Case Report Massive Ossification with Hematopoietic Marrow on Both Surfaces of the Expanded Polytetrafluoroethylene Artificial Dura Mater Naoki Maehara1,3, Takato Morioka2, Takafumi Shimogawa3, Satoshi O. Suzuki4, Masahiro Mizoguchi3, Sei Haga1 Key words - Duraplasty - ePTFE - Hematopoietic marrow - Ossification Abbreviations and Acronyms ECoG: Electrocorticography EEG: Electroencephalogram ePTFE: Expanded polytetrafluoroethylene From the Departments of 1Neurosurgery, Kyushu Rosai Hospital, Kitakyushu, and 2Neurosurgery, Fukuoka Children’s Hospital, Fukuoka; 3Neurosurgery, Graduate School of Medical Sciences, Kyusyu University, Fukuoka; and 4 Neuropathology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan To whom correspondence should be addressed: Sei Haga, M.D., Ph.D. [E-mail: sei.haga@gmail.com] Citation: World Neurosurg. (2020) 139:405-409. https://doi.org/10.1016/j.wneu.2020.04.068 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2020 Elsevier Inc. All rights reserved. INTRODUCTION Artificial dural substitutes made from expanded polytetrafluoroethylene (ePTFE) porous material, GORE PRECLUDE Dura Substitute (W. L. Gore & Associates, Inc., Flagstaff, Arizona), have been widely used as artificial dura mater1 because the material does not degenerate or deteriorate and does not adhere to the surrounding tissue.2 In the chronic stage, a thin fibrous membrane has been found to develop, covering the ePTFE sheet.3 We describe a 19-year-old woman in whom massive ossification with hematopoietic marrow was noted on both surfaces of the ePTFE sheet following duraplasty and autologous cranioplasty fixed with titanium miniplates, which took place at the age of 8 years. CASE DESCRIPTION When the patient was 8 years old, she developed an intracerebral hemorrhage - BACKGROUND: Artificial dural substitute made from an expanded polytetrafluoroethylene (ePTFE) sheet has been widely used in surgical application. - CASE DESCRIPTION: We describe a 19-year-old woman in whom massive ossification with hematopoietic marrow was noted on both surfaces of an ePTFE sheet during epilepsy surgery. At age 8, she underwent decompressive craniectomy for a ruptured arteriovenous malformation in the right frontal lobe, followed by duraplasty with an ePTFE sheet and autologous cranioplasty fixed with titanium miniplates. - CONCLUSIONS: Since the ossification was prominent in the wrinkle dents of the ePTFE sheet and fibrotic membrane with repetitive hemorrhagic events was noted under the ePTFE sheet, the most plausible mechanism of ossification development is the organization of epiartificial and subartificial dural hematoma. Surgeons should be aware of the possibility of ossification development when working with ePTFE sheets for duraplasty. in the right frontal lobe due to a ruptured arteriovenous malformation. She underwent emergency evacuation of the hematoma and decompressive craniectomy of the right frontotemporoparietal bone in another hospital. After 3 months, the nidus was totally removed. Duraplasty was performed with an ePTFE sheet. Cranioplasty was performed with a cryopreserved autologous bone flap, which was fixed with titanium miniplates. Postoperatively, her mental development was normal and activities of daily living were independent, although she had left hemiparesis. However, at 12 years of age, she developed epilepsy that manifested as focal aware tonic-clonic seizures in the left limbs. Although she was treated with optimal doses of various antiepileptic drugs including carbamazepine, levetiracetam, phenytoin, valproic acid, lamotrigine, and clobazam, her seizures became intractable. While her seizures were only several seconds in duration, they occurred several times a day. She was referred to us at 18 years of age. A neuroradiologic examination including computed tomographic scans and magnetic resonance images was WORLD NEUROSURGERY 139: 405-409, JULY 2020 performed. The atrophic bone flap of the right frontotemporoparietal craniotomy was fixed with 3 pieces of titanium miniplates (Figure 1A). While the frontal and parietal bones were fixed, the temporal bone was not fixed. There was a large surgical defect in the right frontal lobe and another old lesion in the superior temporal gyrus (see Figure 1B, C-1, D-1, E-1). Under the bone flap, a calcified or ossifying membrane was noted. The membrane overlying the temporal lobe was undulated (see Figure 1B, C-2), and that overlying the frontal lobe followed the convex line (see Figure 1B, D-2, E-2). Under the ossifying membrane, another thick membrane was noted. This was especially thick over the frontal lobe (see Figure 1B). Positron emission tomography with [18F] fluorodeoxyglucose demonstrated the hypometabolism in the right temporal lobe and frontal lobe (see