Background: Neurofibromatosis type 1 is a rare, autosomal dominant genetic disorder caused by mutations in the NFx1 gene, which codes for neurofibromin. The loss of neurofibromin predisposes NF1 individuals to neurofibromas, such as plexiform neurofibromas. The malignant transformation of plexiform neurofibromas to peripheral nerve sheath tumors has been shown to have worse outcomes. Currently, MRI and FDG-PET scans are used to detect tumors in NF1 patients. However, detecting malignant transformation of NF1-associated plexiform neurofibromas utilizing Gallium Dotatate 68, a radiopharmaceutical agent, has not been reported in the current English literature. We present the first reported case of detecting transformation of NF1-associated neurofibroma to malignant peripheral nerve sheath tumor (MPNST) through the utilization of Gallium Dotatate 68.

Case: A 13-year-old male with a history of neurofibromatosis type 1 mutation, confirmed with a truncating mutation (c.8134_8135delAA) in Neurofibromin by genetic testing, was referred to the ENT (ears, nose throat) service for a complicated right retropharyngeal mass causing obstructive sleep apnea. The initial evaluation for sleep apnea by the ENT service showed a large right retropharyngeal mass. Initial follow-up imaging with a Neck MRI scan showed a lobular, well-circumscribed mass centered within the right retropharyngeal space with lateral extension into the carotid space. Subsequent Gallium 68 Dotatate PET/CT scan showed a markedly abnormal tracer uptake in the right retropharyngeal mass with a mild uptake in the right parotid gland, greater than the left. The two scans raised suspicion for malignant transformation of a large neurofibroma in the right retropharynx. The patient underwent ultrasound-guided core needle biopsy of the right retropharyngeal mass. The biopsy confirmed malignant transformation of a benign neurofibroma to malignant peripheral nerve sheath tumor (MPNST). Following the diagnosis of MPNST, the patient underwent oncologic management with chemotherapy and radiation to reduce tumor size prior to resection. Subsequently, the patient was cancer-free for more than two years. Recently, the patient developed multifocal pulmonary and hepatic metastatic disease on follow-up imaging that was confirmed via lung biopsy. The patient is currently undergoing treatment with additional chemotherapy and radiation for recurrent disease.

Discussion: The Gallium 68 Dotatate PET/CT scan helped to confirm the MRI scan findings and suggested a new, important finding: metastasis to the right parotid gland. This case report demonstrates that Ga-68 Dotatate PET scans can be utilized as an effective alternative for early detection, diagnosis, and metastasis for MPNSTs in NF1 patients. Additional research into the use of Ga-68 Dotatate PET scan in detecting MPNSTs is necessary to determine the sensitivity and specificity of this pharmaceutical agent compared with the standard F18- FDG PET scan. Other future research prospects are the role of Ga-68 Dotatate in treatment and in follow-up imaging of MPNSTs in NF1 patients.