Meningioma and intracranial hemangiopericytoma. A comparative electron microscopic study

Recent Experience in the Management of Meningeal Hemangiopericytomas

Although the histogenesis of meningeal hemangiopericytomas (HMP) remains controversial, both biological and clinical evidence seems to identify these neoplasms as a separate entity with respect to meningiomas. In order to assess the current prognosis of HMP we reviewed our personal experience limited to the last decade (1986-1995): during this period 7 patients (4M, 3F) were treated by surgery alone or surgery combined with postoperative radiotherapy. In spite of meticulous attempts at radical resection, the tumors recurred in all but two cases with a mean interval of 85 months, and a total of 18 operations were performed (2.57/patient; range 1-4). Massive intratumoral hemorrhage determined acute deterioration and required emergency surgery in two cases while in one patient diffuse visceral metastases were discovered at autopsy. Five patients are still alive at follow-up but only 2 of them are in good neurological conditions and without evidence of disease. These results are similar to those reported in other series. In view of our results we conclude that intracranial hemangiopericytomas still have a dismal prognosis. Advances in neuroimaging, neuroanesthesia, microneurosurgery and adjuvant therapy do not seem to have significantly affected the recurrence rate, quality of life and mortality.

Intracranial meningeal hemangiopericytoma metastatic to the scapula

Meningeal hemangiopericytomas are rare vascular tumors that have a propensity for recurrence and metastasis. Intracranial hemangiopericytomas are rare vascular tumors. They account for 0.5% of primary central nervous system tumors and 2% of meningiomas. Unlike usual benign meningiomas, which rarely metastasize extracranially, meningeal hemangiopericytoma has a high rate of local recurrence and distant metastasis. The treatment paradigms for hemangiopericytomas and meningiomas differ based on their biological behaviors. Hemangiopericytomas have higher rates of recurrence and metastasis compared with meningiomas. Intracranial meningeal hemangiopericytoma is characterized by clinically repeated local recurrences at the primary site. Bone, liver, lung, central nervous system, and abdominal cavity are the most commonly reported sites of metastasis in hemangiopericytomas.This article describes a case of bone metastasis with extensive involvement of the scapula from intracranial hemangiopericytoma. Bone metastasis can be seen in a relatively late phase of the disease, with metastasis to other organs. Although radiation therapy is effective in controlling pain from bone metastases in unresectable disease and those with extensive visceral metastases, aggressive local surgical control of a solitary bone metastasis may be an option for patients with limited distant disease. The diagnosis may be initially confused with clear cell meningioma and benign meningiomas. The management of bone metastasis is not well reported in the orthopedic literature.

Unusual tumors of the posterior fossa skull base

Five unusual cases of posterior skull base tumors were treated through different skull base approaches. Two or more staged operations were required to achieve total or near-total excision and decompression of two extensive tumors. Total excision of an extensive en plaque meningioma of the foramen magnum that encircled the brain stem and cervical spinal cord could not be achieved through the extreme lateral and suboccipital craniectomy approach. However, the vital structures were decompressed and the patient's postoperative morbidity was acceptable. An extended middle fossa approach was required to excise a hemangiopericytoma of the middle and posterior fossae in a 12-year-old. Extension of the tumor into the posterior fossa precluded a retromastoid approach because the mass draped the lower cranial nerves posteriorly. Two men had undifferentiated adenocarcinomas involving the jugular foramen and middle to posterior fossa, respectively. The origin of one was renal in a 37-year-old man. A 63-year-old man survived 1.5 years after a good decompression of his extensive tumor and irradiation. The histological diagnosis of paraganglioma of the occipital bone was a surprise in a 25-year-old man with pure bony involvement. These cases indicate that the appropriate selection of skull base approaches and their combination can provide the needed access to achieve adequate excision or decompression of masses located in challenging anatomical regions of the skull base. Furthermore, good surgical excision improves palliation in radioresistant metastatic tumors of the skull base.

