In 1845, Toynbee first reported a case of cavernous hemangioma of the skull, and this condition was defined by Rowbotham from the histological point of view until 1924 . Most reviews of PICH of the skull concern the parietal and frontal bone. Only 45 cases referred to the orbital bone, but they were all single lesions described in a review by Madge et al. . Therefore, cases of multiple lesions are rare. So far, only 10 cases of multiple lesions have been reported (including this case) . Skull PICHs are characterized by protrusion into the external plate of the skull, and the cases in which these tumors grow into the internal skull are rare. To date, only three cases have been reported (including this case) [4, 5].
Radiography of the skull is the most useful method to identify PICHs, whose typical features are a “honeycomb” or “sunray” pattern . However, in our case, the lesions in the parietal bone on plain film were atypical, showing osteolysis and cortical bone expansion. This appearance has been reported in cases of radiographically occult orbital lesions. Owing to the complexity of the orbit, plain radiographs are occasionally misleading, and orbital CT is recommended. With computed tomograms, one can visualize the honeycomb pattern of boney trabeculae and design an operation for complete resection . MR imaging can clearly show the relationship between the tumor and brain tissue. T1- and T2-weighted MR have different performances. T1-weighted MR is mainly influenced by fat content, so it is nonhomogeneously isointense and generally resembles the gray matter, whereas the T2-weighted MR is hyperintense and may be associated with water and slow-flowing blood in the tumor. In our case, due to the small size of the lesions in the parietal bone, these characteristics were not evident. We did observe T1- and T2- hypointense signals at the center of the orbital lesions, and both lesions enhanced, consistent with prior reports [4, 6].
There are two histological classifications of PICH: sinus and capillary. Most PICHs of the spinal canal are classified as sinus, and many PICHs of the skull are classified as capillary . Madge et al. summarized 45 cases of orbital PICHs, of which 80 percent were sinus, 17 percent were capillary, and 3 percent were mixed types . Sinus and capillary PICHs have different characteristics. Capillary hemangiomas lack fibrous septa and have smaller vascular lumens. The endothelial cells are often small and lack mitotic activity. In contrast, sinus hemangiomas tend to relapse, and are composed of groups of large, dilated blood vessels are separated by fibrous tissue. Surgery for cavernous hemangiomas is likely to be complicated by hemorrhage .
The present case should be distinguished from multiple tumors that penetrate into the internal skull. Because approximately 70 percent of meningiomas have the dural tail sign and because the other MRI features of this case were similar to those of meningiomas, we considered this to be the disease before the operation . In this case, the CT bone window was atypical for meningioma, however. The other differential diagnoses included hemangiopericytoma, osteosarcoma, metastases, and inflammatory granuloma .
Total surgical resection is the major treatment of skull PICH. This surgical procedure has the benefits of low blood loss during the operation and a low recurrence rate after the operation . Resection should include a 1-cm width of the normal skull around the lesions. For frequently occurring skull PICHs, it is controversial whether the resection should be conducted in conjunction with the resection of the asymptomatic lesions or not. Among the nine cases of multiple PICHs previously reported, six cases were treated with total resection, and in one case the asymptomatic lesions were removed. Naama et al.  hypothesized that asymptomatic lesions were observed because PICH grows slowly, and its symptoms often appear several years later. However, cranial tumors can cause neurological symptoms and harbor a small risk of hemorrhage . We planned on an operative resection of meningiomas, but concluded that gross total resection would have been our goal had we known the diagnosis a priori.
Other reported treatments include curettage and radiotherapy. Curettage may lead to serious bleeding during the operation and recurrence after the operation . Radiotherapy is only able to prevent the tumor from growing, and cannot eradicate the lesions. In addition, malignant transformation of PICHs after radiotherapy has been reported [6, 11]. Therefore, these two methods should only be applied in cases in which it is not completely safe to perform removal. Although PICH is rare, it should be considered in the identification of lesions occupying the skull space. For frequently occurring cases with the dural tail sign, surgery should strive to remove all of the lesions. After several years of development, asymptomatic lesions may grow into the internal skull, leading to symptoms of the nervous system.