Leptomeningeal carcinomatosis (carcinomatous meningitis)

Cancer of unknown primary is biopsy-confirmed metastatic cancer for which a standardized evaluation fails to identify the primary site, accounting for 2% to 6% of invasive cancers. Sorting patients into a favorable subgroup (germ cell, lymphoma, breast, ovarian, or head and neck pattern) against the unfavorable majority (survival 4-10 months) drives whether treatment aims for cure or palliation.

Paraneoplastic syndromes are remote effects of tumor-derived hormones, antibodies, and cytokines rather than direct invasion, and they often announce an occult cancer before it is otherwise detectable.

Malignant spinal cord compression (metastatic epidural spinal cord compression) is an oncologic emergency from vertebral metastasis that requires whole-spine MRI within 24 hours, immediate high-dose dexamethasone, and urgent radiotherapy or surgical decompression to prevent irreversible paralysis.

Spinal cord compression is mechanical narrowing of the spinal canal by tumor, hematoma, abscess, disc herniation, or trauma that produces myelopathy; it is a neurologic emergency requiring urgent MRI of the affected level and immediate treatment of the cause, since surgical decompression rarely restores function once paraplegia develops.

Cauda equina syndrome is compression of the lumbosacral nerve roots below the spinal cord causing saddle anesthesia, bladder or bowel dysfunction, bilateral leg weakness with areflexia, and low tone, most often from a large central lumbar disk herniation. It is a surgical emergency diagnosed by emergent MRI of the lumbar spine and treated with urgent decompression.

Breast cancer is a malignancy of ductal or lobular epithelium, most often presenting as a firm, painless mass in the upper outer quadrant. Diagnosis rests on core needle biopsy with estrogen, progesterone, and HER2 receptor testing, and first-line treatment pairs breast-conserving surgery or mastectomy with sentinel node biopsy, radiation, and receptor-guided systemic therapy such as tamoxifen or trastuzumab.

Lung cancer is the leading cause of cancer death worldwide, split into non-small cell lung cancer (NSCLC, 80% of cases: adenocarcinoma, squamous cell, large cell) and small cell lung cancer (SCLC, 10-15%), both driven overwhelmingly by cigarette smoking. Diagnosis requires tissue histopathology, staging drives treatment (TNM staging for NSCLC, limited versus extensive stage for SCLC), and management ranges from lobectomy in early-stage disease through concurrent chemoradiation and consolidation immunotherapy in locally advanced disease to targeted tyrosine kinase inhibitors, immune checkpoint inhibitors, or platinum-based chemotherapy in metastatic disease.

Melanoma is a malignant tumor of melanocytes recognized by the ABCDE criteria (asymmetry, border irregularity, color variation, diameter greater than 6 mm, evolving) and confirmed by complete excisional biopsy that captures full lesion thickness. Treatment starts with wide local excision sized to the Breslow tumor depth, adds sentinel lymph node biopsy for deeper lesions, and escalates to BRAF/MEK-targeted therapy or checkpoint immunotherapy for metastatic disease.

Acute lymphoblastic leukemia is a clonal proliferation of lymphoid precursor blasts that replace the bone marrow, the most common cancer in children, diagnosed when TdT-positive lymphoblasts make up 20% or more of the marrow and classified by flow cytometry immunophenotype and cytogenetics. Treatment is multi-phase chemotherapy (induction, consolidation, CNS prophylaxis, maintenance for up to 2 years), with a tyrosine kinase inhibitor added for Philadelphia-chromosome-positive disease and aggressive tumor lysis prophylaxis at the start of therapy.

Non-Hodgkin lymphoma is a heterogeneous group of B-cell (about 85%) and T-cell lymphoid malignancies that spread noncontiguously and often involve extranodal sites, ranging from indolent follicular lymphoma to aggressive diffuse large B-cell lymphoma to highly aggressive Burkitt lymphoma. Diagnosis requires excisional or core biopsy with flow cytometry and cytogenetics, Ann Arbor staging with PET-CT, and treatment is subtype-specific, from observation to R-CHOP to intensive Burkitt regimens with aggressive tumor lysis and CNS prophylaxis.

Hodgkin lymphoma is a B-cell malignancy defined by Reed-Sternberg cells that classically presents with painless, contiguously spreading cervical or mediastinal lymphadenopathy in a young adult, and it is confirmed by excisional lymph node biopsy. Ann Arbor/Lugano stage and interim PET response drive risk-adapted ABVD chemotherapy with or without radiation, and most patients are cured.

In adults, brain metastases (lung, breast, kidney, melanoma) are the most common intracranial tumors, meningioma is the most common primary tumor, and glioblastoma multiforme is the most aggressive primary glioma. Management combines resection when feasible, radiation, and chemotherapy (temozolomide for glioblastoma, methotrexate-based regimens for CNS lymphoma) with corticosteroids and antiepileptics for symptom control.

Guillain-Barre syndrome is an acute, post-infectious autoimmune polyradiculoneuropathy causing rapidly progressive ascending flaccid weakness and areflexia. Diagnosis is clinical, supported by albuminocytologic dissociation on CSF and demyelinating changes on electrodiagnostic studies; first-line treatment is IVIG or plasma exchange with close monitoring for respiratory failure.

Idiopathic intracranial hypertension (formerly pseudotumor cerebri) is raised intracranial pressure of unclear cause, without a mass lesion or hydrocephalus, occurring mainly in obese women of childbearing age and presenting with headache, papilledema, and visual symptoms. Diagnosis requires an elevated lumbar puncture opening pressure with normal CSF and normal or empty-sella imaging; treatment centers on weight loss and acetazolamide to protect vision, with surgery reserved for medically refractory disease.

Cryptococcal meningoencephalitis is the most common cause of fungal meningitis worldwide, driven by CNS dissemination of inhaled Cryptococcus in an immunosuppressed host, typically HIV with a CD4 count under 50; treatment is induction amphotericin B plus flucytosine, consolidation and maintenance fluconazole, and aggressive lowering of elevated intracranial pressure.

Viral meningitis is an acute lymphocytic-predominant meningeal infection, most often caused by enteroviruses, that presents with fever, headache, and neck stiffness milder than bacterial meningitis; diagnosis rests on CSF analysis and PCR, and management is supportive care after empiric antibacterial and, when HSV cannot be excluded, IV acyclovir coverage is stopped.

Sarcoidosis is a multisystem granulomatous disease of unknown cause defined by noncaseating granulomas, most commonly involving the lungs and hilar lymph nodes. Most patients are asymptomatic or have a self-limited course staged by chest radiograph; symptomatic organ-threatening disease is treated with systemic glucocorticoids, with methotrexate or another steroid-sparing agent added for glucocorticoid-refractory or glucocorticoid-intolerant disease.