Case 833 -- A 4 week-old boy with an abdominal mass

Contributed by Diana Thomas, MD, PhD and Miguel Reyes-M˙gica, MD


The patient is a 4 week-old male infant born at 41 weeks gestation via Cesarean section to a 26 year-old mother who received good prenatal care. Prenatal ultrasounds performed at 20 weeks and 40 weeks gestational age were unremarkable. The delivery was uneventful. On physical exam in the newborn nursery the baby was noted to have right cryptorchidism and a palpable right-sided abdominal mass.


An abdominal ultrasound on postnatal day 4 demonstrated a mass within the right periumbical region with heterogeneous cystic and solid components and confluent areas of calcification resembling a vertebral axis. An abdominal x-ray showed calcifications in the region of the mass seen on ultrasound, suggestive of a teratoma. Subsequent abdominal MRI done at 2 weeks of age showed a large, well-defined encapsulated mass approximately 6.8 x 5.0 X 6.0 cm in size (image 1). A variety of elements were present within the mass including fluid, dense fluid, calcification and fat. Also present was well-organized, randomly distributed bony tissue in the configuration of two separate femora (image 2), as well as evidence of metameric segmentation, represented by a vertical configuration of bone resembling a lumbar vertebral spine (image 3). The mass appeared to be retroperitoneal and was inferior to the right lobe of the liver causing mass effect on the gallbladder and right kidney. There was no evidence of retroperitoneal lymphadenopathy. A follow-up ultrasound of the descended left testis was unremarkable.


Serum levels of the tumor markers AFP and β-HCG were normal for age. Serum estrogen and testosterone levels were also normal.


The patient underwent exploratory laparotomy and excision of the retroperitoneal tumor at 4 weeks of age. The specimen consisted of a red-gray, ovoid, solid and cystic mass weighing 157 grams and measuring 7.5 x 6.0 x 5.5 cm (image 4). The outer surface was smooth and dull with prominent vascularity. A membranous fibrovascular strip with an engorged vein was attached along one aspect. The outer membrane was opened and reflected to reveal cystic cavities containing clear serous fluid and a fetiform mass with rudimentary upper and lower extremities (images 5, 6 and 7). An empty cranial vault was adjacent to the largest lobe of the mass with a recognizable base of skull and presumed foramen magnum (image 8). CT imaging of the mass corroborated the presence of portions of the axial and appendicular skeleton. Sections through the mass showed segments of long bone supported by overlying skin and edematous subcutaneous tissue. Thoracic and abdominal viscera were not seen. An eccentric cystic and solid nodular region measuring 2.0 x 2.0 x 1.0 cm was attached to the mass by a cordlike structure resembling umbilical cord. Gonadal tissue was not seen. A representative portion of skin with subcutis was sent for cytogenetic studies.


Histologic sections showed solid and cystic areas containing multiple tissue elements including: seminiferous cords, epididymis (likely representing remaining testicular parenchyma adjacent to the fetiform mass), bone with trilineage bone marrow, cartilage, intestinal-type mucosa overlying muscle layers containing hypertrophic nerve trunks and ganglion cells, skin with adnexal structures, mature and immature adipose tissue, skeletal muscle, and adrenal cortex (images 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 and 19). Structures reminiscent of embryonal lung were also present. No immature germ cell components were identified.


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