Congenital cutaneous paraspinal müllerian choristoma in a boy: A case report

I. Abstract Introduction Müllerian choristomas are developmental lesions composed of histologically normal Müllerian-type tissue in an ectopic location. Reported spinal and paraspinal examples are exceptionally rare and have almost invariably been described in female patients with spinal dysraphism or a lipomatous malformation. Case presentation A 3-year-old boy was evaluated for a congenital 2-cm pedunculated reddish right lumbar paraspinal lesion with an underlying soft subcutaneous prominence. It had enlarged only in proportion to the child's growth, and neurological examination was normal. External genitalia were normally male, both testes were scrotal, and there was no known difference of sex development. Neonatal spinal ultrasonography had shown a normally positioned conus, normal cord and filum terminale, and no spinal dysraphism, tract, meningocele, or intraspinal or extraspinal lipoma. Abdominopelvic ultrasonography was normal, with no internal Müllerian structure identified. The lesion was surgically excised in May 2026. Histological examination showed a polypoid lesion containing smooth muscle bundles, thick-walled vessels, peripheral nerves, and nonciliated endometrioid-type glands. The glands expressed PAX8 and were surrounded by CD10-positive and estrogen receptor-positive endometrial-type stroma, supporting Müllerian differentiation. Resection margins were free. Recovery was uncomplicated, and the child was well with a normal scar at the 5-week review. Conclusion Müllerian choristoma must be included in the differential diagnosis of congenital cutaneous paraspinal lesions, and spinal dysraphisms should be ruled out in children with confirmed cutaneous Müllerian choristomas.