Unmasking the Culprit of Profound Hyponatremia in an Infant.

Infants with severe hyponatremia (Na < 120) and an abdominal mass require an astute clinical evaluation and often represent a medical emergency. We report a case of a 2-month-old White female, born full term, presenting with a two-day history of decreased oral intake and urinary output, who was found to have severe hyponatremia with notable abdominal distention. Abdominal imaging revealed the presence of a pelvic mass causing obstructive uropathy. Further imaging and urogenital examination revealed a hydrometrocolpos. This rare entity required urgent surgical intervention and standard supportive care in the PICU. She had a subsequent significant improvement in symptoms and prevention of further deleterious complications.