New imaging technique found to accurately ID pituitary tumors
Novel method may aid clinicians in diagnosing difficult cases: Study
An imaging technique developed by scientists in India may help clinicians accurately identify tumors associated with Cushing’s disease, including in cases that are difficult to diagnose with other methods, a study reports.
This new method uses a novel form of positron emission tomography (PET) imaging alongside CT scans to detect tumors that produce and release adrenocorticotropic hormone (ACTH), which can cause Cushing’s disease.
In this study, its use “successfully identified [tumors] in all 24 patients” tested, according to the researchers.
“This hybrid imaging technique could in theory enable the assessment of both functionality and anatomical delineation simultaneously,” the team wrote. That means it could theoretically tell clinicians both where a tumor is and whether it’s releasing ACTH.
The study, “A novel molecular imaging technique using [68Ga]Ga-mDesmo PET-CT for localizing tumors in Cushing’s disease,” was published in the European Journal of Nuclear Medicine and Molecular Imaging. It was funded in part by the Endocrine Society of India.
Detection of tumors ‘needs a multipronged approach’
In Cushing’s syndrome, high levels of the hormone cortisol can lead to a variety of symptoms, such as weight gain, skin changes, and fatigue. Cushing’s in some cases is ACTH-dependent — meaning it’s caused by an excess of ACTH, which is a signaling molecule that promotes cortisol production.
Tumors in the pituitary gland, a pea-sized gland in the brain, are sometimes the source of excess ACTH. This is known as Cushing’s disease.
However, ACTH-dependent Cushing’s can also be caused by tumors found outside the pituitary gland, which is referred to as ectopic Cushing’s syndrome. People with ectopic Cushing’s may also have pituitary tumors that don’t produce excessive amounts of ACTH, further complicating the diagnosis process.
With multiple possible underlying causes, “detection of the source of ACTH in ACTH-dependent [Cushing’s syndrome] is always challenging and needs a multipronged approach,” the research team wrote.
To properly identify the source, and have enough information to surgically remove the disease-causing tumor, clinicians need both anatomical information — to know where a tumor is — and functional information, or whether it’s releasing ACTH.
Contrast-enhanced MRIs, known as CE-MRIs, are a type of imaging test often used in the diagnosis of Cushing’s disease. While a CE-MRI can provide anatomical information, it can not, however, give functional data.
Additionally, the researchers noted, many tumors in people with Cushing’s disease are small, measuring less than 10 mm in diameter, and may not show up on a CE-MRI.
To overcome some of these challenges, a team led by scientists from the Postgraduate Institute of Medical Education and Research, also known as PGIMER Chandigarh, designed an imaging technique called [68Ga]Ga-mDesmo PET-CT. It relies on PET technology, which uses nontoxic radioactive molecules combined with scanning technology to obtain a detailed picture of tissues and organs.
The new PET marker, [68Ga]Ga-mDesmo, contains a radioactive tag that allows it to be tracked during the scan. It is also designed to bind to a receptor that is often present on ACTH-producing pituitary tumors, thus providing both anatomical and functional data, according to the team.
Novel imaging technique had 100% accuracy regardless of tumor size
In this study, 30 patients with ACTH-dependent Cushing’s had PET/CT scans with the new molecule, as well as CE-MRI scans for comparison. Most (80%) had Cushing’s disease. A total of 17% had ectopic Cushing’s syndrome, and the remainder had adrenal Cushing’s. The patients had a mean age of 33.5.
[68Ga]Ga-mDesmo PET-CT identified 100% of pituitary tumors in patients with Cushing’s disease, regardless of size, the data showed.
CE-MRI, meanwhile, also had 100% accuracy in the seven Cushing’s disease patients whose tumors measured at least 10 mm in diameter. However, its accuracy dropped to 53% in patients with tumors measuring less than 10 mm.
Besides correctly identifying the presence of pituitary tumors, [68Ga]Ga-mDesmo PET-CT did not return any false positives for pituitary tumors among patients with ectopic or adrenal Cushing’s. This indicated that the marker molecule was not targeting all cells that produce ACTH, only those specifically found in tumors.
[This study] provides valuable insights into the diagnostic capabilities of [68Ga]Ga-mDesmo imaging in cases of ACTH-dependent Cushing’s … particularly in challenging scenarios.
“This study highlights the potential of [68Ga]Ga-mDesmo imaging as a superior amalgamation of both anatomical and functional insights into the presence of [ACTH-producing pituitary tumors],” the team wrote.
Replicating these results in a larger group of participants will be needed to validate the new imaging technique, the researchers stressed. Further, while the radioactive marker has a short half-life and therefore should not carry a high risk of radiation toxicity, more data may also be needed to help establish safe dosage practices for the new molecule, the team noted.
Overall, however, the team noted as a study strength that this work “provides valuable insights into the diagnostic capabilities of [68Ga]Ga-mDesmo imaging in cases of ACTH-dependent Cushing’s … particularly in challenging scenarios.”
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