FINAL DIAGNOSIS: MENINGIOMA AND MENINGIOANGIOMATOSIS
Meningioangiomatosis (MA) is a rare benign intracortical plaque-like proliferation of meningothelial cells, microvasculature and fibroblast-like cells. Other findings include degenerative calcifications, fibrocartilage formation or ossification. The adjacent cortex may show dense gliosis and neurofibrillary tangles. These lesions may occur sporadically or in the setting of neurofibromatosis type 2 (NF-2) (3,10,15). In the largest series reviewed, sporadic cases of MA were found to occur more frequently than those associated with NF-2 in a ratio of 4:1(16). Sporadic MA is usually a solitary lesion that occurs in children and young adults who present with a history of seizures or persistent headache. NF-2 associated MA are more frequently multiple and asymptomatic, and are diagnosed usually at autopsy (8,10). The main differential consideration is brain invasive meningioma.
The histogenesis of MA remains uncertain. As a result of an inconstant immunostaining profile, the histogenesis of MA has been variably suggested as meningeal, pericytic or perivascular neural plexus (4,16). However, ultrastructural findings of desmosomes and interdigitating cell membranes in the fibroblast-like cells of some MA lesions are suggestive of meningothelial differentiation (4,9). Paulus and colleagues (13) in an immunohistochemical analysis of cells and collagen types present in MA, have concluded that the fibroblast-like cells are probably of meningothelial origin rather than of glial, Schwann cell, endothelial or smooth muscle origin. In our case, staining for EMA, a marker for arachnoid cap cells, is focally positive in the cortical perivascular whorls. Although EMA positive staining has been reported previously in MA (6), it is not a consistent characteristic of the lesion (16).
The pathogenesis of MA is undetermined as well. There are three main hypotheses (8): a) MA is a hamartoma that undergoes degenerative changes. b) MA is a cortical vascular malformation that induces proliferation of cells from vessel walls or pluripotent arachnoid cap cells in the Virchow-Robin spaces. c) MA represents direct invasion of brain parenchyma by a leptomeningeal-based meningioma. Regardless of the pathogenesis, MA is, at most, a slow growing lesion. MA generally demonstrates a low Mib-1 index as in this case (14). Neurofibrillary tangles (NFTs) are not uncommon in cases of MA (6,7,13). NFTs may be a degenerative phenomenon rather than an intrinsic component of the lesion (7). Furthermore, in contrast to invasive atypical or malignant meningiomas, MA generally does not recur.
In rare instances, MA may present with an associated overlying meningioma. None of 9 such cases reported in the literature, including the present case, are known to be associated with NF-2 (1,2,6,11,12,17). The age distribution of MA associated with meningioma is the same as isolated MA. Whether pediatric invasive sclerosing meningiomas (5), a histologically similar entity with a good prognosis, is MA with a predominantly sclerotic background or a distinct entity remains to be determined.
It is important to recognize MA when it is associated with an overlying meningioma because of the possibility of being misinterpreted as an invasive atypical or malignant meningioma. In contrast to atypical or malignant meningioma, MA is unlikely to recur and does not require adjunctive therapy such as radiation. Features such as mitoses, necrosis, and sheeting would support the diagnosis of an aggressive meningioma. A histologically bland invasive meningioma may be a potentially difficult diagnostic dilemma. However, the presence of neurofibrillary tangles and profuse cortical microvasculature would support a diagnosis of meningioangiomatosis.
Contributed by Iezza G, Loh C, Lanman TH, Yong WH