1. Abstract Id: IRIA - 1052

2. Introduction Among the widely used neuro imaging techniques ie computed topography and MRI, numerous etiologies may present as ring enhancing lesions. On non contrast images these lesions usually appear as hypodense or isodense. However on post contrast, there is a homogeneous disk like enhancement within the region of hypodensity and is usually associated vasogenic oedema.

3. Causes BACTERIAL- - Pyogenic abscess - Tuberculoma - Syphilis - Listeriosis Contd.. Ring enhancement Pyogenic Abscess

4. PARASITIC- - Neurocysticercosis - Toxoplasmosis - Amoebic brain abscess - Echinococcus - Cerebral sparganosis Contd.. Neurocysticercosis

5. NEOPLASTIC - Metastasis - Primary brain tumour - Primary CNS lymphoma Contd.. Metastasis

6. FUNGAL- - Cryptococcosis - Actinomycosis - Aspergillosis - Histoplasmosis - Nocardiosis - Zygomycosis INFLAMMATORY AND DEMYELINATING - Multiple sclerosis - Acute disseminated encephalomyelitis - Sarcoidosis - Neuro Behects disease - Systemic lupus erythematosus

7. Radiographic features Enhancing wall characteristics - Thick and nodular is in favour of neoplasm - Thin and smooth favours abscess - Incomplete ring opened towards cortex favours demyelination - Intermediate to low T2 signal capsule favours abscess - Restricted diffusion of enhancing wall favours GBM or demyelination. Contd..

8. Surrounding oedema - Extensive oedema relative to lesion size favours abscess - Increased perfusion favours neoplasm Central fluid/ content - Restricted diffusion favours abscess Number of lesions - Similar sized rounded lesions at grey white matter favours metastasis/ abscess - Irregular mass with adjacent secondary lesions embedded in the region of oedema favours GBM - Small (< 1-2 cm) lesions with thin walls and calcifications are in favour of neurocysticercosis

9. Neoplasm The imaging features of both primary and metastatic tumors usually manifest as rounded, well-circumscribed, ring enhancing lesions of variable sizes surrounded by a variable amount of vasogenic oedema. MRI reveals mild T1 hypointensity with T2 hyperintensity and fluid-attenuated inversion recovery hyperintensity at the site of lesion. T1WT1W- ContrastT2W FLAIRT2W

10. Pyogenic abscess The lesions are commonly located at the gray-white matter junction. Non contrast MRI shows an isointense to slightly hyperintense capsule on T1 weighted images, and is hypointense on T2 weighted images. The ring enhancement on post-contrast images is usually thin and smooth and often thinner along the medial margin. T1WT2WT2W FLAIRT1W- Contrast

11. Tuberculomas Non caseating tuberculoma usually appear hyperintense on T2 weighted images and slightly hypointense on T1 weighted images, however caseating tuberculoma appear iso to hypointense on both T1 weighted and T2 weighted images, with an iso to hyperintense rim on T2 weighted images. On contrast study it appears as nodular or ring-like enhancing lesions. The diameter of these enhancing lesions usually ranges from 1 mm to 5 cm. Tuberculomas frequently show varied types of enhancement, including irregular shapes, ring-like shapes, open rings and lobular patterns. T1WT2WT2W FLAIRT1W- Contrast

12. Neurocysticercosis On MRI, the wall of the cysticercus granuloma (a colloid cyst stage) becomes thick and hypointense and there is marked perilesional edema on T2 weighted images. Cysticercus granuloma shows a ring pattern of enhancement after contrast medium administration. Usually, the lesions are <20 mm in diameter. Calcified eccentric scolex is also often seen. The lesions are often multiple and most often do not have peri lesional oedema. T1WT2WT2W FLAIRT1W- Contrast

13. Subacute Infarct T1WT2W T2W FLAIR T1W- CONTRAST DWIADC

14. Demyelinating disorders Multiple enhancing ring lesions may be encountered. Enhancing demyelinating lesions differ in size, shape or pattern, most demonstrating a nodular pattern whereas some demonstrate a ring enhancing pattern while few have other patterns. Presence of an open ring or incomplete ring lesion is also characteristic in differentiating demyelinating lesions from large brain tumors or infective lesions like brain abscess. T1WT2WT2W FLAIRT2W- Contrast

15. Glioblastoma multiforme Glioblastoma multiforme usually appear as hypo to isointense mass within white matter with a central heterogenous signal on T1 weighted images. On contrast its enhancement is variable showing a peripheral and irregular pattern with nodular components. On T2 / FLAIR it appears hyperintense surrounded by vasogenic oedema with occasional flow voids. There is a low intensity rim from blood product which is incomplete and irregular in 85% when present and is mostly located inside the peripheral enhancing component. There is no diffusion restriction, however, lower measured ADC than low grade gliomas T1WT2WT2W FLAIRT1W- Contrast

16. CNS Lymphoma It is typically hypointense to white matter on T1 weighted images. On contrast study it shows strong homogenous enhancement for high grade tumours while low grade tumours have absent to moderate enhancement. T2 weighted images show iso to hypo intensity. Isointense 33%, hypointense 20% and hyperintense 15-47% which are more common in tumours with necrosis. DWI shows typical restricted diffusion. T1WT2WT2W FLAIRDWIT1W- Contrast

17. Conclusion Ring enhancing lesions caused by common non- neoplastic and neoplastic disorders remain a diagnostic challenge inspite of clinical evaluation and a battery of tests. In a majority of such cases, biopsy of the lesion(s) remain the only option to establish a confirmative diagnosis.

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