Tracing the Dural Tail with Image-Guided Surgery

The Simpson Grading: Is It Still Valid?

The Simpson Grade was introduced in the era of limited resources, outdated techniques, and rudimentary surgical and imaging technologies. With the advent of modern techniques including pre- and post-operative imaging, microsurgical and endoscopic techniques, advanced histopathology and molecular analysis and adjuvant radiotherapy, the utility of the Simpson Grade scale for prognostication of recurrence after meningioma resection has become less useful. While the extent of resection remains an important factor in reducing recurrence, a subjective naked-eye criteria to Grade extent of resection cannot be generalized to all meningiomas regardless of their location or biology. Achieving the highest Simpson Grade resection should not always be the goal of surgery. It is prudent to take advantage of all the tools in the neurosurgeons’ armamentarium to aim for maximal safe resection of meningiomas. The primary goal of this study was to review the literature highlighting the Simpson Grade and its association with recurrence in modern meningioma practice. A PubMed search was conducted using terms “Simpson”, “Grade”, “meningioma”, “recurrence”, “gross total resection”, “extent of resection” “human”. A separate search using the terms “intraoperative imaging”, “intraoperative MRI” and “meningioma” were conducted. All studies reporting prognostic value of Simpson Grades were retrospective in nature. Simpson Grade I, II and III can be defined as gross total resection and were associated with lower recurrence compared to Simpson Grade IV or subtotal resection. The volume of residual tumor, a factor not considered in the Simpson Grade, is also a useful predictor of recurrence. Subtotal resection followed by stereotactic radiosurgery has similar recurrence-free survival as gross total resection. In current modern meningioma surgery, the Simpson Grade is no longer relevant and should be replaced with a grading scale that relies on post-operative MRI imaging that assess GTR versus STR and then divides STR into > or <4−5 cm3, in combination with modern molecular-based techniques for recurrence risk stratification.

Navigated resection of giant intracranial meningiomas based on intraoperative 3D ultrasound

BACKGROUND

Surgical resection of giant meningiomas may pose different challenges. Normal brain tissue is often compressed to the limit and is vulnerable to further traction. In addition, severe intraoperative bleeding may be a problem as many giant meningiomas are vascularised with deep feeding vessels entering from the skull base. Neuronavigation based on preoperative imaging can be of limited use as there may be extensive brain shifts during surgery.

METHOD

We have retrospectively evaluated navigated resection based on intraoperative 3D ultrasound in a series of 15 giant meningiomas with a diameter of more than 5 cm. A pre- and postoperative MRI was preformed in all patients. Preoperative and postoperative neurological function was assessed.

FINDINGS

We were able to safely perform ultrasound-guided intracapsular gross total resection of tumour tissue in all patients. Twelve out of 15 patients were radically operated (Simpson grade I and II). Major feeding arteries and adjacent normal arteries could be identified by ultrasound power Doppler angiography. In one patient we were not able to indentify important venous structures. All patients experienced postoperative improvement of their symptoms. Postoperative MRIs did not reveal significant ischemic changes in adjacent normal brain tissue. The mean duration of hospitalisation after surgery was 4.9 days.

CONCLUSION

We present a method of ultrasound-guided resection of giant meningiomas. The method enables image-guided resection through narrow approaches that minimise traction. Power Doppler angiography allows the identification of feeding vessels that may be coagulated to limit bleeding. Likewise, normal arteries can be avoided during surgery. The tumour capsule is often surprisingly easy to remove from the arachnoid membrane after gross intracapsular tumour reduction.