**2. Classification of the recurrences**

According to their topography on the post-contrast magnetic resonance imaging (MRI) and surgical findings, the recurrences of meningiomas may be classified in 4 types [28]:


Local type 1 is the most frequent regrowth pattern. It may occur after resection of Simpson grades 2 to 4; the tumor may growth both intradurally and at the bone. The recurrence may involve from a variable portion to the whole initial dural attachment and may extend to the contiguous previously normal dura.

Peripheral type 2 recurrences may be observed after initial resection of grade 1, but also of grade II when the dural attachment was carefully and extensively coagulated. The recurrence may involve a variable dural portion contiguous to the initial attachment and may often extend to it. In cases with larger recurrences the site of regrowth (local versus peripheral) is difficult to be defined.

Multicentric type 3 recurrences are characterized by tumor nodules or mass both at initial dural attachment or contiguous dura and in distal dural regions where no tumor nodules nor dural enhancement were visible on the magnetic resonance imaging at initial surgery. In this type the dura mater between local-peripheral and distal recurrent nodules seems to be normal.

Diffuse type 4 recurrences show multiple nodules of tumor regrowth even in very distal regions, with variable infiltration of the interposed dura and bone.

The above discussed patterns of recurrence suggest that multicentric and diffuse recurrences are two phases of the same pathological conditions.

## **3. Pathological origin of the multicentric-diffuse recurrences**

The pathological mechanisms responsible for meningioma recurrence in distal dural regions are not well defined and deserve to be discussed.

The concept of regional multicentricity of meningiomas is known since about 35 years. Borovich and Doron [29] demonstrated in convexity meningiomas small tumor nodules as well as intradural clusters of tumor cells in the dural specimens taken up to 3 cm from the tumor. Qi et al. [30] found tumor invasion in 88% of dura adjacent to convexity meningioma up to 2,5 cm from the tumor origin. These observations may explain some "unexpected relapses" after an apparent complete resection (Simpson grade 1) of convexity meningiomas [29] and the frequent peripheral recurrences at the dura surrounding the initial attachment after resection od Simpson grades 1 and 2 in all locations.

*Topographic Distribution of Intracranial Meningioma's Recurrences: Localized Versus Diffuse… DOI: http://dx.doi.org/10.5772/intechopen.97120*

These pathological findings support the concept of a wide dural excision 2-3 cm beyond the tumor base (grade zero resection), which was suggested for convexity [31] and falx meningiomas [32].

Mooney et al. [32] suggest that in the falcine meningiomas the tumor cells may spread from the site of origin to other falx regions between the two dural leaflets of the falx. However, this pattern of diffusion of the tumor cells cannot explain the very distant recurrences from other locations. For multiple meningiomas some studies [33, 34] have suggested that they may arise from a single progenitor cell and could then spread through the subarachnoid space. A similar mechanism may also be advocated for distant recurrences.

However, it is more like that multicentric-diffuse recurrences represent the progressive growth of multiple distant dural nodules with different growth potential. In this way the meningioma may be considered, at least in several cases, a diffuse disease of the meninges than a localized tumor.
