Pandora's box: eosinophilic granuloma at the cerebellopontine angle-should we open it?

Langerhans cell histiocytosis (LCH) is a disorder of immature LCH cells, eosinophils, macrophages, lymphocytes, and multinucleated giant cells. Eosinophilic granuloma (EG) is a focal form of LCH that presents mostly in the skull, femur, vertebrae, pelvis, mandible, and ribs. Intracranial presentation of EG is very rare in the literature. A 17-year-old boy visited our clinic with headache, dizziness, and tinnitus that were present for 2 months. Brain MRI depicted a lesion at the right cerebellopontine angle. The lesion was hypointense on T1-weighted and hyperintense on T2-weighted brain MR images. The lesion enhanced homogenously after I.V. contrast material administration. Pre-operative diagnoses were vestibular schwannoma and meningioma. Surgery was planned. Retrosigmoid approach was preferred in the surgery. The lesion was excised partially. Pathological analysis depicted cell infiltration composed of eosinophils besides histiocytes, plasma cells, and lymphocytes in different amounts. CD1a was positive yet S100 was negative. Final diagnosis was eosinophilic granuloma. Post-operative course was uneventful. The patient was referred to pediatric oncology unit, and steroid therapy was initiated. Post-operative follow-up brain MRIs showed that the lesion had regressed further than immediate post-operative images by only steroid use. In long-term follow-up, new lesions appeared on the patient's skin in multiple locations and in the sclera of his left eye. At the last follow-up (3 years post-operatively) skin and scleral lesions were noticed to have regressed spontaneously and the intracranial structures were tumor free. To the best of our knowledge, EG at the cerebellopontine angle has not been presented in the literature. What makes our case further unique is its negativity for S-100 antigen. Eosinophilic granuloma should be kept in differential diagnosis of mass lesions presented at the cerebellopontine angle, especially in children and young adults with high eosinophils and lymphocytes in their peripheral blood. Sole steroid trials could be conveyed in suspicious cases before any further intervention. If the lesions do not regress or enlarge with time, surgery should be considered. However, long-term follow-up of these patients is necessary since natural history of the disease has not been defined, yet.