Anaplastic meningioma versus meningeal hemangiopericytoma: Immunohistochemical and genetic markers

Anaplastic meningiomas (MIIIs) and meningeal hemangiopericytomas (HPCs) display significant morphologic and immunohistochemical overlap, including occasional cases of otherwise classic HPC with focal epithelial membrane antigen (EMA) positivity. The availability of several new biomarkers prompted us to examine the potential diagnostic roles of ancillary immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) studies. From the archival university neuropathology and consult files of 1 of the authors (A.P.), 19 meningeal HPCs and 19 MIIIs were retrieved for further study. IHC was performed by using EMA, CAM 5.2, CD99, Bcl-2, claudin-1 and Factor XIIIa (FXIIIa) antibodies. FISH was performed with NF2, 4.1B (DAL-1), chromosome 1p32, and 14q32 probes. HPCs showed strong CD99 (85% of cases), strong bcl-2 (86%), focal EMA (33%), focal claudin-1 (13%), and scattered individual cell FXIIIa (100%) positivity. MIIIs showed strong EMA (89%), strong claudin-1 (54%), weak or focal CD99 (15%), weak or focal bcl-2 (31%), and individual cell FXIIIa (84%) positivity. Focal CAM 5.2 expression was seen in 26% of HPCs and 15% of MIIIs. Deletions were extremely common in MIIIs: 1p (94%), 14q (67%), NF2 (100%), and 4.1B (67%). HPCs showed no 14q or 4.1B deletions, with 1 case each of 1p and NF2 deletions (6%). The sensitivities and specificities of the 3 most useful IHC markers (EMA, CD99, bcl-2) were 85%-89% and 67%-84%, respectively. The sensitivity and specificity of claudin-1 for MIII were 54% and 86%, respectively. The specificity and positive predictive value of combined CD99 and bcl-2 expression for the diagnosis of HPC was 95%. The sensitivities of individual genetic markers were 67%-100%, with specificities of 94%-100%. Our 3 conclusions were as follows: (1) EMA, CD99, bcl-2, and claudin-1 IHC and 1p, 14q, NF2, and 4.1B FISH are particularly useful for distinguishing anaplastic meningiomas from meningeal HPCs. (2) Focal EMA expression does not preclude a diagnosis of HPC. (3) The characteristic FXIIIa staining pattern reported for HPC also is encountered frequently in anaplastic meningiomas and therefore is nonspecific in this diagnostic setting.

Hemorrhage in cerebral metastasis from angiosarcoma of the heart: case report

The purpose of this article is to describe the clinical and pathological features of metastatic angiosarcoma in the central nervous system. Only a few cases of cerebral metastasis from angiosarcoma of the heart have been recorded in the literature; particularly related to intracerebral hemorrhage. A case of secondary cerebral angiosarcoma of the heart in a 33 years old man is presented. The initial symptoms were headache, vomiting, lethargy and aphasia. There was a mass in the left temporal lobe with hemorrhage and edema on the computerized tomography (CT). After 24 hours the neurological status worsened and another CT scan showed rebleeding on the tumor area. He underwent an emergency craniotomy but died two days after. Considering the longer survival of sarcoma patients with new modalities of treatment, the incidence of brain metastasis may increase, demanding a better preventive and more aggressive approach. Besides, due to the hemorrhagic nature of such lesions, we suggest the immediate surgery to prevent a fast and lethal evolution because rebleeding.

Recurrence in meningeal hemangiopericytomas

BACKGROUND

Meningeal hemangiopericytomas are more aggressive than typical meningiomas, with a high rate of recurrence and distant metastases. The question of whether a correlation exists between prognosis and histologic features remains controversial.

CASE DESCRIPTION

We report two cases of recurrent meningeal hemangiopericytomas. Although local growth control of the tumor was obtained by tumor removal and irradiation in a 38-year-old male patient (Case 1) with a recurrent tentorial tumor, the tumor disseminated and metastasized extracranially within a short period after treatment, leading to rapid deterioration. Another 38-year-old female patient (Case 2) with a recurrent orbital tumor had a favorable outcome after tumor removal. The Ki-67 proliferative index using the MIB-1 monoclonal antibody increased as the tumor recurred in Case 1 (2.5%, 7.9%, and 15.7%), but did not change between primary and recurrent tumors of Case 2 (4.2%, 3.1%). Immunostaining for p53 protein in Case 1 was negative at the first resection, and became positive at the second and third resections, whereas in Case 2, it was negative in both the primary and recurrent tumors.

CONCLUSIONS

Our results suggest that p53 protein accumulation with a high proliferative potential is a useful marker to estimate malignant progression in meningeal hemangiopericytomas.

