Expression of smooth muscle proteins in cavernous and arteriovenous malformations

Cavernous malformations (CVMs) and arteriovenous malformations (AVMs) were immunostained for three smooth muscle cell (SMC)-specific protein markers (smooth muscle α-actin, SM1 and SM2). Smooth muscle α-actin, a widely used marker of SMCs, is reportedly one of the earliest proteins expressed during differentiation of SMCs and expressed in some kinds of mesoderm-derived cells. In contrast, SM1, an isoform of myosin heavy chain (MHC), is detected only in SMCs. SM2 is another MHC isoform and expressed in the contractile phenotype of SMC. All 14 intraaxial CVMs were positive for smooth muscle α-actin, but SM1 was detected in only three of them and SM2 was not found. Their staining pattern resembled that of normal intraparenchymal and pial veins. All 15 cerebral AVMs and 5 out of 6 extraaxial CVMs from the cavernous sinus, orbit and scalp were positive for all three markers, as were the normal cerebral arteries. The venous components of AVMs, as well as the arterial components, expressed SM2, and were different from normal veins in the brain and intraaxial CVMs. This study shows that the histological analysis using the three markers for SMC is useful to differentiate intraaxial CVM from AVM and extraaxial CVMs.