Skin, CNS and Eye for NEET PG Pathology: Basal Cell Carcinoma, Squamous Cell Carcinoma, Melanoma, Meningitis CSF, Brain Tumours, Retinoblastoma

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🎯 Exam priority: High. Expect: CSF patterns of bacterial, viral and TB meningitis, organisms by age, Waterhouse-Friderichsen syndrome, the commonest skin cancer, BCC vs SCC, melanoma types and depth, astrocytoma grades, 1p/19q, meningioma in women, medulloblastoma site, and retinoblastoma genetics.

CBME mapping: PA 33.1–33.4, 34.1–34.3, 35.1. This closes the Pathology playlist; CSF examination basics are in article 16.

Meningitis CSF, skin tumours, brain tumours and retinoblastoma. Drawn by TrackNation.

Skin Tumours

• Basal cell carcinoma: the commonest skin cancer, in fair, sun-exposed skin (very rare in dark skin). A shiny papule that grows a pearly border with telangiectases and a central dell or ulcer. It invades locally but rarely metastasises.

• Squamous cell carcinoma: the second commonest; sun-exposed skin; may arise in an actinic keratosis, oral leukoplakia or a burn scar; commoner with chronic immunosuppression; metastasises in advanced stages. Keratoacanthoma: a firm round nodule with a central crater.

• Melanoma arises from melanocytes (skin, mucosa, eye, CNS); metastasis tracks the depth of dermal invasion. Superficial spreading (70%) — young adults, intermittent sun, often from a precursor nevus, BRAF V600; lentigo maligna melanoma (15%) — older adults, face; nodular (~5%). Warning signs: asymmetry, irregular border, mottled colour. Risks: many or atypical moles, giant congenital nevus > 20 cm, dysplastic nevus syndrome, CDKN2A (p16) mutations, immunosuppression.

• Kaposi sarcoma: endothelial tumour driven by HHV-8; far commoner with HIV or transplant immunosuppression.

Meningitis

• Bacterial: neonates — group B streptococci, E. coli, Listeria; older infants, children and young adults — N. meningitidis and S. pneumoniae. Hib, once the commonest, is now rare in the US and Western Europe. Meningococcal sepsis can cause bilateral adrenal haemorrhagic infarction — Waterhouse-Friderichsen syndrome.

• Viral: enteroviruses (summer, early autumn); lymphocytes with near-normal glucose. Chronic (≥ 4 weeks): TB, fungi (Cryptococcus in HIV), others — lymphocyte-predominant, low glucose, high protein.

CNS Tumours and Retinoblastoma

• Brain metastases are about 10 times commoner than primary tumours.

• Astrocytomas are the commonest gliomas: grade I pilocytic (and SEGA in tuberous sclerosis), II low-grade, III anaplastic, IV glioblastoma. Secondary glioblastomas carry IDH1/IDH2 mutations. Oligodendroglioma: 1p/19q codeletion — diagnostic, with longer survival and better treatment response.

• Meningioma: among the commonest intracranial tumours; the only brain tumour commoner in women; median age 67. Medulloblastoma: a primitive neuroectodermal tumour presenting as a posterior fossa mass with hydrocephalus; spreads through CSF.

• Retinoblastoma: children under 2; leukocoria (white pupil) and squint. Both alleles of RB1 (13q14) are lost — in hereditary cases one is germline and the second somatic (two-hit model). 40% bilateral, and bilateral disease is always heritable. A third of hereditary patients develop second cancers (sarcomas, osteosarcoma) within 50 years.

Traps the Examiner Sets

• BCC rarely metastasises; SCC can; melanoma spread depends on depth.

• Low CSF glucose + neutrophils = bacterial; low glucose + lymphocytes = TB/fungal; normal glucose + lymphocytes = viral.

• Neonatal meningitis: GBS, E. coli, Listeria — not meningococcus.

• Bilateral retinoblastoma = always hereditary; watch for osteosarcoma later.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 BCC Barely spreads; SCC Sometimes spreads; melanoma by depth — skin cancer spread

• 🧠 Newborn meningitis = 'GEL' (GBS, E. coli, Listeria) — neonatal meningitis

• 🧠 Low sugar + polys = bugs; low sugar + lymphs = TB/fungus; normal sugar + lymphs = virus — CSF

• 🧠 1p/19q = 'Oh, good' (oligodendroglioma, better outlook) — oligodendroglioma

• 🧠 Meningioma likes Madam (women) — meningioma

• 🧠 RB: two hits on 13; both eyes = born with it — retinoblastoma

Rapid-Revision Cards

• Commonest skin cancer

  Basal cell carcinoma.

• BCC look

  Pearly border, telangiectases, central dell.