The immunophenotypic spectrum of meningeal hemangiopericytoma: a comparison with fibrous meningioma and solitary fibrous tumor of meninges

Despite controversy regarding its histogenesis, meningeal hemangiopericytoma (HPC) is a well-defined clinicopathologic entity exhibiting high rates of recurrence and late extracranial metastasis. It must be distinguished from several benign neoplasms, particularly fibrous meningioma (FM) and solitary fibrous tumor (SFT). To determine the immunoprofile of HPC, we studied 27 meningeal examples, including 13 low-grade and 14 high-grade tumors. For comparison, 20 FMs and eight SFTs of the meninges were also evaluated. The immunotype of HPC included vimentin (85%), factor XIIIa (78%) in individual scattered cells, Leu-7 (70%), and CD34 (33%) in a weak, patchy pattern. Focal desmin and cytokeratin positivity was only occasionally encountered (20% each). The SFT shared a similar immunophenotype, except that CD34 expression (100%) was characteristically strong and diffuse. The FM characteristically expressed epithelial membrane antibody (EMA) (80%) and S-100 protein (80%); CD34 reactivity (60%) was patchy and weak. Both within and among all three tumor types, MIB-1 labeling indices varied widely. Specifically, they were unrelated to tumor grade in HPC. Significant reactivity for p53 protein was detected in 52% of HPCs, 17% of SFTs, and 5% of FMs. Meningeal HPC exhibits a distinct antigenic profile, one enabling the exclusion of other entities in nearly all cases. The rare expression of desmin or cytokeratin in HPC suggests either the occurrence of divergent differentiation or, less likely, the possibility that its distinctive morphology is but a phenotype shared by several types of meningeal sarcoma.

Primary angiosarcoma of the brain: case report

A 41-year-old patient with a primary angiosarcoma of the brain is reported. The tumor was located in the left parietal lobe and was radically removed. The diagnosis of angiosarcoma was established by immunohistochemistry. The patient was postoperatively treated with adjuvant chemotherapy and then radiation therapy. After 41 months, she was in excellent clinical and neurological condition without any sign of recurrence.

Hemangiopericytoma of the temporal bone presenting as a retroauricular mass

An unusual case of a hemangiopericytoma arising from the temporal bone is presented. The patient was noted to have a postauricular mass and was neurologically asymptomatic. A preoperative magnetic resonance image and an angiogram revealed the tumor to be highly vascular. Preoperative embolization facilitated the surgical removal of the tumor by rendering it avascular. Current therapy consists of radical resection of the tumor with postoperative radiation therapy. Patients must be monitored carefully for local recurrence and systemic metastasis.

Meningeal hemangiopericytoma of the posterior fossa and thoracic spinal epidural space: case report

The rare combination of spinal and intracranial meningeal hemangiopericytomas in the same patient is reported. The coexistence of cerebral and spinal meningiomas of all histological subtypes is distinctly uncommon with only nine cases found in the literature.

Hemangiopericytoma of the central nervous system: a review of 94 cases

Ninety-four cases of central nervous system hemangiopericytoma (CNS-HPC) are reported. Hemangiopericytoma was found more commonly in men than in women. The mean age at diagnosis was 40.9 years for men and 47 years for women. The tumor was found throughout the entire CNS, usually superficially and closely related to the meninges. Based on multiple histologic variables, the original tumors were divided into differentiated (n = 67) and anaplastic (n = 27). Anaplastic HPC was characterized by the presence of necrosis and/or greater than five mitoses per ten 400x microscopic fields, and at least two of the following microscopic features: hemorrhage, moderate to high nuclear atypia, and moderate to high cellularity. For those patients known to be dead, median survival time was 144 months for differentiated HPC and 62 months for anaplastic HPC. Fifty-seven (60.6%) patients had one or more recurrences and metastasis developed in 22 (23.4%). Thirty-five of 56 patients with differentiated HPC had recurrence, while 22 of 26 patients with anaplastic HPC had recurrence. Bone, liver, lung, central nervous system, and abdominal cavity were the most common sites of metastasis. Postoperative radiotherapy and/or chemotherapy were significantly associated with increased patient survival time.

