Study compares tools for Cushing’s diagnosis, tumor localization

Magnetic resonance imaging (MRI) is a useful tool for pinpointing the location of a pituitary tumor that causes Cushing’s disease prior to surgery, a recent study reported.

However, study findings indicate that bilateral inferior petrosal sinus sampling (BIPSS), an invasive diagnostic procedure, is more accurate for the initial Cushing’s diagnosis, since in some cases MRI may fail to detect disease-driving tumors.

“The combined use of a multimodality diagnostic approach, including clinical presentations, biochemical tests, MRI, and BIPSS, could improve the accuracy of preoperative diagnostics,” the researchers wrote.

Findings were detailed in the study, “Comparison of the preoperative diagnostic accuracy of BIPSS versus MRI for Cushing disease: a single-centre experience,” was published in the journal BMC Endocrine Disorders.

Cushing’s disease is caused by a tumor in the brain’s pituitary gland that releases excessive amounts of a signaling molecule called adrenocorticotropic hormone (ACTH). High ACTH levels drive the production of the stress hormone cortisol, which then triggers the typical symptoms of Cushing’s.

MRI and BIPSS are both techniques that may be used in the workup of diagnosing Cushing’s disease. In BIPSS, blood samples from the veins draining the pituitary gland are collected and tested for ACTH. This can be used to confirm the presence of a pituitary tumor, which is typically signaled by increased ACTH levels. MRI uses powerful magnetic fields to generate images of the body’s internal structures, which can be used to identify pituitary tumors.

The most common first-line treatment for Cushing’s disease is surgery to remove the disease-causing tumor. To accurately remove the tumor, it’s helpful to know exactly where in the pituitary gland it resides. Both BIPSS and MRI may be useful in this regard. While MRI can help clinicians directly visualize the tumor, BIPSS can identify the side of the pituitary gland that is overproducing ACTH, which also is typically the one where the tumor can be found.

In this study, scientists in China compared the utility of BIPSS and MRI in the diagnostic workup and treatment of Cushing’s disease. The study included 29 patients who underwent BIPSS and MRI evaluation at the scientists’ center from 2017 to 2021.

All patients — 23 women and six men, with a mean age of 37.5 years — had symptoms caused by excess cortisol levels that were suggestive of Cushing’s syndrome. All but one had a positive test result on BIPSS, confirming the diagnosis of Cushing’s disease. The one outlier was ultimately found to have a disease-driving tumor in another region of the body, indicating that individual did not have true Cushing’s disease.

On MRI scans, pituitary tumors were identified in 26 of the 29 patients assessed. That means BIPSS detected two pituitary tumors that were missed by MRI.

BIPSS ‘most accurate’

“BIPSS was the most accurate method (gold standard) for establishing a preoperative diagnosis of [Cushing’s disease] and was more sensitive than MRI for diagnosing [small pituitary tumors],” the researchers wrote.

Of the 28 patients diagnosed with Cushing’s disease, all but one underwent surgery to remove the tumor. The outlier instead underwent radiation therapy.

In all cases where an MRI scan had identified the disease-causing tumor, the location of the tumor based on the scan was consistent with where the tumor was found during surgery. However, tumor location found in surgery was consistent with results from BIPSS in only 19 of 27 cases.

Based on these results, researchers concluded that, when MRI data is available to predict tumor location, it usually is more reliable than BIPSS data. The team said that these and other diagnostic tools should be used together to provide the best possible care for people with Cushing’s.