Exploring immunoreactivity of TTF-1 and AVP in hypothalamic hamartoma

Hypothalamic hamartoma (HH) is a rare developmental disorder presenting with gelastic seizures or precocious puberty attributed to gonadotrophin-releasing hormone expression by the hamartoma. The histogenesis of HH is uncertain, and diagnosis of HH is difficult in small biopsies due to its close resemblance to normal hypothalamic nuclei. TTF-1 and arginine vasopressin (AVP) are associated with gonadotropin-releasing hormone release.

In this study, we explored the expression pattern of TTF-1 and AVP in HH and its utility, if any, in diagnosis. We reviewed the clinical, radiologic, and histopathological features of 23 HH diagnosed over the past decade at our Institute.

The age at presentation ranged from 11 months to 34 years with gelastic seizures (82.6%), precocious puberty (17.4%), and developmental delay (8.7%) as presenting symptoms. On imaging, all the lesions (n = 9) involved the posterior and tuberal group of hypothalamic nuclei, while 5 cases involved the anterior hypothalamus. Anatomically, the lesions involved mammillary body, arcuate and periventricular nuclei. On histopathology, 52% cases revealed nodular arrangement of small neurocytic cells separated by glial stroma. TTF-1 and AVP immunoreactivity was absent in all the cases, whereas in normal hypothalamus, AVP was expressed in periventricular nuclei.

Our results suggest that immunoexpression of TTF-1 is absent in HH, particularly in those arising from the posterior hypothalamus, and this can be used in small biopsies to distinguish from a normal hypothalamus as well as from posterior pituitary tumors.