Imaging technique nearly matches MRI in detecting Cushing’s tumors
Study: PET-based scan 'may have added value in certain challenging cases'
A positron emission tomography (PET)-based imaging technique is comparable to standard MRI in its ability to find small pituitary gland tumors related to Cushing’s disease, a study reports.
While both techniques correctly identified the location of the tumors, called small pituitary neuroendocrine tumors (PitNETs), for most study participants, neither was able to do so in a subset of cases.
Still, the PET-based technique, called [11C]methionine ([11C]MET) PET/MRI, “may have added value in certain challenging cases,” researchers wrote.
The study, “Prospective Multicenter Evaluation of [11C]Methionine PET/MRI Sensitivity Compared with MRI for Localizing Small Pituitary Neuroendocrine Tumor or Pituitary Adenoma in Cushing Disease,” was published in the Journal of Nuclear Medicine.
Cushing’s treatment often involves surgery to remove pituitary tumors
Cushing’s disease, marked by elevated levels of the hormone cortisol, is caused by PitNETs arising from corticotroph cells, a type of cell in the brain’s pituitary gland that produces adrenocorticotropic hormone (ACTH). This hormone signals to the adrenal glands located atop the kidneys to produce cortisol.
Although corticotroph-type PitNETs aren’t cancerous, they increase the production of ACTH, which subsequently leads to an increase in cortisol levels and associated symptoms such as weight gain and emotional disturbances.
Treatment for Cushing’s often involves removing these pituitary tumors through surgery. Clinicians typically will attempt to identify and locate the tumor before this procedure. This includes identifying if the PitNET is on the left or right side of the pituitary, or if it is in the middle (median) part.
“Pituitary MRI is the primary imaging modality used to localize the tumor, but it is inconclusive in up to 30% of cases,” the researchers wrote.
As such, there is interest in developing more sensitive techniques. One strategy is to use a combination of PET and MRI.
PET scans involve injecting a radioactive tracer into the bloodstream and identifying the locations in the body where the tracer accumulates. These are possible locations of tumors or other diseases.
MRI, PET-based scan agree on tumor location in most cases
In this study, a team of researchers in France conducted a clinical study (NCT03346954) to compare PitNET localization performance of standard MRI scans to [11C]MET PET/MRI scans, which use a specific tracer called [11C]MET for the PET scan.
Five clinical centers in France recruited 33 adults with newly arising Cushing’s. Of these, 30 completed the PET scans. The mean age of these participants was 39.4, and most (73%) were women.
Participants underwent surgery to remove the tumor at a median of 21 days after PET/MRI scans. Tumor samples examined on the microscope confirmed a corticotroph-type PitNET in 22 people (73%).
“The absence of [tissue-based] confirmation in 8 patients underscores the inherent challenges in definitively localizing corticotroph-type small PitNETs,” the researchers wrote.
Analysis of the relative performance of the two imaging techniques focused on individuals with a confirmed corticotroph-type PitNET. Among these participants, MRI correctly identified if the tumor was left, median, or right in 86% of cases. Similarly, [11C]MET PET/MRI accurately localized the PitNET in 82% of cases.
Out of the 18 cases where the two imaging methods agreed on tumor location, all but one were accurate.
Of the four cases where the methods disagreed, MRI correctly localized the tumor in two cases where [11C]MET PET/MRI was inaccurate. The PET scan correctly identified the tumor in one case where MRI failed, and both techniques failed to locate the tumor in the remaining case. All four cases were ultimately classified as being in remission.
Other imaging techniques should be explored, researchers say
Participant demographics were broadly similar for cases in which [11C]MET PET/MRI identified the correct location and cases in which it didn’t. There were also no significant differences in tumor size, blood ACTH levels, or medication use between the two groups.
“The findings herein, which are more robust due to the larger sample size and prospective design, suggest that [11C]MET PET/MRI may provide additional value compared with MRI alone for the accurate localization of small PitNETs in [newly-developed Cushing’s disease],” the researchers wrote.
Still, “the added value of PET/MRI in cases of negative MRI could not be clearly evaluated herein, because most patients had a correctly localized lesion on MRI (19/22 patients),” they added.
Despite the generally good performance of MRI, the scans couldn’t correctly identify tumor location in 14% of cases. Other techniques, including different types of PET scans, might improve this rate.
“Future research should focus on exploring alternative [radioactive tracers] and could potentially benefit from emerging imaging technologies,” the researchers wrote.
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