The Role of Surgical Resection for Metastatic Brain Tumors

Introduction

Brain metastases are 10 times more common than any primary brain neoplasm. Approximately 20–40% of patients suffering from systemic cancer develop symptomatic brain metastases, translating into a huge disease burden annually ( ). In adults, lung cancer is the most common source of brain metastases (50–60%), followed by breast cancer (15–20%) and melanoma (5–10%) ( ). The optimal management of brain metastases remains controversial. Whole-brain radiotherapy (WBRT) and local treatment, including surgery and radiosurgery, are considered the cornerstones of treatment. The treatment paradigm for brain metastases is rapidly evolving with emerging technologies, and multiple guidelines and controversies exist regarding each treatment modality.

Surgical treatment was first introduced as a treatment for brain metastases in 1926 ( ). Initially, the morbidity and mortality of surgical procedures was unacceptably high. Improved surgical techniques and developments in the field of neuroanesthesia, neuroimaging, neuromonitoring, and postoperative care have significantly improved outcomes, and, for a select patient population with a single brain metastasis, surgical resection followed by radiotherapy is now the gold standard for the treatment of brain metastasis ( ). It is worth noting that most of the patients treated for brain metastases now die of extracranial disease ( ). This is an important consideration because, although most studies have used overall survival as the main endpoint, survival is probably not the best parameter to measure the efficacy of existing brain-specific therapeutic modalities ( ).

Surgical resection

Indications of Surgical Resection

The main aim of surgery in treating patients with brain metastases is to lengthen the survival times while improving neurologic conditions and performance status ( ). Because of recent technical advances in radiosurgery, patients treated with stereotactic radiosurgery (SRS) have outnumbered those treated with surgery. However, only surgical intervention allows rapid debulking of tumors with significant mass effect and can be considered a life-saving intervention in patients with herniation syndromes and neurologic deficits ( ). It also allows for restoration of cerebrospinal fluid flow, relieving intracranial pressure, and lowers steroid dependence. Surgery can also assist in managing medically refractory seizures caused by tumors ( ). In most cases, the primary goal of surgery is gross-total resection of the tumor with minimal disruption of normal brain tissue. Data from a retrospective review showed that early postoperative Karnofsky performance status (KPS) scores were improved in 59% of patients, unchanged in 32%, and worse in 9% of patients who had undergone microsurgical tumor removal. Surgery also allows for histologic confirmation of the diagnosis of brain metastases ( ).

Surgical Technique

Prior to taking the patient to the operating room, outlining the preoperative surgical plan, utilizing structural and functional imaging modalities, is of paramount importance. Utilization of intraoperative image guidance, microsurgical techniques, and perioperative neurologic monitoring reduces the possibility of surgery-related mortality and morbidity. Tumors can be resected either in a piecemeal fashion or en bloc . Data have shown that piecemeal resection of the tumor is associated with a significant increase in risk of local recurrence when compared to en bloc resection ( ). En bloc resection is particularly instrumental when dealing with posterior fossa lesions; however, an eloquent location within the brain parenchyma significantly limits en bloc resection. In those cases, partial resection should be performed and radiosurgery can be used for the residual tumor. Despite seemingly complete resections, the reported local recurrence rate in the surgical bed is 10–34% at 1 year following surgery and radiotherapy ( ). It is mostly attributable to tumor infiltration, which can vary with different histologic tumor types, with aggressive tumors infiltrating up to 3 mm beyond the surgical bed ( ). The concept of “microscopic total resection” in which microscopic infiltrating tumor cells within a normal-looking brain parenchyma are removed within a 5-mm area in the peritumoral bed region, has also been evaluated by a Korean group ( ). They were able to show that this method of resection is as effective in reducing local recurrence as gross total resection supplemented with radiotherapy.

Clinical evidence

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