# Unmasking the Culprit of Profound Hyponatremia in an Infant

## TL;DR

A 2-month-old infant with severe low sodium and an abdominal mass was diagnosed with a rare condition requiring urgent surgery.

## Contribution

This case highlights hydrometrocolpos as a rare cause of profound hyponatremia in infants requiring emergency surgical intervention.

## Key findings

- Severe hyponatremia in an infant was linked to a pelvic mass causing obstructive uropathy.
- Hydrometrocolpos was identified as the underlying cause requiring urgent surgical treatment.
- The infant showed significant improvement after intervention and supportive care.

## Abstract

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.