Infundibulo-neurohypophysitis in a pediatric patient

A 4-year-old girl with intermittent headache, polydipsia, polyuria and nocturia of very dilute and hypotonic urine in the past 4 weeks. No relevant personal or family history. She was admitted to the pediatric unit for further examination. MRI of the brain was performed.

Brain MR Imaging revealed enlargement of the posterior lobe of pituitary gland and infundibulum, loss of T1 posterior pituitary bright spot (Figure 1) and pituitary infundibulum stalk thickening (4,2 mm) (Figures 2 and 3). Adenohypophysis was anteriorly displaced, but it was normal in size. Post-gadolinium enhacement MRI showed infundibulum and neurohypophysis were relatively hypoenhancing relative to the adenohypophysis. Sella floor was intact, not expanded or eroded.

Background

Hypophysitis is a rare neurological condition, characterized by inflammation of the pituitary gland that can also affect the infundibulum [1]. It can be classified into primary causes, including lymphocytic, granulomatous, xanthomatous, and necrotizing, and secondary causes resulting from systemic inflammation [2].

Lymphocytic hypophysitis is an uncommon autoimmune inflammatory disorder [1,3].  Most affected patients are women; however, there are reported cases of men [4]. Two forms have been described; the first process is lymphocytic adenohypophytis, which occurs mainly during pregnancy and the postpartum period [5]. It is by far the most common type of lymphocytic hypophysitis. The second process is lymphocytic infundibulo-neurohypophysitis (LINH) that selectively affects the posterior lobe of the pituitary gland and the infundibulum, as the patient we present here. Although most affected patients are also women, it is not clearly associated with the postpartum period [3]. LINH is a very rare condition, especially in children, and the differential diagnosis should include psychogenic polydipsia [6].

Clinical Perspective

LINH produces an antidiuretic hormone deficiency which causes polydipsia and polyuria of very dilute and hypotonic urine (central diabetes insipidus), with persistent excretion of hypotonic urine and an increase of plasma osmolality during the water deprivation test [7]. Other less frequent symptoms are headache, and other hormonal deficiencies that induce adrenal insufficiency, hyperprolactinemia, and hypogonadism [2].

Imaging Perspective

LINH selectively affects the posterior lobe of the pituitary and the pituitary stalk. MRI brain findings include isolated enlargement of the posterior lobe of the pituitary gland, thickening of the infundibular stalk (greater than 4 mm) and absence of the T1 pituitary bright spot [1]. Adenohypophysis is normal in size. Pituitary gland presents variable enhancement.

Neurohypophysis secretes two hormones that are stored as secretory granules in the axon terminals of the posterior lobe of the pituitary gland: oxytocin and antidiuretic hormone (also called vasopressin). The T1 pituitary bright spot reflects the normal hormones storage in the neurohypophysis, its absence denote a lack of antidiuretic hormone, the cause of central diabetes insipidus [3].

Treatment and Outcome

Neurohypophysis enlargement and infundibular stalk thickening can reduce or resolve in MRI brain controls [3]. Nevertheless in most cases diabetes insipidus is usually permanent, for this reason desmopressin acetate becomes a chronic treatment.

Our pacient was treated with desmopressin acetate with total regression of symptoms. Nowadays she remains asymptomatic with antidiuretic hormone replacement.

Written informed patient consent for publication has been obtained.