Meningeal Lipomas in the Foramen Magnum.

LIPoMAs rarely develop in the meninges. Within the skull the favourite site of the lipomas is the dorsal surface of the corpus callosum; the region of the tuber cinereum and the midbrain seem to be frequent sites, although much less so than the corpus callosum. Sometimes they are associated with malformations of the brain, especially with defects of the corpus callosum. Most of the lipomas in the skull do not cause symptoms and are found incidentally at necropsy (Bailey). About their origin there are many theories: (a) that they arise from lipoid cells already present in the pia mater; (b) that they arise by fatty transformation of the connective tissue; (c) that they arise by differentiation of the pial cells towards an embryonic form, with a subsequent metaplasia into fat; (d) that they arise from embryonal remnants (Verga). The last lists of lipomas found in the central nervous system are in the papers of v. Sury and of Verga, which is a kind of monograph on the lipomas of the pia mater. Large lipomas at the base of the brain with distinct symptoms and signs have been described (Hirtz, Klob, Shaw). But most of these tumours did not cause any symptoms, even when they were situated near the foramen magnum. Only a few lipomas have been described in this area; and their clinical picture has been ignored or the description has been brief. The first was described by Cruveilhier (1856, quoted by Bostroem and others) on the left side of the medulla in the olive beneath the arachnoid; although it was of the size of a pea it did not produce any symptoms. In a case of Leyden (a female, aged 28 years) a lipoma on the foramen magnum, bulging towards the pons and medulla, caused symptoms of vertigo, hemiparesis of the left side with pains in the left limbs, disturbances of speech and swallowing; in this case the right sixth and tenth nerves were found atrophied and the medulla softened. The other few cases described in this region were either enchondromata (Bostroem, Balz) or not well-defined tumours (Gowers, Watzoldt). The two lipomas of the foramen magnum to be reported here * seem to be the first ones with a long-standing history and with repeated clinical