Researchers detailed a rare case of delayed hematoma recurrence following cyst formation after radiosurgery for brain arteriovenous malformation
Arteriovenous malformation (AVM) is a vascular condition in which blood vessels are improperly formed, which causes blood to bypass the usual network of capillaries and flow directly from the arteries to veins through abnormal tangles of blood vessels. This can deprive the surrounding tissues from oxygen and lead to complications such as headaches, seizures, or internal bleeding.
Stereotactic radiosurgery (SRS)— a radiation therapy that delivers highly focused radiation beams to precise targets– has emerged as a promising non-invasive treatment option for AVMs, particularly effective for those located in sensitive or eloquent brain areas. However, the long-term post-treatment complications such as radiation-induced cyst formation (CF) have been poorly understood.
To address this critical gap, a team of researchers led by Dr. Iñigo L. Sistiaga from University Hospital Cruces, Spain has published a detailed case report describing a rare but serious delayed complication. Conducted in collaboration with Biocruces Bizkaia Health Research Institute and the University of the Basque Country, Spain, the published online in Volume 11, Issue 01 of the
Chinese Neurosurgical Journal on January 13, 2025.
The case describes how a 28-year-old male—who had undergone SRS treatment for AVM— developed an enlarging brain cyst (fluid-filled tissue sac) after ten years post-treatment. This cyst was initially asymptomatic but grew steadily over several years. Despite a surgical procedure to drain the cyst, the patient later experienced a recurrence in the form chronic encapsulated expanding hematoma (CEEH), a condition where a blood clot progressively enlarges within a fibrous capsule which required surgical removal of the affected lobe of the brain (lobectomy).
On a further inspection, it was noted that there was a presence of an angiomatous nodule within the cyst which was overlooked during the initial surgical drainage. Angiomatous nodules are small, benign (non-cancerous) growths composed mainly of blood vessels. It is possible that the ongoing hemorrhage was a result of the same—eventually transforming the cyst into a chronic encapsulated hematoma.
According to the case, CF and CEEH may not be separate conditions but actually a part of a pathological progression. The case also challenges the current treatment strategies for late-onset cysts, especially those cysts that show enhanced nodules during imaging with contrast dye. The authors also recommend aggressive removal of both cyst and its associated vascular nodules (nodes of blood vessels), rather than simply draining the cyst.
“
What appears to be a harmless cyst might, in fact, be the early stage of a more serious complication,” says Dr. Sistiaga, “
If a contrast-enhancing nodule is seen, aggressive surgical removal might be the only resort to prevent a more dangerous recurrence.”
Moreover, the case also stresses on the need for long-term follow-up post radiosurgery. Although the angiography suggested complete removal of AVM, there were subtle radiation-induced changes which were visible as early as five years post-treatment. The authors argue that these signs should be considered critical to evaluate the risk of late complications even if the patient is asymptomatic.
“
According to literature, estimated incidence of CF after SRS surgery is only under 5%, while CEEH is even rarer. However, when combined, these complications may affect up to 7% of the total treated patients” notes Dr. Sistiaga.
The delayed onset and nonspecific presentation of these complications raise the risk of underdiagnosis, particularly in the absence of routine follow-up imaging. As SRS becomes more widely used for AVM treatment, this case highlights the urgent need to refine follow-up protocols, enhance diagnostic awareness, and reconsider surgical approaches to prevent severe neurological outcomes.
***
Reference
Titles of original paper: Recurrence of chronic encapsulated hematoma following cyst formation after stereotactic radiosurgery for brain arteriovenous malformations: a case report
Journal:
Chinese Neurosurgical Journal
DOI:
10.1186/s41016-025-00387-6