In Situ Pulmonary Artery Thrombosis: Unrecognized Complication of Radiation Therapy

Our plain-English summary of In Situ Pulmonary Artery Thrombosis: Unrecognized Complication of Radiation Therapy, by J. Ahuja, G.S. Shroff, M.F. Benveniste, et al (AJR. American Journal of Roentgenology, 2020).

The study

• Authors: J. Ahuja, G.S. Shroff, M.F. Benveniste, E.M. Marom, M.T. Truong, C.C. Wu
• Journal: AJR. American Journal of Roentgenology
• Published: 2020;215(6):1329-1334
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

OBJECTIVE. The purpose of this study is to evaluate the CT and clinical characteristics of in situ pulmonary artery thrombosis (PAT) associated with radiation therapy (RT). MATERIALS AND METHODS. A database search was performed to identify patients who had PAT develop after receiving RT. The CT characteristics of PAT, including the number, location, and appearance of filling defects as well as the presence of associated lung fibrosis, were recorded. The terminology (in situ thrombosis vs acute or chronic pulmonary embolism) used by the interpreting radiologists to describe PAT, the time between the completion of RT and development of PAT, the change in the size of the PAT, and observation of any new thrombi and emboli on follow-up imaging, were also recorded. RESULTS. Of the 27 patients in the study cohort, 22 (81%) had lung cancer and five (19%) had mesothelioma. Most PATs were solitary (93%) and nonocclusive (96%) and formed an obtuse angle to the vessel wall (89%). All PATs were eccentric within the involved PA and were located within the RT volume. The time from completion of RT to initial diagnosis of PAT on CT ranged from 53 to 2522 days (mean, 675 days). Radiation-induced lung fibrosis was present in the ipsilateral lung in all patients. No evidence of additional PA filling defects that suggested embolization were seen on follow-up images of any of the patients, even those who did not receive anticoagulant therapy. CONCLUSION. In situ PAT associated with RT, which to our knowledge has not previously been described in the English literature, has imaging features different from those of acute pulmonary emboli and does not appear to embolize. Radiologist awareness of PAT can facilitate accurate diagnosis and impact management.

In plain English

This retrospective study reviewed CT scans and medical records of cancer patients who developed a blood clot inside a lung artery (in situ pulmonary artery thrombosis) after radiation therapy. The article does not discuss asbestos. Of the 27 patients, 22 had lung cancer and five had mesothelioma. None of the 27 had symptoms, and the clots were found on routine cancer follow-up scans. In every patient the clot lay inside the area that had been irradiated and off-center in the artery, and the lung it supplied showed radiation scarring (fibrosis). Clots were single in 25 patients and did not block the artery in 26. They were first diagnosed 53 to 2522 days after radiation ended (mean 675 days). In 13 patients the clot was not reported when it first appeared. On follow-up, no patient developed new clots elsewhere in the lung arteries that would have suggested a clot breaking loose. This was also true of the 11 patients not given anticoagulants. The authors concluded that these clots look different from acute pulmonary emboli and do not appear to embolize. They noted the small sample and the lack of pathologic confirmation.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective review of radiology reports, CT images and medical records (case series)
• Who was studied: 27 patients (19 men, 8 women; mean age 71, range 54 to 90). They were selected from 36 patients whose radiology reports from 2013 through 2019 at a large teaching hospital mentioned pulmonary artery thrombosis after radiation therapy. Nine were excluded: six for missing follow-up images or clinical notes, two for presumed tumor thrombosis, and one for stump thrombosis after lobectomy.
• Exposure: Radiation therapy: intensity-modulated RT in 14 patients, stereotactic beam RT in 2, and intensity-modulated proton therapy in 9; records were not available for 2. Doses ranged from 45 to 74 Gy. The article does not address asbestos exposure.
• Main results:
  • Primary cancer was lung cancer in 22 of 27 patients (81%) and mesothelioma in 5 (19%).
  • All 27 patients had no symptoms when the clot was first diagnosed; it was found on routine cancer surveillance imaging.
  • The clot was solitary in 25 patients; 2 patients had more than one clot in the same lobe.
  • The clot did not block the vessel in 26 patients and blocked it in 1.
  • Clots formed an obtuse angle to the vessel wall in 24 patients (89%) and an acute angle in 3 (11%).
  • In all patients the clot was off-center (eccentric) within the artery.
  • In all patients the clot was located only within the radiation therapy volume.
  • In all patients, CT showed radiation-induced lung fibrosis in the lung supplied by the affected artery.
  • Time from the end of radiation therapy to diagnosis of the clot ranged from 53 to 2522 days (mean 675 days).
  • In 13 patients the clot was not reported when it first appeared on CT. The delay in diagnosis ranged from 11 to 1217 days (mean 369 days).
  • When first identified, the radiologists interpreted the findings as in situ or chronic thrombosis in 20 patients and as acute pulmonary embolism in 7.
  • 16 patients received anticoagulation and were followed for a mean of 410 days. The clot resolved in 5, decreased in 4 and stayed stable in 4.
  • Among the anticoagulated patients, the clot grew in 3. Based on chart review, this was thought to be caused by not following treatment.
  • Among the 11 patients not given anticoagulation (followed a mean of 699 days), the clot was stable in 7 and grew in 4.
  • On follow-up imaging, no patient developed clots in other parts of the pulmonary arteries that would have suggested embolization.
• The authors' conclusion: The authors concluded that in situ pulmonary artery thrombosis associated with radiation therapy has imaging features different from acute pulmonary emboli and does not appear to embolize. They said it needs to be distinguished from pulmonary embolism because prognosis and management differ.
• Limitations the authors state:
  • Small sample size.
  • Because radiologists under-reported or misread this finding, cases that were never reported would not have been found and included.
  • There was no pathologic confirmation that the clots were in situ thrombosis.
  • The authors state that a larger systematic study is needed to clarify the association between in situ pulmonary artery thrombosis and radiation therapy.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Fibrosis, Lung Cancer, Mesothelioma.

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• Rounded atelectasis complicated by obstructive pneumonia and pulmonary arterial thrombosis — C.H. Chen, L. Newman (1990)
• Jugular vein thrombosis associated with distant malignancy — B.M. Carrington, J.E. Adams (1988)
• Mesothelioma and internal carotid artery occlusion: acute ischemic stroke and efficacy of emergency carotid thrombectomy — E. Ferrero, M. Ferri, et al. (2010)
• Vascular and thrombogenic effects of pulmonary exposure to Libby amphibole — J.H. Shannahan, M.C. Schladweiler, et al. (2012)
• Unusual radiologic findings in the thorax after radiation therapy — B. Mesurolle, S.D. Qanadli, et al. (2000)
• Dosimetric Correlates of Pulmonary Toxicity in Patients with Malignant Pleural Mesothelioma Receiving Radiation Therapy to the Intact Lungs — M.R. Thompson, V.A. Dumane, et al. (2019)

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