So-called minute chemodectoma of the lung. An electron microscopic and immunohistochemical study

So-called minute pulmonary chemodectoma is a curious, small lung tumour found mainly in women. The nature and origin of the proliferating cells are still obscure. In the first report on the tumour, the component cells were described as resembling chemoreceptor cells and the tumour was named chemodectoma. However, electron microscopic studies of the tumour have revealed no evidence of neuronal characteristics and have shown a close resemblance to meningothelial cells. In this study, the electron microscopic findings were similar to those previously reported but in one of the two cases, tumour cells were filled with abundant cytofilaments, giving them an occasional dense, patch-like appearance. Immunostaining for myosin and vimentin was positive in all tumour cells, but epithelial membrane antigen staining was not seen. These findings indicate that the tumour might have its origin from muscle cells.

Histogenesis of intracranial haemangiopericytoma and haemangioblastoma. An immunohistochemical study

An immunohistochemical study was performed on three meningeal haemangiopericytomas and four cerebellar haemangioblastomas (paraffin embedded) in an attempt to elucidate the uncertain histogenesis of these tumours. The tumour cells of all meningeal haemangiopericytomas show no expression of alpha-smooth muscle actin and, thus, no immunohistochemical proof of their true pericytic nature can be obtained. The stromal cells of cerebellar haemangioblastomas show foci of positive staining for S-100 protein, neuron-specific enolase and synaptophysin, thereby clearly indicating their neuroectodermal origin. These results allow the conclusion that the present nomenclature of these tumours is at least arguable and probably incorrect.

Meningio-angiomatosis

A case is described of a boy five years old who suffered from left-sided muscular weakness since the first months of life and from absences since the second year of life. He died of valproate-induced hepatic insufficiency. Autopsy of the brain revealed meningio-angiomatosis, a rare but rather benign disorder usually characterized by narrow meningothelial proliferations abutting upon cortical plaques and exhibiting proliferations of small vessels with perivascular cuffs of fibroblast-like cells. The peculiarities were that the case lacked any leptomeningeal calcification - in line with the patient's age being the lowest so far reported for pathologically verified meningio-angiomatosis - and also exhibited intracortical clusters of mesenchymal cells that did not form vessels ("free fibroblasts"). Immunohistochemically perivascular cells were negative for S100, GFAP, desmin and factor-8-related antigen and were embedded in interstitial collagen of types III and VI as well as procollagen I, while "free fibroblasts" were surrounded by deposits of basement membrane collagen type IV. The results are consistent with a meningothelial origin of perivascular cells and "free fibroblasts".

Immunocytochemistry of intracranial meningiomas

Fifty meningiomas of four major histological types have been examined by immunocytochemical methods applied to formalin fixed paraffin embedded material and using readily available commercial antisera. The expression of GFAP, S100, NSE, vimentin, cytokeratin, fibronectin and desmoplakin was investigated. The majority of tumours contained NSE (86%) and S100 (78%), and all irrespective of histological type, contained vimentin and fibronectin. The epithelial marker cytokeratin was found in 56% of cases, but showed only focal expression. The relevance of these findings to histogenesis and metabolism is discussed and it is suggested that intermediate filament typing provides valuable information on meningiomas structure and function. The possible role of NSE and S100 in meningeal neoplasm is discussed.

Immunohistochemical characteristics of haemangiopericytic meningiomas: comparison with typical meningiomas, haemangioblastomas and haemangiopericytomas from extracranial sites

The relationship between malignant vascular meningeal tumours and typical meningiomas remains controversial, despite the need for accurate diagnostic distinction between the two, and some forms of vascular meningioma may be more closely allied to haemangioblastomas or extracranial haemangiopericytomas than to true meningiomas. In order to try to clarify the diagnostic characteristics and origins of the entity known as haemangiopericytic meningioma, 10 histologically typical cases were stained by the immunoperoxidase technique with a panel of seven antibodies. The results were compared with those obtained from typical and angiomatous meningiomas, haemangioblastomas and haemangiopericytomas from extracranial sites. Both the haemangiopericytic meningiomas and the extracranial haemangiopericytomas showed a similar staining pattern, which differed from that of the typical and angiomatous meningiomas in the strikingly focal nature of the vimentin staining and the lack of reactivity with antibodies to epithelial elements. The haemangioblastomas were less consistent in their individual staining characteristics, but had a quite different overall pattern from all the other tumour types. It is, therefore, suggested that so-called haemangiopericytic meningiomas are in fact primary haemangiopericytomas of the meninges, antigenically distinct from true meningiomas and displaying a malignant potential appropriate to haemangiopericytomas arising in any other sites.

