23 Natural History and Management Options of Convexity Meningioma

Chien Yew Kow and Arnold Bok

Abstract

The management of convexity meningiomas remains controversial and usually depends on the preference of the neurosurgeon who manages the patient. The size, location, vascularity, and growth rate of a meningioma play a role, as do the preference of the patient and the opinion and experience of the treating neurosurgeon. Weighing up the natural history of these lesions against the treatment injury risks remains key to successful management. In this chapter, we present the natural history and management options for convexity meningiomas.

Meningiomas are benign extra-axial growths that arise from the arachnoid cap cells present in the arachnoid granulations along the dura. They account for 36.4% of overall primary central nervous system (CNS) tumors and 53.4% of nonmalignant primary CNS tumors.1 The overall incidence is estimated at 7.75 per 100,000 population,¹ and this has increased over time due to the growing availability of neuroimaging. In general, meningiomas are more common among females, and the incidence increases with advancing age.^{1,​ 2} Uncommon malignant meningioma tend to be more prevalent among men.^{1,​ 2}

Convexity meningiomas are lesions that arise along the perimeter of the cranial vault with dural attachments not involving dural venous sinuses, the falx, or the skull base. Approximately 90% of all meningiomas are supratentorial, with 15 to 19% located along the convexity.^{3,​ 4} Convexity meningiomas have the greatest potential for cure as they lend themselves to total resection, including removal of the involved dura. The results of surgery for convexity meningiomas are generally better compared to other anatomical locations (1.7–9.4% morbidity and 0% 30-day mortality).^{24,​ 25}

Convexity meningiomas have traditionally been classified into several subtypes based on anatomic location: precoronal, coronal, postcoronal, paracentral, parietal, temporal, and occipital.⁵ Most convexity meningiomas are located with a component of the tumor anterior to the central sulcus as there is an increased density of arachnoid granulations anterior and adjacent to the coronal suture. In addition, convexity meningiomas can be morphologically classified as globoid (spherical, lobulated mass) or en plaque (flatter, carpetlike appearance infiltrating the dura).

Most convexity meningiomas are asymptomatic and are incidentally detected following radiological investigation for other unrelated clinical presentations. In symptomatic patients, headache is the most common complaint (39–48% of patients).^{24,​ 25} Convexity lesions around the precentral cortical area may cause contralateral weakness and focal motor seizures (Fig. 23.1), whereas tumors of the postcentral area may cause sensory deficits. Speech disturbance may arise from tumors compressing Broca’s or Wernicke’s area on the dominant hemisphere. Visual deficits may result from lesions overlying the temporal or occipital lobes. Up to 40% of patients with convexity meningiomas experience seizures preoperatively.

With greater availability of neuroimaging, incidental convexity meningiomas are becoming more prevalent. This leads to the management dilemma for asymptomatic patients. This chapter discusses the natural history and management options for convexity meningiomas.

23.2 Selected Papers on the Natural History of Convexity Meningioma

●Hashimoto N, Rabo CS, Okita Y, et al. Slower growth of skull base meningiomas compared with non-skull base meningiomas based on volumetric and biological studies. J Neurosurg 2012;116(3):574–580

●Lee EJ, Park JH, Park ES, Kim JH. “Wait-and-see” strategies for newly diagnosed intracranial meningiomas based on the risk of future observation failure. World Neurosurg 2017;107:604–611

Table 23.1 ^{6,​ 7,​ 8,​ 9,​ 10,​ 11,​ 12,​ 13,​ 14,​ 15,​ 16,​ 17,​ 18,​ 19,​ 20} summarizes the published studies on the natural history of convexity meningioma and the salient features associated with growth.

Table 23.1 Published studies on the natural history of convexity meningiomas

23.3.1 Size

Tumor size affects treatment recommendation. Larger tumor sizes are more likely to cause symptoms and, therefore, early surgical intervention.¹⁹ A review of the published series identified that larger initial tumor size predicts subsequent growth and the potential for treatment recommendation. Lee et al¹² found that meningiomas larger than 4 cm are likely to eventually cause neurological symptoms, with 65% of patients with a meningioma greater than 4 cm in their cohort developing new, or an aggravation of, neurological symptoms. Asymptomatic tumors less than 3 cm may be closely observed with regular radiological surveillance.

