Purpose or Case Report: A previously healthy 12 year old female presented with left lower back pain and left thigh numbness. MRI showed a T1 isointense, heterogeneously T2 hyperintense left retroperitoneal mass with extension into the paraspinal muscles and intraspinal extension through the L1-L4 neural foramina. CT and contrast enhanced MRI (CE-MRI) of the lumbar spine and I-123 MIBG scintigraphy were performed. CT did not show any calcifications. MRI showed mildly heterogeneous, avid gadolinium enhancement. The mass was I-123 MIBG avid, without evidence of metastatic disease. Ultrasound guided biopsy yielded ganglion cells and no neuroblasts, suggestive of ganglioneuroma (GN). Partial excision of the retroperitoneal component yielded a 7 x 6 x 3 cm aggregate of tissue, and histopathology confirmed GN.

Follow up CE- MRI at 4, 10, and 16 months after surgery showed stable residual mass. CE-MRI at post op month 23 showed numerous T2 hyperintense enhancing osseous masses in the lumbar spine and sacrum. Residual mass remained stable. A fluoroscopically guided biopsy of a right sacral lesion yielded neuroblastoma. Review of the pathology from the original excision confirmed GN. Whole body I-123 MIBG scintigraphy showed the avid mass and confirmed skeletal metastases.

Ganglioneuromas (GN) are benign tumors of neural origin that exist on a spectrum with ganglioneuroblastoma (GNB) and the frankly malignant neuroblastoma (NB). CT, MR, and nuclear scintigraphy are unreliable for the differentiation of NB/GNB from GN. The most robust imaging feature to identify NB is the presence of distant metastases. Imaging findings that have been proposed as possible distinguishing features are the morphology of the calcifications, early versus delayed gadolinium enhancement, and ADC values. It is a well-known phenomenon that NB may regress into GNB or GN either spontaneously or following treatment with chemotherapy and/or radiation. To our knowledge, only one other case of GN de-differentiating into NB has been reported. Due to the extreme rarity of this case, alternatives must be considered. It is possible that the patient had a bi-phenotypic tumor and the NB component was not sampled initially or that she developed a NB extrinsic to the GN. These alternatives seem unlikely since NB is a rare tumor in 12 year olds, the residual tumor did not change on follow-up imaging, no new primary tumor was seen on recent MIBG, and two years passed prior to the development of metastasis.
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