Asymmetry of blood outflow patterns from the inferior petrosal sinus (IPS) — the two main veins which drain the pituitary gland — does not make it more difficult to figure out which side of the gland has an adenoma that is causing Cushing’s disease, a study suggests.
Titled “Influence of inferior petrosal sinus drainage symmetry on detection of adenomas in Cushing’s syndrome,” the study was published in the Journal of Radiology.
Cushing’s disease is commonly caused by an adenoma — a type of tumor that’s usually not cancerous — on the pituitary gland. This results in increased production of adrenocorticotropic hormone (ACTH), which stimulates the production of cortisol. This, in turn, leads to increased production of cortisol by the adrenal glands.
Although magnetic resonance imaging (MRI) scans can sometimes detect small pituitary adenomas, the “gold standard” for diagnosis is bilateral IPS sampling (BIPSS). In BIPSS, blood samples are taken from the veins that drain the pituitary gland. The levels of ACTH in these samples are compared to ACTH levels in blood from other parts of the body to see whether a pituitary tumor is indeed responsible for observed Cushing’s disease.
Since samples are taken from either side — the reason it’s called “bilateral” — BIPSS can help determine on which side of the pituitary gland an adenoma is growing.
However, in the real world, things are messy, and the human body is not perfectly symmetrical. In fact, it’s not uncommon for there to be some differences in the IPS on either side, in terms of how they are structured and drained. Researchers questioned if asymmetry of the IPS could be a barrier in accurately and precisely diagnosing the location of an adenoma via BIPSS.
To find out, the investigators reviewed reports of Cushing’s disease patients treated at their hospital from 1997 to 2016. These included data for 38 people — 31 females and 7 males, average age 45 years — who were referred for BIPSS after an MRI failed to figure out the location of a pituitary adenoma.
Among these patients, IPS outflow patterns were reported to be symmetric in 19 and asymmetric in 12. For the remaining patients, no data on symmetry was available.
Adenoma prediction was slightly better among people with symmetric IPS outflow patterns as compared with those with asymmetric patterns (100% vs. 93%). However, this difference did not reach statistical significance, meaning it’s possible that any difference observed was just the result of random chance.
Additionally, clinical outcomes were not significantly different between these two groups. After treatments such as surgery, remission was reported in 15 (88%) patients with symmetrical IPS drainage, and in nine (82%) with asymmetrical drainage.
“Asymmetric venous outflow does not seem to significantly influence the accuracy with which the adenoma side can be predicted, nor does it have an influence on the remission rates in patients with [Cushing’s disease],” the researchers concluded. However, they noted that the study is limited by its small sample size and wide timeframe, during which technologies have changed. The investigators say more research will be needed to validate these results.