Category: Other - Intracranial cyst
Arachnoid cyst (AC) is a rare defect of the central nervous system that accounts for 1% of all intracranial lesions of which only 1% of reported cases are located in the third ventricle. The original defect of the AC can result from a congenital malformation of the neural tube, head trauma, or prior intracranial procedure. Majority of patients with AC are asymptomatic. Endocrine manifestations associated AC include precocious puberty, growth hormone deficiency, and hypothalamic dysfunction. We describe a child who presented with visual field defect, hyponatremia, and precocious puberty related to a third ventricle AC.
Results : A 9-year-old boy presented with decreased vision of the left eye for eight months. He denied any headaches, nausea, or vomiting. His past medical history was unremarkable. Physical examination showed normal vital signs, height was at 90th percentile, and weight at 95th percentile. He had no pubic or axillary hair. His testicles were 3 cm bilaterally (Tanner II) and penile length measured 7.5 cm. Lab tests showed sodium 132 mMol/L, serum osmolality 275 mOsm/kg, urine osmolality 886 mOsm/kg, and testosterone 109 ng/dl. Patient’s bone age was 12 years. MRI brain with contrast demonstrated 5.6x4.1x3.2 cm third ventricle cyst, severe obstructive hydrocephalus, enlarged sella with mass effect on pituitary gland and deviation of pituitary stalk along with findings suggestive for papilledema requiring immediate admission for endoscopic fenestration of the AC. He was diagnosed with SAIDH secondary to third ventricle AC. Prior to surgery, hyponatremia worsened (sodium 129 mMol/L) and he required treatment with 3% hypertonic saline. Adrenal insufficiency was excluded by ACTH stimulation test. Postoperatively, hyponatremia improved (serum sodium 134 mMol/L) with fluid restriction and increased dietary salt intake.
Hyponatremia with AC is not commonly reported. Literature review revealed one case report of SIADH associated with suprasellar AC. The pathophysiology of SIADH in AC is not well understood, but one proposed mechanism suggests that the AC may directly stimulate arginine vasopressin (AVP) neurons in the paraventricular and supraoptic nuclei in the hypothalamus. In addition, hyponatremia may worsen following the endoscopic fenestration of AC secondary to changes in intracranial pressure.
Hyponatremia with AC should be recognized to assist with fluid management especially during the pre- and postoperative periods and may require treatment with hypertonic saline in addition to fluid restriction.
Wayne State University
Second year endocrinology fellow - Wayne State University
Wayne State University
Assistant Professor - Pediatric Endocrinology