• BCC spread

  Local invasion; rarely metastasises.

• SCC origins

  Actinic keratosis, leukoplakia, burn scar.

• SCC risk

  Chronic immunosuppression.

• Keratoacanthoma

  Firm nodule, central crater.

• Melanoma prognosis

  Depth of dermal invasion.

• Superficial spreading

  70%; young; nevus; BRAF.

• Lentigo maligna melanoma

  15%; older; face.

• Nodular melanoma

  ~5%.

• Melanoma gene (familial)

  CDKN2A (p16).

• Kaposi

  HHV-8; HIV, transplant.

• Neonatal meningitis

  GBS, E. coli, Listeria.

• Child/young adult meningitis

  Meningococcus, pneumococcus.

• Waterhouse-Friderichsen

  Meningococcal sepsis; adrenal haemorrhage.

• Bacterial CSF

  Neutrophils, low glucose, high protein.

• Viral CSF

  Lymphocytes, near-normal glucose.

• Chronic meningitis CSF

  Lymphocytes, low glucose; TB, fungi.

• Brain metastases

  ~10× primaries.

• Glioma grades

  I pilocytic/SEGA; IV glioblastoma.

• Oligodendroglioma

  1p/19q codeletion; better outlook.

• Meningioma

  Only brain tumour commoner in women.

• Medulloblastoma

  Posterior fossa; CSF spread.

• Retinoblastoma

  < 2 y; leukocoria; RB1 13q14; two hits.

• Bilateral RB

  Always heritable; osteosarcoma later.

Sources

Facts in this article were checked against these documents.

• MSD Manual Professional: Basal Cell Carcinoma; Squamous Cell Carcinoma; Keratoacanthoma; Melanoma; Kaposi Sarcoma — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• MSD Manual Professional: Acute Bacterial Meningitis; Viral Meningitis; Subacute and Chronic Meningitis — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• MSD Manual Professional: Overview of CNS Tumors; Gliomas; Meningiomas; Medulloblastomas; Retinoblastoma — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• Competency Based Undergraduate Curriculum, Pathology (PA 33–35) — National Medical Commission, 2024

Test Yourself: Practice Questions

Thirty questions in NEET PG style, most of them clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. The commonest skin cancer is

• (a) basal cell carcinoma

• (b) melanoma

• (c) Merkel cell carcinoma

• (d) squamous cell carcinoma

Q2. A fair-skinned person with long sun exposure has a slowly enlarging papule with a shiny pearly border, surface telangiectases and a central dell. The lesion

• (a) is basal cell carcinoma, which invades locally but rarely metastasises

• (b) is a benign keratoacanthoma

• (c) is melanoma with early spread

• (d) is squamous carcinoma always metastatic

Q3. A skin cancer develops in an old burn scar. The likely type is

• (a) melanoma

• (b) Kaposi sarcoma

• (c) basal cell carcinoma

• (d) squamous cell carcinoma

Q4. A patient on chronic immunosuppression is at particular risk of

• (a) seborrhoeic keratosis

• (b) basal cell carcinoma only

• (c) cutaneous squamous cell carcinoma

• (d) dermatofibroma

Q5. A firm round skin nodule with sharply sloping borders and a central crater is

• (a) melanoma

• (b) molluscum

• (c) keratoacanthoma

• (d) basal cell carcinoma

Q6. The single most important predictor of metastasis in cutaneous melanoma is

• (a) colour

• (b) patient sex

• (c) depth of dermal invasion

• (d) diameter alone

Q7. The commonest type of melanoma, often on a young woman's leg and often arising from a pre-existing nevus, is

• (a) lentigo maligna melanoma

• (b) nodular melanoma

• (c) acral lentiginous melanoma

• (d) superficial spreading melanoma (70%)

Q8. An elderly man has a melanoma arising in a freckle-like tan-brown macule on his chronically sun-exposed face. The type is

• (a) seborrhoeic keratosis

• (b) superficial spreading melanoma

• (c) basal cell carcinoma

• (d) lentigo maligna melanoma

Q9. A familial melanoma syndrome is linked to germline mutation of the tumour suppressor

• (a) RB1 only

• (b) APC

• (c) CDKN2A (p16)

• (d) VHL

Q10. Which skin lesion is a recognised melanoma risk factor?

