MRI Better Than IPSS at Locating Pituitary Tumors, Researchers Conclude

Magnetic resonance imaging (MRI) is a better way to find pituitary tumors in Cushing’s disease than inferior petrosal sinus sampling (IPSS), according to the results of a recent record review.

The study, “Lateralization of inferior petrosal sinus sampling in Cushing’s disease correlates with cavernous sinus venous drainage patterns, but not tumor lateralization,” was published in the journal Heliyon.

IPSS is an established diagnostic technique used to locate tumors of the pituitary gland — also called microadenomas — by measuring the levels of the adrenocorticotropic hormone (ACTH) in veins draining from the pituitary gland. Pituitary tumors can trigger an overproduction of ACTH, causing the adrenal glands to overproduce cortisol, resulting in Cushing’s disease.

The veins with more ACTH are thought to indicate the side of the pituitary on which a tumor has grown. Correctly identifying these sites is critical to guiding timely treatment decisions, such as surgical tumor removal.

Some studies, however, suggest that individual variations in the anatomy of the veins, called parasellar veins, which drain the pituitary, complicate predicting these locations.

Because of this, the authors of the present study asked whether parasellar venous drainage (VD) patterns affected IPSS results more than actual tumor location. A review of patient records showed them that while IPSS and parasellar venous drainage were correlated nearly perfectly, neither corresponded well with actual tumor sites, as shown surgically.

The best predictions, they found, came from MRI readings.

The investigators examined records of 17 lab-confirmed cases of Cushing’s disease from January 2014 to October 2018.

IPSS identified eight patients with right-sided microadenomas, five left-sided, and four patients with symmetrical tumors. These results perfectly matched parasellar VD patterns, resulting in a 100% correlation between the two metrics.

MRI findings, on the other hand, showed two patients with right, three with left, nine with central, two with left and central, and one with right and central adenomas.

Surgery confirmed the precise locations of these patients’ tumors. Closely paralleling the MRI findings, three patients had tumors on the right side, one on the left, nine central, three left-and-central, and one right-and-central.

In contrast to the strong association the findings had with MRI results (an 86% match), the researchers found poor correlation between surgical findings and IPSS results (a 25% match).

These results led the authors to conclude that IPSS results depend on parasellar VD patterns and not on the actual sites of microadeomas. Because MRI and surgical findings complement each other well, however, the authors recommend using MRI rather than IPSS to guide surgical decisions.