Aggressive eosinophilic granuloma of the parietal bone. An immunohystochemical study of Ki-67 expression.

Solitary eosinophilic granuloma (EG) of the skull is a rare lesion, the natural history of which is still to be defined. We report a case of a 26-year-old female who presented with progressive headache and nausea accompanied by a painful firm mass in her left parietal region, which grew very rapidly during the last two weeks before admission. Computed tomography scan showed an osteolytic lesion, which on magnetic resonance imaging appeared hyperintense on both T1- and T2-weighted images, with marked and heterogeneous enhancement after gadolinium administration. Total surgical excision of the lesion was performed and histopathological diagnosis was compatible with eosinophilic granuloma. Immuno-histochemical study of Ki-67 antigen expression was also performed with a labelling index of 10%. In a review of the pertinent literature, we found one case report showing a Ki-67 labelling index of 6.2% in a patient harboring EG of the occipital bone. These two relatively high percentages of proliferative activity suggest a role of local Langerhans'cell proliferation, along with that of inflammatory response, in the aggressive clinical course and rapid expansion observed in some rare cases of solitary eosinophilic granuloma.