23.3.2 Growth Rate and Tumor Doubling Time

Studies of the natural history of meningiomas have found that most tumors grow very slowly. These were conducted on patients with incidental tumors with many remaining asymptomatic during the follow-up period. Based on our literature review, meningiomas have an annual growth rate of 0.7 to 4 mm per year and increase 3.6 to 20.4% per year in volumetric measures. This amounts to a tumor doubling time of 9.3 to 21.6 years. Growth rate for multiple meningiomas does not appear to be significantly different from solitary meningiomas.²¹ During a surveillance period, a 22 to 38% proportion of meningiomas demonstrated growth on linear measurement, and the proportion increased to 74 to 84% when volumetric measurements were utilized. However, inherent limitations of these natural history studies are characterized by a selection biased toward elderly patients subjected to observation and short follow-up period, ranging between 29 and 67 months.

Although most meningiomas are slow growing, some show aggressive or malignant biological behavior. Mean tumor doubling time was found to vary according to the World Health Organization (WHO) histological grading: 425 days (range: 138–1045 days) for grade I, 178 days (range: 34–551 days) for grade II, and 205 days (range: 30–472 days) for grade III.27

23.4 Risk Factors That Predict Tumor Growth

Identifying the risk factors that predict tumor growth is important for planning therapeutic strategies. The following factors are associated with tumor growth over time¹³:

●Presence of intratumoral T2 hyperintensity.

●Peritumoral cerebral edema.

●Larger tumor size (> 25 mm) at initial diagnosis.

●Younger patient age (< 60).

●Sphenoid ridge location.

In contrast, tumors with calcification (demonstrated on computed tomography [CT] and/or hypointensity on T2-weighted magnetic resonance imaging [MRI]) are associated with a slower growth rate.^{11,​ 13}

Furthermore, meningiomas are known to become larger during pregnancy and during the luteal phase of the menstrual cycle, suggesting that their growth may be related to female hormones. Furthermore, Ki-67 expression was found to be inversely correlated with progesterone receptor concentration, both in paraffin tissues and in cell culture. Most malignant meningiomas are PR negative, suggesting a loss of PR during tumor progression.

23.5 Recurrence

Tumor recurrence depends on the extent of surgical resection, histopathological grading, and the biological potential (Table 23.2).

Table 23.2 Predictors of tumor recurrence following surgical resection

Tumor location dictates the surgical resectability, which in turn affects the risk of recurrence. In 1957, Donald Simpson²⁶ introduced a five-grade classification of surgical removal of meningiomas, which correlated well with tumor recurrence. Convexity meningiomas are mostly amenable to optimal surgical resection and are associated with a low recurrence/progression rate.

The WHO classifies meningiomas into three histological grades based on (1) hypercellularity, (2) mitotic figures, and (3) presence of necrosis. Higher WHO grades are associated with a greater risk for recurrence and/or aggressive clinical behavior following surgical resection. Therefore, atypical or malignant meningiomas need to be closely followed up during the postoperative period.

In addition, high mitotic index is a significant predictor for shorter progression-free interval.

23.6 Selected Papers on the Treatment Options for Convexity Meningioma

●Alvernia JE, Dang ND, Sindou MP. Convexity meningiomas: study of recurrence factors with special emphasis on the cleavage plane in a series of 100 consecutive patients. J Neurosurg 2011;115(3):491–498

●Hasseleid BF, Meling TR, Rønning P, Scheie D, Helseth E. Surgery for convexity meningioma: Simpson Grade I resection as the goal—clinical article. J Neurosurg 2012;117(6):999–1006

●Morokoff AP, Zauberman J, Black PM. Surgery for convexity meningiomas. Neurosurgery 2008;63(3):427–433, discussion 433–434

●Kaur G, Sayegh ET, Larson A, et al. Adjuvant radiotherapy for atypical and malignant meningiomas: a systematic review. Neuro-oncol 2014;16(5):628–636

23.7 Treatment Options for Convexity Meningioma

Management of asymptomatic convexity meningiomas depends on their natural history, growth, and the assessment of the potential postoperative complications. In general, treatment options include observation, surgical resection, and radiotherapy. To rationalize treatment, management recommendation must consider tumor size, location, associated edema, patient’s age, and medical comorbidities.

