Endoscope-assisted treatment for delayed cystic radiation necrosis after stereotactic radiosurgery for metastatic brain tumors: illustrative cases

Abstract

Background: Cystic formation due to radiation necrosis in metastatic brain tumors is a rare condition. Surgical intervention is necessary if symptoms develop. Additionally, excising radiation necrosis lesions within the cyst is essential to prevent recurrence. Neuroendoscopic surgery is a minimally invasive method suitable for treating cystic diseases and accessing deep lesions in the brain. The authors herein present a method for removing radiation necrotic tissue from deep lesions of cystic radiation necrosis using neuroendoscopy.

Observations: Endoscopic surgery was performed in two patients with symptomatic cystic radiation necrosis. Both cases involved multilocular cysts, with radiation necrosis located deep within the cyst. The authors performed a small craniotomy of approximately 3 cm and opened the cyst. After removing its contents, an endoscope was used to closely observe the interior of the cyst. Removal of the septum within the cyst allowed the endoscope to be inserted deeply. The authors identified and excised the nodular lesion diagnosed as radiation necrosis in the deep tissue. Following the surgery, the cyst shrank rapidly, and symptoms disappeared. Both patients showed no recurrence of the lesions.

Lessons: The authors performed minimally invasive surgery and achieved good outcomes. Endoscopic surgery was considered beneficial for treating cystic radiation necrosis. https://thejns.org/doi/10.3171/CASE24250.

Keywords: cystic radiation necrosis; endoscopic surgery; metastatic brain tumors; stereotactic radiosurgery.

FIG. 1.

Case 1. Axial T2-weighted and enhanced T1-weighted MRI. Initial MRI upon the diagnosis of lung cancer revealed a metastatic tumor in the right parietal lobe (A and B). Images obtained 24 months post-SRS showed radiation necrosis with multiple cysts still evident (C and D). Preoperative images showed an enlarged multilayer cyst with an edematous-appearing area and an enhanced lesion within the cyst (E and F). The cystic lesion notably disappeared, with only mild edema observed 50 months following endoscopic surgery (G).

FIG. 2.

Case 1. A 3-cm-diameter craniotomy was performed (A). Close observation of the interior of the cyst using an endoscope revealed septa deep within the cyst (B). Subsequently, the septa were removed. Reddish nodular lesions were visible deep within the cyst (C). We coagulated the lesion with bipolar forceps and removed it piecemeal. Pathological analysis confirmed radiation necrosis without evidence of tumor recurrence. As the removal proceeded, the deep cyst wall became visible (D and E). After the removal, we performed coagulation of the attachment area (F). The arrowhead indicates the septum, and arrows indicate the nodular lesion.

FIG. 3.

Case 2. Axial T2-weighted and enhanced T1-weighted MRI. Pre-SRS MRI showed a metastatic brain tumor in the left frontal lobe (A and B). Images obtained 42 months after SRS revealed an enhanced lesion with a small cyst in the left frontal lobe (C and D). Preoperative images showed the enlarged cyst, with an enhanced lesion located deep within (E and F). MRI performed 6 months postoperatively showed shrinkage of the cystic lesion (G).

FIG. 4.

Case 2. A small craniotomy was performed (A). Drainage of the fluid within the cyst and removal of the septa deep within the cyst followed (B). Close observation of the interior of the cyst revealed a reddish nodular lesion located deep within the cyst (C). We identified the border between the reddish nodular lesion and the surrounding tissue (D). Subsequently, we resected the nodular lesion diagnosed as radiation necrosis (E). After removing the lesion, we confirmed that there was no residual lesion and could observe the cyst wall deep inside (F). The arrowhead indicates the septum, and arrows indicate the nodular lesion.