Brain abscess differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Farwa Haideri [2]


Brain abscess must be differentiated from metastatic tumors, necrotic tumors, and lymphomas.[1][2]

Differential Diagnosis

Brain abscess must be differentiated from:

Metastatic Tumor

  • The big differential is that the abscess is often located in watershed regions, and tumors often enhance diffusely with contrast.

Necrotic Tumor

  • Diagnosis of brain abscesses and necrotic tumors is often impossible without conventional MR imaging.[1]
    • Several studies demonstrate the utility of Diffusion-weighted imaging (DWI) to differentiate between necrotic or cystic lesions and brain abscesses.[3]
    • DWI has a sensitivity and specificity of over 90% for distinguishing abscess (low ADC) from necrotic tumors (high ADC).


  • Some studies suggest that indium scans can help differentiate abscess from CA, and thallium SPECT scans can distinguish CNS toxoplasmosis from lymphoma.[2]

Despite these differences, the true diagnosis is sometimes not made until biopsy.

Diseases Diagnostic tests Physical Examination Symptoms Past medical history Other Findings
Na+, K+, Ca2+ CT /MRI CSF Findings Gold standard test Neck stiffness Motor or Sensory deficit Papilledema Bulging fontanelle Cranial nerves Headache Fever Altered mental status
Brain tumour[4][5] Cancer cells[6] MRI Cachexia, gradual progression of symptoms
Delirium tremens Clinical diagnosis Alcohol intake, sudden witdrawl or reduction in consumption Tachycardia, diaphoresis, hypertension, tremors, mydriasis, positional nystagmus,
Subarachnoid hemorrhage[7] Xanthochromia[8] CT scan without contrast[9][10] Trauma/fall Confusion, dizziness, nausea, vomiting
Stroke Normal CT scan without contrast TIAs, hypertension, diabetes mellitus Speech difficulty, gait abnormality
Neurosyphilis[11][12] Leukocytes and protein CSF VDRL-specifc

CSF FTA-Ab -sensitive[13]

Unprotected sexual intercourse, STIs Blindness, confusion, depression,

Abnormal gait

Viral encephalitis Increased RBCS or xanthochromia, mononuclear lymphocytosis, high protein content, normal glucose Clinical assesment Tick bite/mosquito bite/ viral prodome for several days Extreme lethargy, rash hepatosplenomegaly, lymphadenopathy, behavioural changes
Herpes simplex encephalitis Clinical assesment History of hypertension Delirium, cortical blindness, cerebral edema, seizure
Wernicke’s encephalopathy Normal History of alcohal abuse Ophthalmoplegia, confusion
CNS abscess leukocytes >100,000/ul, glucose and protien, red blood cells, lactic acid >500mg Contrast enhanced MRI is more sensitive and specific,

Histopathological examination of brain tissue

History of drug abuse, endocarditis, immune status High grade fever, fatigue,nausea, vomiting
Drug toxicity Lithium, Sedatives, phenytoin, carbamazepine
Conversion disorder Diagnosis of exclusion Tremors, blindness, difficulty swallowing
Electrolyte disturbance or Depends on the cause Confusion, seizures
Febrile convulsion Not performed in first simple febrile seizures Clinical diagnosis and EEG Family history of febrile seizures, viral illness or gastroenteritis Age > 1 month,
Subdural empyema Clinical assesment and MRI History of relapses and remissions Blurry vision, urinary incontinence, fatigue
Hypoglycemia ↓ or Serum blood glucose


History of diabetes Palpitations, sweating, dizziness, low serum, glucose

Differentiating brain abscess in immunocompromised host

Brain abscess is common among immunocompromised patients who are at high risk for other fungal, bacterial, and viral infections. It should be differentiated from the following diseases:

Disease Differentiating signs and symptoms Differentiating tests
CNS lymphoma[14]
Disseminated tuberculosis[15]
Chagas disease[17]
CMV infection[18]
HSV infection[19]
Varicella Zoster infection[20]
Brain abscess[21][22]
Progressive multifocal leukoencephalopathy[23]
  • Symptoms are often more insidious in onset and progress over months. Symptoms include progressive weakness, poor coordination, with gradual slowing of mental function. Only seen in the immunosuppressed. Rarely associated with fever or other systemic symptoms
Differentiating brain abscess from other brain cystic lesions
Disease Prominent clinical features Lab findings Radiological findings
Brain abscess
  • Lumbar puncture is contraindicated but when done, it was variable between patients.
  • Culture from the CT-guided aspirated lesion helps in identifying the causative agent.
Brain tumors
  • CT may be used in localizing the tumor and getting a rough estimate on the dimensions.
  • MRI: Gadolinium-enhanced MRI is the preferred imaging modality for assessing the extension of the tumor and its exact location.[26]
Brain tuberculoma
  • Presentations are usually due to the pressure effect, not the T.B. bacilli.
  • Presenting symptoms and signs in order of occurrence:[27]
  1. Episodes of focal seizures
  2. Signs of increased intracranial pressure
  3. Focal neurologic deficits.
  • CT: Contrast-enhanced CT scan shows a ring enhancing lesion surrounded by an area of hypodensity (cerebritis) and the resulting mass effect.
  • MRI: Better than CT scan in assessing the site and size of the tuberculoma. Gadolinium-enhanced MRI shows a ring enhancing lesion between 1-5 cm in size (In NCC, the wall is thicker, calcifications are eccentric and the diameter is less than 2 cm)
  • 70% of the patients present with the neurological symptoms rather than the presentation of systemic disease. Common presentations are:[28]
  1. Cranial nerve neuropathies: Facial palsy is the most common presentation.
  2. Meningeal involvement: diffuse meningeal inflammation can cause diffuse basilar polyneuropathy in 40% of the patients. with neurosarcoidosis.
  3. Inflammatory spinal cord disease: Inflammatory span usually more than 3 spinal cord segments which helps to differentiate it from Multiple Sclerosis.
  4. Peripheral neuropathy: Asymmetric polyneuropathy or mononeuritis multiplex. It may also manifest as Guillain-Barré syndrome (GBS) like presentation.
  5. HPO axis involvement: may present as diabetes insipidus. More than 50% of the cases have no radiological signs.
MRI brain showing brain abscess - Case courtesy of A.Prof Frank Gaillard, From the case"
MRI brain showing Glioblastoma multiforme - Case courtesy of A.Prof Frank Gaillard, <a href=""></a>. From the case <a href="">rID: 28272</a>
MRI brain showing tuberculoma - Case courtesy of Dr G Balachandran, From the case"
MRI brain showing Neurosarcoidosis - Case courtesy of A.Prof Frank Gaillard, From the case


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