Figure 1F). Interictal electroencephalogram (EEG) showed frequent paroxysmal discharges over the right anterior temporal and frontopolar regions (F8 and Fp2 of the international EEG 10-20 system, respectively) (see Figure 1G-1). Ictal discharges began over the same region www.journals.elsevier.com/world-neurosurgery 405 CASE REPORT NAOKI MAEHARA ET AL. OSSIFICATION ON SURFACE OF EPTFE SHEET Figure 1. (A) Three-dimensional computed tomographic (CT) scan of the skull demonstrates the relationship between the atrophic bone flap of the right frontotemporoparietal craniotomy and titanium miniplates. The frontal bone was fixed with 2 pieces of burr-hole cover-type plates (white arrows), and the parietal bone was fixed with a double-hole plate (red arrow), while the temporal bone was not fixed. (B) Coronal view of the magnetic resonance image with a short-tau inversion recovery sequence and (C-1, D-1, E-1) axial images with fluid-attenuated inversion recovery sequence showing a large surgical defect in the right frontal lobe and another lesion in the right superior temporal gyrus (white arrow in B and C-1). (C-2, D-2, E-2) Bone targeted computed tomography images at a comparable level with that in images (C-1, D-1, E-1), respectively, revealed a calcified or ossifying membrane under the bone flap. The membrane overlying the temporal lobe was waved (red arrows (F8 and Fp2), were attenuated, and then spread to the right frontotemporoparietal region (see Figure 1G-2). At 19 years of age, the patient underwent epilepsy surgery with an 406 www.SCIENCEDIRECT.com in B, yellow arrows in C-2), while that overlying the frontal lobe was positioned along the convex line (blue arrows in B, yellow arrows in D-2 and E-2). The red arrows in E-1 and E-2 indicate an artifact because of an operative hemoclip. Under the membrane, another thick membrane was observed, especially at the frontal lobe (yellow arrows in B). (F) The coronal view of positron emission tomography with 18F-fluorodeoxyglucose, at a comparable level to that of (B), demonstrates hypometabolism in the right temporal lobe and frontal lobe. (G-1) An interictal electroencephalogram (EEG), with an averaged reference, shows frequent paroxysmal discharges in the right anterior temporal and frontopolar regions (F8 and Fp2 of the international EEG 10-20 system, respectively, black lines). (G-2) On ictal EEG, ictal discharges began over the same region (F8 and Fp2), were attenuated, and then spread to the right frontotemporoparietal region. intraoperative electrocorticography (ECoG) recording. Removal of the bone flap revealed marked ossification on the wrinkled ePTFE sheet (Figure 2A). Turning the ePTFE sheet over exposed massive ossification on the back surface of the sheet. This ossification was prominent in the wrinkle dents over the temporal lobe, and there was a thick fibrous membrane covering the cortical WORLD NEUROSURGERY, https://doi.org/10.1016/j.wneu.2020.04.068 CASE REPORT NAOKI MAEHARA ET AL. OSSIFICATION ON SURFACE OF EPTFE SHEET Figure 2. (A) An intraoperative photograph following the removal of the bone flap, the orientation of which matches that shown in Figure 1A. There was marked ossification on the expanded polytetrafluoroethylene (ePTFE) artificial dura matter. (B) Turning the ePTFE sheet over revealed massive ossification on the back surface of the sheet, which was prominent in the wrinkle dents over the temporal lobe, and a thick fibrous membrane covering over the cortical surface. (C) After dissection of the fibrous membrane, the cortical surface was exposed. A surgical scar surface (see Figure 2B). After dissection of the fibrous membrane, the cortical surface was exposed (see Figure 2C). A surgical scar was noted at the frontal lobe, just above the sylvian fissure. was noted at the frontal lobe (yellow arrows), just above the sylvian fissure (blue arrows). A dark red cortical area can be seen at the superior temporal gyrus (white arrows). (D-1) Intraoperative electrocorticographs (ECoG) were recorded with 3 subdural electrodes. (D-2) ECoG revealed frequent paroxysmal discharges (indicated as #) from the dark red temporal cortex (the location of the electrode is indicated as # in C) and continuous irritable beta-activities (indicated as *) from the frontal cortex adjacent to the surgical scar (indicated as * in C). Dark red cortex was also observed at the superior temporal gyrus. Intraoperative ECoG revealed frequent paroxysmal discharges and continuous irritable beta-activities from the dark WORLD NEUROSURGERY 139: 405-409, JULY 2020 red temporal cortex and frontal cortex adjacent to the surgical scar, respectively (see Figure 2D-1, D-2). Cortical resection of these 2 areas was performed. Repeated ECoG recording confirmed www.journals.elsevier.com/world-neurosurgery 