Autoimmune Encephalitis CT
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Julinka Auta Fernandes
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Overview
Autoimmune encephalitis has no specific diagnostic computed tomography (CT) appearance. Brain CT has limited sensitivity for autoimmune encephalitis, and a normal scan does not exclude the disease. In an acute presentation, head CT is principally useful for investigating alternative structural causes of symptoms or major intracranial complications.[1][2]
CT of the chest, abdomen, and pelvis has a separate role in investigating an associated neoplasm in appropriate adults. Finding a tumor can support a paraneoplastic explanation in the correct clinical setting, but does not by itself establish autoimmune encephalitis.[3]
Key CT Findings in Autoimmune Encephalitis
Head CT
In autoimmune encephalitis, head CT may be normal despite clinically significant disease. There is no CT pattern that reliably identifies a particular neuronal antibody or establishes the diagnosis.[1]
For an adult presenting with altered mental status and suspected intracranial pathology or a focal neurological deficit, the American College of Radiology rates noncontrast head CT as usually appropriate initial imaging. This is emergency assessment guidance, rather than a recommendation that CT can diagnose autoimmune encephalitis.[2]
The principal questions include whether there is:
- Intracranial hemorrhage.
- A large intracranial mass or substantial mass effect.
- Hydrocephalus.
- Another major structural abnormality that could explain the presentation.
An abnormality requires interpretation on its own merits. It should not automatically be attributed to autoimmune inflammation, and a normal scan does not end the encephalitis investigation.[2][1]
Contrast-Enhanced Body CT
In autoimmune encephalitis, contrast-enhanced CT of the chest, abdomen, and pelvis is a reasonable initial neoplasm-screening investigation in appropriate adults. It can locate a mass and define its extent, helping plan biopsy or subsequent specialist assessment.[3]
Relevant associated tumors include small cell lung cancer, thymic neoplasms, breast cancer, ovarian tumors, testicular germ-cell tumors, and lymphoma. The likelihood and type of tumor vary with age, clinical phenotype, antibody association, and other cancer risk factors.[3]
The 2024 Canadian adult consensus recommends initial neoplasm screening without waiting for neural antibody results. CT findings should therefore be interpreted as part of a coordinated tumor investigation, rather than as a substitute for clinical assessment.[4]
Limitations of CT
In autoimmune encephalitis, CT has important limitations:
- Limited sensitivity for brain inflammation: a normal head CT cannot rule out autoimmune encephalitis.
- Incomplete tumor detection: a negative body CT does not exclude an occult neoplasm. CT-based screening has limited sensitivity for some early breast and testicular cancers.
- Patient-specific suitability: radiation exposure and iodinated contrast must be considered. CT is not the preferred screening approach in some groups, including children and pregnant patients; renal impairment or a previous contrast reaction may also alter the plan.[1][3]
Further tumor investigation after a negative CT depends on the clinical and antibody-associated risk. Repeat screening should be individualized, particularly in patients with higher-risk antibodies, refractory or relapsing disease, or other significant cancer risk factors; there is no single repeat-CT schedule appropriate for every patient.[4]
References
- ↑ 1.0 1.1 1.2 1.3 Sanvito F, Pichiecchio A, Paoletti M, et al. Autoimmune encephalitis: what the radiologist needs to know. Neuroradiology. 2024;66(5):653–675. doi:10.1007/s00234-024-03318-x. PMID:38507081.
- ↑ 2.0 2.1 2.2 American College of Radiology. ACR Appropriateness Criteria: Altered Mental Status, Coma, Delirium, and Psychosis. Revised 2024.
- ↑ 3.0 3.1 3.2 3.3 Abboud H, Probasco JC, Irani S, et al. Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management. Journal of Neurology, Neurosurgery & Psychiatry. 2021;92(7):757–768. doi:10.1136/jnnp-2020-325300. PMID:33649022.
- ↑ 4.0 4.1 Hahn C, Budhram A, Alikhani K, et al. Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults. Canadian Journal of Neurological Sciences. 2024;51(6):734–754. doi:10.1017/cjn.2024.16. PMID:38312020.
- ↑ Hellerhoff. Teratom 001-03.png. Wikimedia Commons. January 12, 2011. Original work. Licensed under Creative Commons Attribution–ShareAlike 3.0. Accessed November 5, 2026.