Capillary hemangioblastoma: histogenesis of stromal cells

Pathology of the Nervous System in Von Hippel-Lindau Disease

Von Hippel-Lindau (VHL) disease is a tumor syndrome that frequently involves the central nervous system (CNS). It is caused by germline mutation of the VHL gene. Subsequent VHL inactivation in selected cells is followed by numerous well-characterized molecular consequences, in particular, activation and stabilization of hypoxia-inducible factors HIF1 and HIF2. The link between VHL gene inactivation and tumorigenesis remains poorly understood. Hemangioblastomas are the most common manifestation in the CNS; however, CNS invasion by VHL disease-associated endolymphatic sac tumors or metastatic renal cancer also occur, and their differentiation from primary hemangioblastoma may be challenging. Finally, in this review, we present recent morphologic insights on the developmental concept of VHL tumorigenesis which is best explained by pathologic persistence of temporary embryonic progenitor cells.

Nervous system involvement in von Hippel-Lindau disease: pathology and mechanisms

Patients with von Hippel-Lindau disease carry a germline mutation of the Von Hippel-Lindau (VHL) tumor-suppressor gene. We discuss the molecular consequences of loss of VHL gene function and their impact on the nervous system. Dysfunction of the VHL protein causes accumulation and activation of hypoxia inducible factor (HIF) which can be demonstrated in earliest stages of tumorigenesis and is followed by expression of VEGF, erythropoietin, nitric oxide synthase and glucose transporter 1 in VHL-deficient tumor cells. HIF-independent functions of VHL, epigenetic inactivation of VHL, pVHL proteostasis, and links between loss of VHL function and developmental arrest are also described. A most intriguing feature in VHL disease is the occurrence of primary hemangioblastic tumors in the nervous system, the origin of which has not yet been entirely clarified, and current hypotheses are discussed. Endolymphatic sac tumors may extend into the brain, but originally arise from proliferation of endolymphatic duct/sac epithelium; the exact nature of the proliferating epithelial cell, however, also has remained unclear, as well as the question why tumors almost consistently develop in the intraosseous portion of the endolymphatic sac/duct only. The epitheloid clear cell morphology of both advanced hemangioblastoma and renal clear cell carcinoma can make the differential diagnosis challenging, recent developments in immunohistochemical differentiation are discussed. Finally, metastasis to brain may not only be caused by renal carcinoma, but may derive from VHL disease-associated pheochromocytoma/paraganglioma, or pancreatic neuroendocrine tumor.

Primary Capillary Hemangioblastoma of Bone: Report of a Case Arising in the Sacrum

Capillary hemangioblastoma (CHB) is a benign, highly vascularized tumor that generally occurs in the central nervous system either in the setting of von Hippel-Lindau (VHL) disease or, more often, as a solitary sporadic lesion that is increasingly recognized in extraneural sites. We present the case of a 72-year-old woman with low back pain and a well-demarcated lytic lesion of the sacrum, which at histological and ultrastructural examination was indistinguishable from central nervous system CHB. The patient had no signs of VHL disease and died of another cause with no evidence of disease 57 months after curettage of the lesion. To our knowledge, this is the second case of CHB reported to occur in bone.

Extraneural hemangioblastoma: a report of 5 cases

Hemangioblastoma is a morphologically distinctive tumor that can occur sporadically or in association with von Hippel-Lindau disease, and which involves the central nervous system in the majority of the cases. Rare occurrences of hemangioblastoma in peripheral nerves and extraneural tissues have been reported. The histogenesis of this tumor remains uncertain. Various cell lineages such as vascular, glial, neural, fibrohistiocytic, and smooth muscle/myofibroblastic have been proposed for the so-called stromal cells, which are thought to represent the neoplastic component of these lesions. We report on 5 cases of hemangioblastoma arising in extraneural tissues. Two of the tumors were located in the presacral region, and one each in the maxilla, kidney, and adrenal glands. All 5 cases were morphologically indistinguishable from central nervous system hemangioblastoma. The existence of these cases suggests that the "stromal" cells of hemangioblastoma can demonstrate a variety of mature specific lineages, such as smooth muscle/myofibroblastic, or neuroendocrine, depending on the location and possibly the microenvironment.

