Cranial diabetes insipidus with pituitary stalk lesions.
Cranial diabetes insipidus (CDI) is the deficiency of vasopressin. CDI is rarely resulted from a pituitary stalk lesion; these cases represent a clinical conundrum due to the differing clinical presentations and aetiologies. We present a series of three cases of CDI arising from pituitary stalk lesions/thickenings that highlight both the symptomatic features and multiple aetiologies of this condition.

Vasopressin is an osmoregulatory hormone. It is synthesized in the hypothalamus whereupon it migrates to the posterior pituitary (neurohypophysis). Increased plasma osmolality above 280 mOsmol (milliosmol)/kg is detected by osmoreceptors within the anterior hypothalamus stimulating vasopressin release into the circulation. Vasopressin acts to achieve anti-diuresis through the nephron-mediated conservation of water. In cranial diabetes insipidus (CDI) there is a pathological deficiency in the secretion of vasopressin, resulting in failure to maintain optimal plasma osmolality.1

CDI has a prevalence of fewer than 1 per 25 000 population—up to 25% of these patients have cranial neoplasms or post-pituitary surgery CDI.1 Variant pathologies of the hypothalamus and pituitary including familial disorders such as neurohypophyseal diabetes insipidus and DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness) syndrome result in CDI, which presents clinically with polyuria and polydipsia. CDI rarely occurs secondary to a pituitary stalk lesion.

Anatomically the pituitary stalk, or infundibulum, is the connection between the hypothalamus and the posterior pituitary. The pituitary stalk contains axons, which carry both vasopressin and oxytocin from the hypothalamus to the posterior pituitary. The pituitary stalk measures between 1.9 and 3.5 mm; an increase in size of more than 2–3 mm upon MR imaging is indicative of enlargement secondary to a pituitary stalk lesion or from pituitary stalk thickening.2 Pituitary stalk lesions within adults are typically due to neoplastic conditions of the pituitary such as germinomas or seminomas. Stalk thickening also occurs with inflammatory, autoimmune or infiltrative …