Light bulb sign refers to the persistent T2 bright homogeneous signal intensity of a typical liver hemangioma, on increasing the TE (T2 weightage) of the image. The bright signal is compared to that of a glowing light bulb. This may however also be seen in hypervascular metastases.
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MRI Liver of an young patient with multiple hemangiomas in both lobes.
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On increasing the TE, the signal intensity of hemangioma is well preserved, whereas the signals of other structures such as liver and spleen gets reduced.
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Hemangiomas are T2 homogenously hyperintense, with well defined margins with or without small lobulatations. They appear hypointense in T1WI, hyperintense in DWI. In post Gadolinium images they show peripheral nodular intense enhancement in the arterial phase, with gradual centripetal filling-in of the contrast. In the delayed hepatobiliary phase hemangiomas appear hypointense as they do not contain any hepatocytes.
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