Central nervous system capillary haemangioblastoma: the pathologist's viewpoint

Haemangioblastomas are rare neoplasms of uncertain histogenesis. They represent 1.5-2.5% of intracranial tumours. While the cerebellum is by far the most frequent site, these lesions also tend to occur in the medulla and spinal cord. Most haemangioblastomas are sporadic but up to one quarter are associated with Von Hippel-Lindau disease (VHL). Although a fairly good number of haemangioblastomas were reported, a lack of side-by-side analysis of these reports has resulted in tentative conclusions that merely offer a first glimpse at their clinicopathologic diversity and histogenesis. To remedy this issue, this study presents a literature review concerning these lesions. Medline literature including both relevant monographs and clinicopathological case series. Haemangioblastomas occur either as a part of VHL disease (25-30%, inherited mutation of VHL gene on 3p25-26 chromosome) or as sporadic tumours (often with somatic mutation of VHL gene). They have diverse clinicopathologic presentations with cerebellar lesions having a better prognosis than their brainstem counterparts. Immunostaining is important for separation of haemangioblastomas from other tumours with similar histology. The rich vascularity of haemangioblastomas is due to overexpression of vascular endothelial growth factors. Moreover, 'stromal' cells represent the neoplastic cells of haemangioblastomas and are capable of forming blood islands with extramedullary haematopoiesis.

Histologic and histogenetic investigations of intracranial hemangioblastomas

BACKGROUND

The aim of this study was to elucidate the histologic characteristics and the histogenesis of intracranial HBs.

METHODS

Specimens from 40 patients with HBs were verified surgically and pathologically at the Huashan Hospital Department of Neurosurgery (Fudan University, Shanghai, China). All sections were immunohistochemically stained. In addition, fresh specimens were examined by electron microscopy in 3 cases and cells were cultured in 10.

RESULTS

Hemangioblastomas were composed of endothelial cells, pericytes, and stromal cells. Vimentin was expressed in all 3 cell types of HB. CD34 was expressed in endothelial cells, and SMA was expressed in pericytes. Telomerase was expressed in stromal cells. Chromogranin A, CD68, and CD117 showed a negative reaction in HBs. Vascular endothelial growth factor showed a positive reaction in stromal cells, and Flt-1 showed a positive reaction in endothelial cells. There was no difference in immunohistochemical staining between specimens from cystic HBs and those from solid HBs. Three cell types had individual ultrastructural characteristics. Stromal cells represented a heterogeneity of abnormally differentiating mesenchymal cells in cell culture.

CONCLUSIONS

Hemangioblastomas may originate from the mesenchyme. Stromal cells are the real tumor components of HBs although they represent a heterogeneity.

Hemangioblastomas share protein expression with embryonal hemangioblast progenitor cell

Hemangioblastomas are central nervous system (CNS) tumors of unknown histogenesis, which can occur sporadically or in von Hippel-Lindau disease. Hemangioblastomas are composed of neoplastic "stromal" cells of unknown origin, accompanied by intensive reactive angiogenesis. Failure to specify the cytologic origin of the stromal cell has precluded the development of nonsurgical therapies and limits understanding of its basic biology. We report that the stromal cells express proteins (Scl, brachyury, Csf-1R, Gata-1, Flk-1, and Tie-2) that characterize embryonic progenitor cells with hemangioblastic differentiation potential and conclude that embryonic progenitors with hemangioblast potential represent a possible cytologic equivalent of the stromal cell. We also identified a new autocrine/paracrine stimulatory loop between the receptor Tie-2 and the hypoxia-inducible factor target Ang-1, which, combined with previous observations, suggests that a variety of autocrine loops may be initiated in hemangioblastomas, depending on the differentiation status of the tumor cells and the extent of HIF downstream activation. Finally, the consistent identification of Scl in the stromal cells may help explain the unique and characteristic topographical distribution of hemangioblastomas within the CNS.

Stromal cells in hemangioblastoma: neuroectodermal differentiation and morphological similarities to ependymoma

The histogenesis of stromal cells in hemangioblastoma is inconclusive despite a long-term controversy. An immunohistochemical and ultrastructural study was conducted for 17 cases of cerebellar hemangioblastoma. A wide range of immunohistological markers, targeting epithelial, mesenchymal, endothelial and neuroectodermal tissues, was used. In all cases, the microscopic hallmark characterizing hemangioblastomas, that is, lipid-containing stromal cells and a fine capillary network, known as a reticular variant, was noted. Stromal cells showed a variable immunoreactivity for neuroectodermal markers, such as S-100 protein, CD56, CD57, CD99, and neuron-specific enolase. This result, in conjunction with the absence of immunoreactivity for epithelial, mesenchymal, and endothelial markers, likely suggests neuroectodermal differentiation of stromal cells. In three cases, another component, known as a cellular variant, where epithelioid tumor cells were arranged in nests encircled by capillaries and/or in pseudorosette-like structures, was noted. Glial fibrillary acidic protein-immunoreactivity, which was totally absent in cases only showing the reticular pattern, was noted in two of them, suggesting a distinctive sign of glial differentiation in a proportion of hemangioblastomas. Ultrastructurally, microvilli-like projections in intracytoplasmic vacuoles were demonstrated in stromal cells. This result, taken together with the neuroectodermal hypothesis of stromal cells, suggests that hemangioblastomas may occasionally exhibit morphological similarities to ependymomas.