Given the slow growth rate of convexity meningiomas, asymptomatic tumors should be observed with regular radiological surveillance. It should be noted that a small proportion of patients may become symptomatic during the observational period, ranging from 0 to 6.4%.15^{,​ 19,​ 20} For elderly patients, meningiomas often demonstrate a slower growth pattern, which, in conjunction with increased operative morbidity, may necessitate a more conservative approach in this cohort. For younger patients, asymptomatic tumors (< 3 cm) may be observed with regular radiological surveillance. Consideration for observation also needs to consider the potential higher-grade meningiomas, in which subsequent delay in intervention may result in potentially higher operative morbidity and impacting on long-term outcome.

23.9 Surgery

As good dural margin resection can often be achieved, surgical resection remains an effective curative treatment for convexity meningioma. The ease of resection depends on various factors, including location, size, blood supply, and involvement of critical structures. A Simpson grade 0 or 1 resection can be achieved in 80 to 95% of patients, as shown in Table 23.3.^{22,​ 23,​ 24,​ 25} This is generally associated with low retreatment risk, with rates between 2 and 10%, in line with previous findings by Simpson²⁶ and Jääskeläinen et al,²⁷ especially if the histology is benign. Extensive resection (Simpson grade 0) proposed by Kinjo et al²⁸ is likely to offer further protection against recurrence. For cases with bony invasion, we attempt to curet or drill out the tumor from the craniotomy bone flap prior to replacement, although a customized acrylic cranioplasty flap can also be used as an alternative in cases with extensive invasion.

Table 23.3 Surgical outcomes of convexity meningiomas in recently published studies

Contemporary surgical series (Table 23.3) demonstrate an overall lower procedural morbidity and higher complete resection rate with comparable retreatment risks. Prognosis for convexity meningiomas is excellent given its accessible location, which allows for total resection. Complete resection, even if there is en plaque growth, almost always excludes recurrence. In addition, when comparing patients of different age groups, Yano and Kuratsu¹⁹ found that 9.3% of patients who were older than 70 years suffered from persistent morbidity 3 months postoperation, compared to 4.4% of their younger counterparts. This series included resection of skull base meningiomas, which are usually more difficult to remove, and where surgery has a higher postoperative morbidity. Nonetheless, it remains important to be mindful of the risk of complications in the elderly.

The rationale of preoperative embolization is to facilitate surgical resection by minimizing perioperative surgical blood loss and softening the tumor. Existing data derived from several low-quality studies suggest that embolization decreases blood loss, but not operative time. Surgical complications may be reduced with preoperative embolization, but the available evidence is not clear. Meningiomas selected to embolization are subjected to inherent biases toward those judged to be more likely to benefit.^{29,​ 30} Therefore, in carefully selected patients with large convexity meningiomas undergoing surgery, preoperative embolization may be considered.

23.10 Radiotherapy

Radiotherapy has not traditionally been considered a primary treatment modality for convexity meningiomas. However, as the indication and utilization of radiosurgery expanded over the last few decades, radiosurgery has been considered a potential form of primary treatment for convexity meningiomas. Kondziolka et al³¹ published their experience of treating convexity meningiomas less than 3.5 cm in size using the Leksell Gamma Knife in patients who refused other treatment options, and in patients with concomitant medical illness or of advanced age, and also in patients with symptomatic lesions located in areas of higher surgical risk. They reported a tumor control rate of 92% for their cohort who had primary radiosurgery, with a 6.2% incidence of morbidity. The effectiveness and risk of radiosurgery is therefore similar to the efficacy and morbidity of surgical resection and should be considered for patients who present with a meningioma that is increasing in size and who refuse surgery or are medically unfit for surgery.

In a review by Kaur et al,³² adjuvant radiotherapy was found to improve progression-free survival and overall survival for anaplastic meningiomas, but not atypical meningiomas where a good surgical resection had been achieved. Postoperative radiotherapy may be considered for atypical meningioma with subtotal resection.

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