Purpose or Case Report: The purpose of this case report is to alert the reader to a rare differential diagnosis for infra- as well as intradiaphragmatic lung sequestration. A 38-year-old G2P0010 pregnant patient was referred for fetal magnetic resonance imaging (MRI) due to a 14.2 x 20.2 x 18 mm left paraspinal hyperechogenic mass with no internal vascularity and no convincing systemic arterial feeding vessel concerning for neuroblastoma as seen by ultrasound (US) performed at 34 weeks. Fetal MRI performed the same week showed a homogeneous T2-hyperintense left paraspinal mass in close apposition to and associated with a small area of loss of continuity in the diaphragm. This has been previously reported by postnatal computerized tomography as the "split diaphragm" sign in a case of intradiaphragmatic lung sequestration (Meier AH, Eggli KD, Cillei RE. Intradiaphragmatic extralobar sequestration: a rare pulmonary anomaly. Pediatr Surg 200;44:e27-29). Thus, the differential diagnosis provided at the time was congenital intradiaphragmatic sequestration and neuroblastoma. The fetus delivered via uncomplicated spontaneous vaginal delivery at term. Postnatal US performed at the age of 15 days showed a left hyperechogenic mass extending from the left lower chest to the ipsilateral retroperitoneum through a small defect in the diaphragm, favored to represent an extrapulmonary lung sequestration. The left adrenal gland was normal. A follow-up CT performed at 7 months of age showed a 2.6 cm left paraspinal mass with no systemic arterial blood supply to support the diagnosis of sequestration. The differential diagnosis at the time included neurogenic tumor or a myofibroma arising from the diaphragm. Follow-up CT at 13 months of age showed similar findings. The patient underwent uneventful laparoscopic removal of the mass with a final pathological diagnosis of congenital adrenal rest. Congenital adrenal rest presenting as a diaphragmatic mass is rare and as been reported once in an adult patient with an adenoma in heterotopic adrenal tissue located in the left diaphragm, diganosed because of mass effect in the gastric fundus during an uper gastrointestinal series (Keirns MM. Two unusual tumors of the diaphragm. Radiology 1952; 52:542-547). We hope this report raises awareness of this entity as a potential differential diagnosis for prenatal masses seen in close relationship with the adrenal gland and/or diaphragm.
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