A male neonate who had normal anatomy scan at 22 weeks of gestation, born at 35 weeks and 2 days of gestation by spontaneous vaginal delivery. Mum had gestational diabetes which was controlled by diet. Baby delivered in good condition. APGAR score was 9 at one minute and 9 at 5 minutes. His birth weight was 2590 grams. Large 11 cm X 10 cm in size, fluctuant, compressible, nonpainful, well transilluminate lump was detected on left chest wall at birth (Figure 1). Septations within the mass was detected during transillumination (Figure 2). Overlying skin was normal and there was no bruit. Systemic examination of the newborn was normal. There was no dysmorphism.
Figure 1. Cystic, nonpainful, compressible mass on left chest wall.
Figure 2. Transilluminable mass with clearly visible septations.
What is the diagnosis?