Prediction of tumor doubling time in recurrent meningiomas. Cell kinetics studies with bromodeoxyuridine labeling

Eight patients with recurrent meningiomas (four malignant, two hemangiopericytic, and two nonmalignant) were given intravenous bromodeoxyuridine (BUdR), 200 mg/sq m, at the time of surgery to label cells in the deoxyribonucleic acid (DNA) synthesis phase; labeled cells were detected in excised tumor specimens by immunoperoxidase staining using anti-BUdR monoclonal antibody. These tumors showed a wide range of BUdR labeling indices (LI's), calculated as the percentage of BUdR-labeled cells divided by the total number of cells scored, from 0.3% to 5.4%. The tumor doubling times (Td's), estimated from serial computerized tomography scans, ranged from 8 to 440 days and showed a close inverse correlation with the BUdR LI's. A semilogarithmic linear regression analysis of these values yielded a correlation coefficient of 0.99. Tumor doubling time (Td) can be estimated using the formula: Td = 500 X Exp (-0.73 X LI), where Exp signifies the natural log base. By predicting the growth rate of meningiomas, the BUdR LI may supplement histopathological diagnosis and improve both the determination of prognosis and the design of treatment modalities in individual patients.

Ultrastructure of cerebellar capillary hemangioblastoma. V. Large pinocytic vacuolar bodies (megalopinocytic vesicles) in endothelial cells

Large pinocytic vacuolar bodies (megalopinocytic vesicles) containing electron-dense granulo-fibrillary material, not previously described in micro-vascular endothelium of brain tumors, were observed in endothelial cells of all five cases of cerebellar hemangioblastoma studied ultrastructurally. They were present in 23% of a total of 132 capillary profiles studied. Some were prominent and aggregated to occupy a large portion of the endothelial cytoplasm. Unlike the ordinary pinocytic vesicles in endothelial cells, they were distributed predominantly in the vicinity of the nucleus and surrounded by abundant organelles. They were irregular and usually several times larger than macropinocytic vesicles. The larger vacuolar bodies were often surrounded by bundles of microfilaments which often anchored on their limiting membrane. They coexisted frequently with Weibel-Palade bodies and occasionally fused with them. Convergence of coated vesicles and micropinocytic vesicles with the vacuolar bodies was present. However, there was no direct contact between the vacuolar bodies and Golgi apparatus, rough and smooth endoplasmic reticulum and mitochondria. The vacuolar bodies were closely associated with pericytic foot processes. It was suggested that they were formed by invagination of the abluminal cytoplasmic membrane with engulfed extracellular material and migrated internally. Discharge of their contents into the vascular lumen and interendothelial space was observed. Some had a disrupted membrane with a suggestion of release of contents into the cytoplasmic matrix. Their function is unknown, but they may serve as a specific vehicle of transport or digestive mechanism in microvascular endothelium under certain pathophysiological conditions, such as neoplasm, to meet the increasing metabolic demands.

Hemangiopericytoma of the meninges of the optic nerve. A clinicopathologic report including electron microscopic observations

A 61-year-old man complained of visual loss of his right eye following a systemic viral illness. At this time, complete ophthalmologic examination failed to disclose any abnormalities. Over the next months the patient developed dramatic loss of vision. Extensive workup, including CT scans, failed to clarify the underlying cause and a diagnosis of optic atropy following optic neuritis was made. The patient remained asymptomatic, but repeated CT scans depicted a fusiform enlargement of the intraorbital portion of the right optic nerve, three years after the onset of visual loss. The presumptive clinical diagnosis was optic nerve meningioma and the tumor was removed via a Krönlein procedure. Histopathologically, a highly vascularized intradural mass that led to compression atrophy of the optic nerve was present. The tumor was composed of fascicles of spindle-shaped cells that were interspersed among numerous, irregular vascular channels. Electron microscopically, the cells disclosed a lucent cytoplasm with a scarcity of organelles, prominent cytoplasmic filaments, numerous micropinocytotic vesicles and subplasmalemmal linear densities (hemidesmosomes). Poorly developed intercellular junctions were present between interdigitating cytoplasmic processes. The tumor cells surrounding the vascular units displayed a continuous basement membrane as well as all the features of well-differentiated pericytes. Away from vascular structures some tumor cells, which showed a focally discontinuous basement membrane, exhibited intermediate features between pericytes and fibroblasts. To the best of our knowledge, this is the first report of a hemangiopericytoma arising from the meninges of the optic nerve.

