Neurology · Topic 9 of 22

Brain Tumors & Space-Occupying Lesions

Neurology · intracranial masses

Brain Tumors & Space-Occupying Lesions

Dexamethasone shrinks vasogenic edema around tumors; treat seizures but do not prevent them; a ring-enhancing lesion may be an abscess needing antibiotics and drainage.

Key numbers

Dexamethasone 4–8 mg/day for symptomatic edema4–8 mg/day (≥ 16 severe)

Brain abscess: ceftriaxone plus metronidazole, then drain4–8 weeks

Drain abscesses over 2 cm> 2 cm

01 · GiveDexamethasone 4–8 mg/day for symptomatic edema

For symptomatic peritumoral edema, start dexamethasone 4–8 mg/day; give 16 mg/day or more for severe symptoms of raised ICP. Dexamethasone is the steroid of choice (minimal mineralocorticoid effect).

02 · AvoidNo seizure prophylaxis in seizure-free tumor patients

Do not prescribe antiseizure prophylaxis to patients with newly diagnosed brain tumors or metastases who have never had a seizure (SNO/EANO Level A); evidence for perioperative prophylaxis is insufficient.

03 · GiveBrain abscess: ceftriaxone plus metronidazole, then drain

Treat brain abscess with ceftriaxone or cefotaxime plus metronidazole (add vancomycin after trauma, neurosurgery or endocarditis), usually with CT-guided aspiration or surgical drainage, for at least 4–8 weeks.

Causes & risk factors

Why it happens

Abscess organisms follow the sourceAbscesses from sinus or ear infection are often anaerobic or mixed (cover Bacteroides with metronidazole); after head trauma, neurosurgery or endocarditis suspect Staphylococcus aureus (add vancomycin).

Presentation

What you'll see

Tumors present with seizures, deficits, raised ICPBrain tumors present with headache and vomiting from raised ICP, new seizures, focal deficits or cognitive change; papilledema is present in only 25–35%, so its absence does not exclude raised ICP.

Abscess: ring enhancement; fever may be absentBrain abscess causes headache, lethargy, seizures and focal deficits over days to weeks, often without fever; contrast MRI with diffusion-weighted imaging shows a ring-enhancing mass that can mimic tumor.

Diagnosis & monitoring

Work-up

Metastases outnumber primary brain tumors 10 to 1Brain metastases are about 10 times more common than primary brain tumors and are usually multiple; a single surgically accessible metastasis is resected before radiation.

Taper dexamethasone as fast as toleratedTaper dexamethasone as rapidly as the patient tolerates on an individual plan; prolonged use brings weight gain, insomnia, proximal myopathy, hyperglycemia and adrenal insufficiency on withdrawal.

Do right now

In this order

First moves

Herniation from a mass: osmotherapy, dexamethasone, surgery

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Image with gadolinium-enhanced MRI

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Dexamethasone 4–8 mg/day for symptomatic edema4–8 mg/day (≥ 16 severe)

Why each step

Herniation from a mass: osmotherapy, dexamethasone, surgeryHerniation from a tumor: intubate, give mannitol or hypertonic saline plus IV dexamethasone, use brief hyperventilation (PaCO₂ 26–30 mmHg) only as a bridge, and decompress the mass surgically as soon as possible.

Image with gadolinium-enhanced MRINew seizures, focal deficits or signs of raised ICP warrant T1-weighted MRI with gadolinium (contrast CT if MRI unavailable), plus chest imaging to look for a primary when metastases are possible.

Dexamethasone 4–8 mg/day for symptomatic edemaFor symptomatic peritumoral edema, start dexamethasone 4–8 mg/day; give 16 mg/day or more for severe symptoms of raised ICP. Dexamethasone is the steroid of choice (minimal mineralocorticoid effect).

Management

Orders

Treat tumor seizures; levetiracetam preferredOnce a tumor patient has had a seizure, treat with an antiseizure medication; levetiracetam may be preferred over older agents because it causes fewer side effects (SNO/EANO, Level C).

Drain abscesses over 2 cmDrain solitary accessible abscesses, especially those over 2 cm; smaller abscesses may get antibiotics alone with serial MRI or CT every 2–3 days, draining any that enlarge.

Red flags & don'ts

Avoid harm

Suspected CNS lymphoma: no steroids before biopsy avoidIf imaging suggests primary CNS lymphoma, avoid corticosteroids before stereotactic biopsy whenever clinically possible — they rapidly kill lymphoma cells and can make the biopsy nondiagnostic.

No lumbar puncture with a mass lesion avoidDo not perform lumbar puncture in brain abscess or any mass lesion threatening herniation — removing CSF below can precipitate transtentorial herniation, and abscess CSF findings are nonspecific.

Brain tumor or brain abscess?

Commonly confused

Imaging	Enhancing mass with edema; metastases often multiple
Tissue diagnosis	Biopsy or excision; avoid steroids first if lymphoma suspected
Core treatment	Surgery and radiation; dexamethasone for symptomatic edema
Seizure prophylaxis	Not recommended if seizure-free
Lumbar puncture	Avoid when the mass threatens herniation

Commonly confused

Tell apart

Steroids treat vasogenic, not cytotoxic, edema must knowGlucocorticoids reduce vasogenic edema from a disrupted blood–brain barrier (tumor, abscess) but do nothing for cytotoxic edema (stroke, trauma), where the hyperglycemia they cause can worsen ischemia.

More detail

Reference

Show 5 reference facts

Metastases that tend to bleed: melanoma, renal cell carcinoma, choriocarcinoma, and thyroid, lung and breast cancers; hemorrhage can mimic a stroke.

Radiation for metastases: stereotactic radiosurgery for limited brain metastases in patients with good performance status; when whole-brain radiation is used in favorable-prognosis patients, add hippocampal avoidance and memantine.

In uncontrolled HIV or other immunosuppression, consider Toxoplasma gondii or fungal (e.g., Aspergillus) abscesses, which may need lifelong suppressive therapy.

In brain abscess with raised ICP, a short course of high-dose IV dexamethasone may help; antiseizure medications are frequently used to prevent seizures.

Radiation necrosis can appear as an enhancing mass indistinguishable from recurrent tumor on standard MRI; perfusion MRI, MR spectroscopy or FDG-PET help, and biopsy is diagnostic.

Pearl

Steroids work on the leaky edema of tumors and abscesses, not on the dead-cell edema of stroke or trauma.

Sources · Merck Manual Professional — Overview of Central Nervous System Tumors · Merck Manual Professional — Brain Herniation · Congress of Neurological Surgeons — Systematic Review and Evidence-Based Guidelines on the Role of Steroids in the Treatment of Adults With Metastatic Brain Tumors (Neurosurgery 2019) · Walbert T et al. SNO and EANO practice guideline update: Anticonvulsant prophylaxis in patients with newly diagnosed brain tumors. Neuro-Oncology 2021;23(11):1835–1844 · Primary central nervous system lymphomas: EHA-ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. HemaSphere 2024 · Merck Manual Professional — Brain Abscess · Anticonvulsant prophylaxis and steroid use in adults with metastatic brain tumors: summary of SNO and ASCO endorsement of the Congress of Neurological Surgeons guidelines. Neuro-Oncology 2019 · Farkas J. Internet Book of Critical Care (EMCrit) — Elevated intracranial pressure (ICP): lumbar puncture with focal mass lesions · Gondi V et al. Radiation Therapy for Brain Metastases: An ASTRO Clinical Practice Guideline. Pract Radiat Oncol 2022;12(4):265–282 (abstract via Europe PMC) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).