• (a) a giant congenital melanocytic nevus over 20 cm

• (b) a cherry angioma

• (c) a skin tag

• (d) a seborrhoeic keratosis

Q11. Multicentric vascular skin tumours in a patient with advanced HIV arise from endothelial cells driven by

• (a) human herpesvirus 8

• (b) HPV 16

• (c) CMV

• (d) EBV

Q12. A 2-week-old has bacterial meningitis with neutrophils in the CSF. The likely organisms include

• (a) group B streptococci, E. coli and Listeria

• (b) enteroviruses

• (c) meningococcus and pneumococcus

• (d) Cryptococcus

Q13. In children and young adults, the commonest causes of bacterial meningitis are

• (a) Neisseria meningitidis and Streptococcus pneumoniae

• (b) Listeria and E. coli

• (c) Staphylococcus aureus

• (d) Hib only

Q14. A teenager with meningococcal sepsis develops coagulopathy and bilateral adrenal haemorrhagic infarction. This is

• (a) Addison disease from TB

• (b) Waterhouse-Friderichsen syndrome

• (c) Sheehan syndrome

• (d) Cushing syndrome

Q15. CSF that is turbid, under high pressure, with many neutrophils, high protein and a low CSF:blood glucose ratio suggests

• (a) viral meningitis

• (b) acute bacterial meningitis

• (c) multiple sclerosis

• (d) normal CSF

Q16. In summer, a young adult has meningitis; CSF shows lymphocytes, near-normal glucose and slightly raised protein. The likely cause is

• (a) enteroviruses

• (b) Cryptococcus

• (c) Mycobacterium tuberculosis

• (d) Neisseria meningitidis

Q17. A patient has meningitis for 5 weeks; CSF shows lymphocyte-predominant cells, low glucose and high protein. The likely group is

• (a) acute bacterial meningitis

• (b) viral meningitis

• (c) subarachnoid haemorrhage

• (d) chronic meningitis — TB or fungal

Q18. An HIV patient with low CD4 count develops chronic meningitis. The commonest fungal cause in this setting is

• (a) Aspergillus

• (b) Candida albicans

• (c) Cryptococcus neoformans

• (d) Histoplasma

Q19. Compared with primary brain tumours, brain metastases are

• (a) seen only in children

• (b) rarer

• (c) about 10 times more common

• (d) equally common

Q20. The commonest type of glioma is

• (a) astrocytoma

• (b) ependymoma

• (c) medulloblastoma

• (d) oligodendroglioma

Q21. A WHO grade IV astrocytic tumour is

• (a) glioblastoma

• (b) subependymal giant cell astrocytoma

• (c) anaplastic astrocytoma

• (d) pilocytic astrocytoma

Q22. A frontal-lobe glioma shows codeletion of 1p and 19q. This points to

• (a) glioblastoma

• (b) meningioma

• (c) medulloblastoma

• (d) oligodendroglioma with a better prognosis

Q23. Secondary glioblastomas typically carry mutations in

• (a) VHL

• (b) RB1

• (c) BRAF V600E

• (d) IDH1 or IDH2

Q24. A child with tuberous sclerosis has a grade I astrocytic tumour near the ventricles. It is

• (a) oligodendroglioma

• (b) ependymoma

• (c) subependymal giant cell astrocytoma

• (d) glioblastoma

Q25. The only brain tumour more common in women is

• (a) medulloblastoma

• (b) primary CNS lymphoma

• (c) glioblastoma

• (d) meningioma

Q26. A patient presents with a posterior fossa mass and obstructive hydrocephalus; the tumour can spread through CSF. The likely tumour is

• (a) glioblastoma

• (b) meningioma

• (c) craniopharyngioma

• (d) medulloblastoma

Q27. An 18-month-old's photo shows a white pupillary reflex in one eye, and the child has a squint. The likely diagnosis and gene are

• (a) congenital cataract — no gene

• (b) retinoblastoma — RB1 on 13q14

• (c) neuroblastoma — MYCN

• (d) retinopathy of prematurity

Q28. In hereditary retinoblastoma, tumour develops when

• (a) one allele is mutated only

• (b) a germline RB1 mutation is followed by a somatic mutation of the other allele

• (c) both alleles are normal

• (d) RB1 is amplified

Q29. A child has retinoblastoma in both eyes. This disease is

• (a) caused by HPV

• (b) never heritable

• (c) always heritable

• (d) usually acquired from radiation

Q30. A survivor of hereditary retinoblastoma is at increased risk of which later cancer?

• (a) osteosarcoma

• (b) papillary thyroid carcinoma

• (c) Hodgkin lymphoma

• (d) seminoma

Active Recall

From memory: contrast basal and squamous cell carcinoma; give melanoma types, risk factors and the main prognostic factor; name Kaposi sarcoma's cause; give meningitis organisms by age and the CSF pattern of bacterial, viral and chronic meningitis; describe glioma grades, oligodendroglioma genetics, meningioma and medulloblastoma; and explain retinoblastoma genetics and presentation.