Hemianopia is impaired vision in half the VF of each eye; hemianopic defects do not cross the vertical meridian. Hemianopias may be homonymous or heteronymous. A homonymous hemianopia causes impaired vision in corresponding halves of each eye (e.g., a right homonymous hemianopia is a defect in the right half of each eye). Homonymous hemianopias are caused by lesions posterior to the optic chiasm, with interruption of the fibers from the temporal half of the ipsilateral retina and the nasal half of the contralateral retina. Vision is lost in the ipsilateral nasal field and the contralateral temporal field
• Lesions affecting the optic chiasm, such as pituitary tumors expanding out of the sella turcica, cause destruction of the fibers from both nasal hemiretinas and produce a heteronymous (opposite sides of the visual fields) hemianopia

It consists of a classical triad of

• Ipsilateral anosmia
• Ipsilateral optic atrophy
• Contralateral papilledema

Named after neurologist Robert Foster Kennedy.

Usually from olfactory groove or medial third sphenoid wing tumor (usually meningioma).

Now rare due to early detection by CT or MRI. Classic triad:

Occasionally ipsilateral proptosis will also occur due to orbital invasion by tumor.

Explanation:

• Histologically benign tumor of cranial nerve VIII located in the cerebellopontine angle (CPA)
• Usually arises from inferior division of the vestibular portion of the VIII nerve
• 3 most common early symptoms (clinical triad): hearing loss (insidious and progressive), tinnitus (high pitched) and dysequilibrium (true vertigo is uncommon)
• Histology: comprised of Antoni A (narrow elongated bipolar cells) and Antoni B fibers (loose reticulated)

Ref: Greenberg Textbook of Neurosurgery, 9th Edition, Chapter 40