Retroperitoneal peripheral hemangioblastoma: a case report and review of the literature

Central nervous system hemangioblastomas are uncommon tumors of controversial etiology that are usually found in the posterior fossa of the cranial cavity, retina, and spinal cord. Peripheral involvement is rare; only isolated case reports have been identified. We report an unusual case of hemangioblastoma involving the retroperitoneum. A 47-year-old African-American man presented with polycythemia on routine laboratory testing. Computed tomography revealed a large retroperitoneal mass near the pancreas, in a left suprarenal location, without adrenal involvement and without attachment to a nerve. Although hemangioblastoma may be associated with the von Hippel-Lindau syndrome, this patient did not have any of the stigmata of this disease. The histologic features included a highly vascular tumor with cellular areas composed of plump, pleomorphic spindled and epithelioid (stromal) cells with variable cytoplasmic lipid vacuoles and hypocellular areas with inflammatory cells and collagenous fibrils. Immunohistochemical staining showed that the tumor (stromal) cells were positive for vimentin, calponin, S-100 protein, neuron-specific enolase, and CD57 and negative for glial fibrillary acidic protein, cytokeratins, epithelial membrane antigen, CD34, HMB-45, desmin, and the actins. These morphologic and immunohistochemical findings are consistent with hemangioblastoma. To our knowledge this is the first reported case of a hemangioblastoma in this location. Based on this case we conclude that hemangioblastoma may occur in the retroperitoneum and outside of the central nervous system in a patient without von Hippel-Lindau syndrome. The immunoprofile of this case suggests that hemangioblastomas are mesenchymal neoplasms exhibiting both neural and myofibroblastic differentiation.

Angiogenic histogenesis of stromal cells in hemangioblastoma: ultrastructural and immunohistochemical study

Controversy regarding the origin of characteristic stromal cells (SC) is responsible for the placement of hemangioblastoma as a single entity in the category of "tumors of uncertain histogenesis" in the current WHO classification of brain tumors. This subclassification of hemangioblastoma is, to a large extent, a consequence of a remarkable antigenic heterogeneity of SC demonstrated in many, often contradictory immunohistochemical studies. In contrast, most of the electron microscopic studies demonstrated a number of features indicating angiogenic nature of SC and, therefore, hemangioblastoma. This study reevaluated the histogenesis of SC, applying immunohistochemistry as well as electron microscopy and immunoelectron microscopy. Immunohistochemical studies confirmed most of the previous results indicating a very frequent expression of vimentin, S-100 protein, neuron-specific enolase, and cytokeratins. SC were less commonly immunoreactive for desmin, factor XIIIa, and Ricinus communis lectin receptors, and only occasionally for factor VIII and Ulex europeus lectin. They were negative for other markers of endothelial, neuronal, glial, neuroendocrine, and smooth muscle differentiation. Approximately 1% of SC showed Ki67 immunoreactivity, indicating their slight proliferative activity, consistent with the benign nature of the tumor. In contrast to the inconclusive results of the immunohistochemistry, electron microscopy demonstrated a clear relationship of SC to endothelial cells, smooth muscle cells, and pericytes. Occasional SC were found within the vascular lumina. SC often showed intracellular caveolae consistent with the formation of early capillary lumina. Moreover, occasional SC contained small Weibel-Palade bodies positive for factor VIII in immunoelectron microscopy. SC represent a heterogeneous population of abnormally differentiating mesenchymal cells of angiogenic lineage, with some morphological features of endothelium, pericytes, and smooth muscle cells. Occurrence of SC in hemangioblastoma could be related to a limited ability of angioformative stromal cells to develop an architecture of capillary lumina integrated with the vascular network of the tumor. Hemangioblastoma should be reclassified and included together with other vascular tumors of the central nervous system.

Intracranial suprasellar angiolipoma: ultrastructural and immunohistochemical features

The authors present ultrastructural and immunohistochemical characteristics of an intracranial suprasellar tumor displaying features of cavernous angioma with islets of adipose tissue. Electron microscopy revealed thin-walled vessels separated by a loose collagenous stroma containing nests of mature adipocytes as well as fibroblasts, myofibroblasts, mast cells, and a few macrophages. Intracytoplasmic lipid droplets were also identified in scattered pericytes and smooth muscle cells of vascular walls and in the transitional cells resembling smooth muscle cells and adipocytes. Many adipose tissue cells were positive for S-100 protein with polyclonal antibodies. Other lipidized tumor cells were immunoreactive for some or all of the following: smooth muscle-specific actin, factor XIIIa, vimentin, and, occasionally, for desmin. Ultrastructure and immunohistochemistry indicate that in addition to typical adipocytes, lipidized cells of another nature contribute to the characteristic appearance of the adipose tissue component of angiolipoma.