A Large Thyroid Goiter in a Newborn With Congenital Hypothyroidism: Timeline for Decrease in Size of Thyroid.

Congenital hypothyroidism rarely causes a clinically significant neck mass in newborns. We present the case of a newborn with congenital hypothyroidism and significantly enlarged goiter and discuss imaging considerations and medical and surgical management. This infant was prenatally discovered to have a midline neck mass on 28 week ultrasound measuring 6.0 cm × 3.4 cm × 5.8 cm. Diagnostic cordocentesis demonstrated elevated thyroid-stimulating hormone (TSH, 361 µIU/mL). Maternal evaluation for thyroid disease and antithyroid antibodies was negative. A Cesarean section at 38 weeks gestation was recommended due to hyperextension of the fetal neck. The infant was intubated for respiratory distress. Postnatal magnetic resonance imaging revealed a 5.5 cm × 4.4 cm × 7.6 cm goiter and laboratory studies confirmed the diagnosis of primary hypothyroidism (TSH 16.7 µIU/mL). Treatment was initiated with intravenous levothyroxine and transitioned to oral supplementation. Serial ultrasounds showed decreased goiter volume over several weeks, with recent volume per lobe being 22% and 44% of original volume. This case demonstrates the importance of prompt diagnosis and initiation of thyroid hormone replacement, allowing for significant goiter regression without surgical intervention and ensuring normal growth and neurodevelopmental outcome. Surgical management should be considered for those with persistent compressive symptoms despite optimal medical management.