• Most commonly encountered abnormalitieson neuroimaging.• These lesions appear as hypodense orisodense mass lesions on non-contrastcomputed (plain) tomography studies.
• After contrast administration, there is a ring-or a homogeneous disk-like enhancementwithin the region of hypodensity. Theenhancing lesions are often of variable sizeand are usually surrounded by a varyingamount of perifocal vasogenic edema.
• Typically, the ring-enhancing lesions arelocated at the junction of the gray and whitematter, but they could be located in the sub-cortical area, deep in the brain parenchyma ormay even be superficial.
Contrast-enhanced computed tomographyshowing two enhancing lesions•
• Clinically, they manifest as recurrentseizures, visual impairment, focal neurologicaldeficit and raised intracranial pressure (severeheadache, vomiting and papilledema).
• If cerebral edema is severe, patients maydevelop loss of sensorium and posturing oflimbs because of transtentorial brainherniation. Intractable headache, focalneurological deficits and vision loss are long-term sequelae in few of the surviving patients.
ETIOLOGY• Causes of multiple ring-enhancing lesions ofthe brain
Figa)Contrast-enhanced magnetic resonanceimaging showing multiple enhancing lesionsof variable sizes;b)X-ray chest of the same patient showing acannon ball shadow and diffusecarcinomatous lung infiltration
• Metastatic lesions are typically subcortical,occurring in or near the gray matter-white matterjunction, and are usually associated with severeperilesional edema.• Primary brain tumors frequently cross themidline. For example, glioblastoma multiformefrequently crosses the midline by infiltrating thewhite matter tracts of the corpus callosum.
Pyogenic Brain Abscesses• Multiple brain abscesses are often caused byhematogenous spread of bacteria from aprimary source and are frequently found inthe territory of the middle cerebral artery.
• The enhancing ring lesions caused by pyogenicbrain abscesses are commonly located at thegray-white matter junction.• The capsule of abscess is difficult to visualizevia conventional imaging techniques anddouble-contrast computed tomography isneeded to clearly define the capsule of theabscess.
• However, greater thickness, irregularity andnodularity of the wall of the lesions are oftensuggestive of tumor or a fungal infection.
• TuberculomaTuberculomas are frequently encounteredbrain lesions in tropical countries.• Intracranial tuberculoma can occur with orwithout tuberculous meningitis.• Numerous small tuberculomas are commonin patients with miliary pulmonarytuberculosis.
• A non-caseating tuberculoma usually appearshyperintense on T2-weighted and slightlyhypointense on T1-weighted images.• A caseating tuberculoma appears iso- tohypointense on both T1-weighted and T2-weighted images, with an iso- to hyperintenserim on T2-weighted images.
• Tuberculomas on contrast administrationappear as nodular or ring-like enhancinglesions.• The diameter of these enhancing lesionsusually ranges from 1 mm to 5 cm.• Tuberculomas frequently show varied types ofenhancement, including irregular shapes, ring-like shapes, open rings and lobular patterns.Target-like lesions are common.
Contrast-enhanced magnetic resonance imaging showingmultiple enhancing lesions and X-ray chest of the same patientshowing miliary pulmonary tuberculosis
• Cysticercus GranulomaNeurocysticercosis - most common parasiticdisease of the CNS and is a major cause ofseizures worldwide.• After reaching inside the brain parenchyma,the cysticercus larva passes through severalstages of evolution
• . Initially, the cyst consists of a protoscolexsurrounded by a bladder wall. This stage ofviable cyst is known as vesicular cyst stage.• At this stage, the scolex usually is identified asan eccentric nodule within the cyst.
• colloid cyst stage- the cyst wall gets thickenedand hyaline degeneration and mineralizationof the cyst take place. The cyst fluid becomesopaque . These degenerating cysts are calledcolloid cyst stage• In this stage, there is an intense inflammatoryreaction in the surrounding brain tissue.
• In this stage, neuroimaging reveals contrastenhancing ring or disc lesions.• Granular nodular stage- the cysticercus is nolonger viable & the bladder wall collapses toform a small granuloma.• Calcific stage. Months to years later, some ofthese dead cysts get calcified into smallnodules. This stage is called calcific stage.
• Cysticercus granuloma shows a ring pattern ofenhancement after contrast mediumadministration.• Usually, the lesions are <20 mm in diameter.• Calcified eccentric scolex is often seen in acysticercal lesion.• The lesions are often multiple and most oftendo not have extensive edema.
• Demyelinating DisordersDemyelinating lesions, including both classicmultiple sclerosis and tumefactivedemyelination, may also create an open ringor incomplete ring sign.
• Multiple Enhancing Lesions in HIV-infectedPatientscategories –1 opportunistic infections,2 neoplasms and3 cerebrovascular diseases.The common causes include toxoplasmosis,tuberculoma and primary CNS lymphoma and,rarely, brain abscess and fungal granuloma.
• The lesions of primary CNS lymphoma oncomputed tomography are hyperintense orisointense with homogeneous contrastenhancement and variable surroundingedema.• They are often multifocal and periventricularin location. Leptomeningeal involvement maybe seen.
• Lymphomatous lesions are frequentlyperiventricular and have indistinct borders.• The lymphomas rarely invade the basalganglia and have a tendency to occur in thewhite matter adjacent to an ependymalsurface.
• Methods used for establishing thediagnosis in patients with multipleenhancing lesions of the brain
• Differential diagnosis of multiple ring-enhancing lesions of the brain