SUN-458 Use of Positron Emission Tomography in Pituitary Adenomas in Uruguay: a Case Series

Abstract

Imaging of tumor biology can be useful for pituitary adenomas (PA). Positron emission tomography (PET) with 11C-methionine (MET) can reveal aminoacid (AA) uptake and protein synthesis whereas 11C-raclopride evaluates dopamine D2 receptors (D2) in prolactinomas (PRL), non-functioning PA (NFA) and GH secreting PA (ACR). 18F-Fallypride (FP) is a molecular tracer of D2. We present 7 patients with PA that were evaluated with PET. Case 1: A 64 year-old male with a PRL (prolactin (PL) of 1477 ng/ml) and a 15X15X18 mm-cystic tumor on MRI. Cabergoline (CB) up to 3.5 mg/week was done, with no changes in tumor size. FP-PET showed low expression of D2 and 11C-Methionine-PET (MET-PET) showed low AA uptake. Case 2: A 42 year-old male with initial PL levels of 280 ng/ml and a 27x30x30 mm-hemorrhagic PRL on MRI. Treated with CB up to 10 mg/week due to failure to normalize PL. MRI showed a significant reduction in tumor size (9 mm). FP-PET revealed adequate expression of D2 and MET-PET showed moderate AA uptake at the right side of the tumor. Case 3: 27 year-old female, with PL of 470 ng/ml and a 34 mm solid-cystic PRL on MRI. CB was started up to 9 mg/week due to failure to normalize PL, but with a significant reduction of tumor size (6mm). MET-PET did not show uptake, and FP-PET revealed a moderate expression of D2. Case 4: 63 year-old female, diagnosed with a 44x25mm NFA. She had 2 transsphenoidal surgeries (TSS) and posterior radiotherapy, but tumor grew in FU. MET-PET showed high uptake in the PA and FP-PET revealed adequate expression of D2. CB was indicated till 2 mg/week. Case 5: 53 year-old male was diagnosed with ACR with a tumor size of 24x24x30 mm and underwent a TSS. He was treated with octreotide and CB till 3.5 mg/week without IGF-1 normalization. MET-PET revealed mild uptake at site of pituitary tumor, with a higher uptake at its right side. Case 6 and 7: We describe two 59 and 55 year-old females, who were diagnosed with Cushing’s disease (CD), with <6 mm lesions on MRI. MET- PET did not reveal uptake in one of the cases and an upper normal uptake at the pituitary gland in the other. Discussion: PRL with significant tumor reduction showed adequate expression of D2, while the case without changes in size disclosed low expression of D2. The PRL that had D2 expression and significant tumor size reduction did not show uptake with MET, but a decreased uptake has been reported after DA. In NFA we found an adequate expression of D2. Some of those reported to have D2 responded to DA. In ACR, MET-PET was reported to be helpful to identify residual PA and facilitate further treatment. In our case, it showed a localized site of abnormal tracer uptake. In CD, MET-PET was reported to successfully localize microadenomas, but in our cases it failed to identify tumor. In conclusion, metabolic imaging may be a useful tool for PA. It may help in the diagnosis, identify recurrence and monitor response to therapy. Additional studies are warranted to further evaluate its utility.