Clinical pathology of malignant meningiomas

Nineteen cases of malignant meningiomas-seven haemangiopericytic, two papillary and ten of the anaplastic type-were examined clinicopathologically. These were ten male and nine female patients and eleven of these received reoperation for recurrence. Tumours of the hemangiopericytic type had similar angiographic and macrooscopic features and malignant characteristics were found microscopically in some tumours. There were intratumoral cysts in both cases of the papillary type and these tumours had a high cellularity, an increased number of mitosis, haemorrhage and partially haemangiopericytic patterns. Six cases of the anaplastic type had changed from a benign type at recurrence and those tumours had variable features radiographically and macroscopically. Lack of typical arrangement, a large number of mitoses, increased cellularity, focal necrosis, brain infiltration, pleomorphism and anaplasia were found histologically. Four cases of the anaplastic type were diagnosed at the first operation and these tumours had apparently similar angiographic and macroscopic features, but with variable organoid structures and malignant forms, microscopically. Electron microscopic features are also described. In malignant meningiomas, the recurrence rate was high even in cases of total removal. The outcome for these patients was good in the papillary type, relatively good in the haemangiopericytic type and poor in the anaplastic type. From these results therapeutic indications are also suggested.

Invited review. Nervous system antigens

Some of the better characterized proteins (markers) of the nervous system are described. The availability of specific antibodies to these markers has allowed the localization and assay of the proteins in tissue and biological fluids. There is some evidence that autosensitization may occur. Clinical application of these markers includes the evaluation and prognostic significance after stroke and head injury. The diagnostic histopathological use of the markers in the investigation of various tumours is summarized.

Malignant meningioma: clinical and pathological features

The records of 15 patients with a diagnosis of malignant meningioma were reviewed. In one of these patients, in whom invasion of the brain and pituitary gland was the only unusual feature, the tumor was reclassified as benign. Seven tumors, four hemangiopericytomas and two transitional and one syncytial meningioma, were considered to be only borderline-malignant despite necrosis and invasion of the brain, because of few mitoses and regular architecture. Of this group of patients, four men and three women, two are alive and well, three died after incomplete resections, and two succumbed to recurrent tumor that had become inoperable. The other seven patients, six men and one woman, had lesions classified as histologically frankly malignant, on the basis of marked anaplasia and numerous mitoses. These comprised three hemangiopericytomas and three syncytial and one fibrous meningioma. One of these patients is alive and well and the others are dead, three a a result of metastases. The initial clinical course of malignant meningiomas tends to be short but is otherwise indistinguishable from that of benign meningiomas. The chances of recurrence and eventual death are high, and extracranial metastases are not rare. The tumors are most often hemangiopericytomas, but not exclusively so, and men are particularly at risk.

Granulofilamentous inclusions in a meningioma

We have studied the histology, immunocytochemistry, and ultrastructure of a syncytial meningioma which contained the unusual feature of large eosinophilic intracytoplasmic inclusions. Electron microscopic examination revealed that these bodies were granular, osmiophilic masses, closely associated with cytoplasmic filaments of intermediate size. Desmosomal junctions with a somewhat abnormal morphology were also observed, and the possible relationship between the inclusions and the dense components of desmosomes is discussed. This tumor is also compared to other tumors of the central nervous system with hyaline and granulofilamentous inclusions.

Malignant meningioma: ultrastructure and observations on histogenesis

A malignant meningioma was studied by light and electron microscopy. Histologically, the tumour was composed predominantly of spindle shaped cells arranged in interlacing bundles with numerous mitoses and much nuclear atypia. There were many necrotic foci as well as invasion of the cerebral cortex, dura mater and blood vessels. Ultrastructurally, the main findings included moderate plasma membrane interdigitation, many intracytoplasmic filaments, and junctional attachments of three kinds: desmosomes, hemidesmosomes, and zonulae adhaerentes. These subcellular features are suggestive of arachnoidal cell origin.