J. Oh

SUMMARY: Idiopathic hypereosinophilic syndrome (HES) is a heterogeneous disorder characterized by prolonged eosinophilia without an identifiable cause, ultimately resulting in organ dysfunction. Three major types of neurologic involvement have been well defined in HES; however, to our knowledge, inflammatory pseudotumor (IPT) in association with HES has not been reported. We present a case of IPT of the skull base in a patient with HES that suggests that HES may result in an exaggerated immunologic or inflammatory response leading to the formation of IPT. Idiopathic hypereosinophilic syndrome (HES) was first de-fined by Chusid et al in 19751 as unexplained eosinophilia of greater than 1500/L present for longer than 6 months with evidence of organ injury related to the hypereosinophilia, such as cardiomyopathy, peripheral neuropathy, and encephalop-athy. The heterogeneity of HES ranges from those patients with myeloproliferative features (splenomegaly, increased vi-tamin B12 levels, abnormal leukocyte alkaline phosphatase scores, and cytogenetic abnormalities) to those patients with benign courses (associated with increases in immunoglobuli