Variation in Blood Vessel Anatomy May Raise Risk of CTEPH

Marisa Wexler MS avatar

by Marisa Wexler MS |

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Many people with chronic thromboembolic pulmonary hypertension or CTEPH have a particular anatomical variation called May-Thurner anatomy, which may increase the risk of developing this rare disease type, according to researchers.

A new study found this anomaly is very common in individuals with CTEPH, with nearly 30% of patients referred in the last five years to Temple University’s CTEPH program shown to have May-Thurner anatomy, called MTA.

“Very little has been known about the prevalence of MTA and its association with CTEPH,” Riyaz Bashir, MD, director of vascular and endovascular medicine at Temple University Hospital, in Philadelphia, and the study’s senior author, said in a press release.

“Now we know that it is actually quite common, and there are therapies that can improve treatment and quality of life for these patients,” Bashir said.

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The study, “May-Thurner Anatomy in Patients With Chronic Thromboembolic Pulmonary Hypertension: An Important Clinical Association,” was published in JACC: Cardiovascular Interventions.

CTEPH is a particular kind of pulmonary hypertension that results from blood clots in the lungs’ blood vessels, which block the normal flow of blood.

One of the established risk factors for developing CTEPH is called deep vein thrombosis or DVT, which occurs when a blood clot (thrombus) forms in a “deep vein” in the body, usually a large vein in the leg. These clots can then travel through the bloodstream and end up elsewhere in the body, such as in the lungs to cause CTEPH.

“There are many risk factors for CTEPH, but DVT is especially important, owing to its frequent involvement of large veins in the legs and pelvis,” Bashir said.

The iliac arteries are a set of large blood vessels that act as a major highway for blood traveling to the legs. There are two iliac arteries, right and left, one for each leg.

MTA is a particular anatomical variation in which the right iliac artery compresses the left iliac vein against the lower back. This abnormal pressure can lead to certain circulatory disorders — including, notably, DVT.

“Compression of the iliac vein leading to DVT can occur at different anatomical sites in the pelvis, including the anatomical location of MTA,” Bashir said.

Given that MTA can increase the risk of DVT, and that DVT, in turn, can increase the risk of CTEPH, it follows logically that MTA may increase the risk of this type of pulmonary hypertension, or PH. However, according to Bashir, “no one has really looked at MTA prevalence in CTEPH patients, even though MTA may have been a primary cause of this condition and can be treated very effectively.”

Now, Bashir and other investigators analyzed imaging data from 148 people with CTEPH who were seen at Temple University Hospital between 2016 and 2020.

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The results showed that almost a third (29.7%) of the CTEPH patients had MTA.

“MTA is very common in patients with CTEPH,” the researchers concluded. Notably, missed diagnoses have been proposed as an explanation for the reported low clinical prevalence of MTA-related DVT.

Statistical analyses showed that CTEPH patients with MTA were significantly more likely to have DVT in their lower limbs than those without the anomaly. Patients with MTA also were significantly more likely to undergo pulmonary thromboendarterectomy, a surgical procedure to remove clots from blood vessels in the lungs.

Collectively, the results suggest that having MTA might increase a person’s risk of this disease.

“Our hope now is that we can use existing screening methods for iliac vein compression and MTA to improve treatment for CTEPH patients and to identify patients who may be at risk of CTEPH, based on history of DVT and recurrent pulmonary [clots blocking blood flow],” Bashir said.

“Given the importance of pelvic venous obstruction in DVT, we suspect that sites of iliac vein compression other than MTA are additional causes of CTEPH,” he added, noting a potential direction for future research.