Brilliantly transilluminant swellings are all except?

Ans is 'c' i.e. lipoma All the other options except lipoma are cystic lesions containing clear fluid and thus will show brilliant transillumination.Lipoma are not cystic structures but large lipomas are able to show transillumination upto varying extent (though not brilliantly)TransilluminationTransillumination involves shining a light through a swelling to detect whether it transmits light brilliantly or not.It is a function of the optical density of the component elements of the swelling. Light passes easily through clear fluid but not through solid tissues. If a lump trans illuminates then it must contain water, serum, lymph or plasma, or highly refractile fat. Blood and other semi-opaque fluids do not transmit light.Thus a cyst containing clear fluid (e.g. hydrocele, cystic hygroma, meningocele) trans illuminates brilliantly, one containing opalescent fluid (spermatocele) less so. Fat (lipoma) and subcutaneous tissues also transilluminate to a varying extent.