407 CASE REPORT NAOKI MAEHARA ET AL. OSSIFICATION ON SURFACE OF EPTFE SHEET Figure 3. (A and B) Histologically, bony tissues with hematopoietic marrow (arrows in B) are noted on both surfaces of the expanded polytetrafluoroethylene (ePTFE) sheet. (C) The membrane underneath the ePTFE sheet consists of a fibrocollagenous tissue, which contains a massive hematoma. (D) Granulation tissue and hemosiderin deposits are noted in the hematoma. Higher magnification views of the areas are indicated by the dashed square in (C). membrane were present to fill the space formed between the skull and the atrophic brain due to the surgical defect. Since preoperative EEG in this case demonstrated that ictal discharges began at the interictal paroxysmal focus, the epilepsy surgery was performed with less invasive intraoperative ECoG recording,7,8 which revealed 2 independent interictal paroxysmal foci: the dark red cortex at the superior temporal gyrus and the frontal cortex adjacent to the surgical scar. Although both lesions were strongly compressed with the ossified ePTFE sheet, they also had a tight topographic relationship with the previous intracerebral old lesions. Furthermore, the histopathologic characteristics of the resected specimen did not contradict the result of the previous hemorrhagic event and surgery. Thus we are not able to make a conclusion regarding the relationship between the massive ossification and epileptogenic lesion. In conclusion, surgeons should be aware of the possibility of ossification development when working with ePTFE sheets for duraplasty. ACKNOWLEDGMENTS the disappearance of the paroxysmal activities. Duraplasty was performed with the fibrous membrane, and the autologous bone flap was fixed in place with titanium miniplates. Postoperatively, with reduced doses of lamotrigine and carbamazepine, the patient's seizures were controlled over 5 years. Histologically, bony tissues with hematopoietic marrow were noted on both surfaces of the ePTFE sheet (Figure 3A and B). The membrane underneath the ossified ePTFE sheet consisted of thick fibrocollagenous tissue, containing a massive hematoma associated with granulation tissue (see Figure 3C). Hemosiderin deposits were noted in the hematoma, indicating repetitive hemorrhagic events (see Figure 3D). The resected frontal lobe tissue showed severe gliosis with Rosenthal fibers, numerous foamy spheroids, and hemosiderin deposits, probably due to the preceding cerebral hemorrhage and surgery. The temporal lobe showed similar pathologic changes, but to a much lesser extent. 408 www.SCIENCEDIRECT.com DISCUSSION The present report describes the first documented case of a patient who developed massive ossification with hematopoietic marrow on both surfaces of an ePTFE sheet. While the exact mechanism of ossification development is only speculative, the most probable explanation is the organization of epiartificial and subartificial dural hematoma. This speculation would explain why the ossification was prominent in the wrinkle dents. The coexistence of the fibrotic membrane under the ossified ePTFE sheet, which had similar histopathologic findings to those of the capsule of chronic subdural hematoma, strongly supports our speculation. Another concern is that the autologous bone flap was fixed with titanium miniplates. Rigid fixation with nonabsorbable titanium in childhood sometimes causes growth restriction of the skull.4-6 However, in the present case, the temporal side of the bone flap was not fixed and the skull actually developed symmetrically. The ossified ePTFE sheet and the We thank Sydney Koke and Jane Charbonneau, DVM, from Edanz Group (www. edanzediting.com/ac) for editing a draft of this manuscript. REFERENCES 1. Miyake S, Fujita A, Aihara H, Kohmura E. New technique for decompresssive duraplasty using expanded polytetrafluoroethylene dura substitute. Neurol Med Chir (Tokyo). 2006;46:104-106. 2. 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Correlation between scalp-recorded electroencephalographic and electrocorticographic activities during ictal period. Seizure. 2007;16:238-247. 8. Morioka T, Hashiguchi K, Nagata S, et al. Additional hippocampectomy in the surgical OSSIFICATION ON SURFACE OF EPTFE SHEET management of intractable temporal lobe epilepsy associated with glioneuronal tumor. Neurol Res. 2007;29:807-815. Citation: World Neurosurg. (2020) 139:405-409. https://doi.org/10.1016/j.wneu.2020.04.068 Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Available online: www.sciencedirect.com Journal homepage: www.journals.elsevier.com/worldneurosurgery 1878-8750/$ - see front matter ª 2020 Elsevier Inc. All rights reserved. Received 11 March 2020; accepted 10 April 2020 WORLD NEUROSURGERY 139: 405-409, JULY 2020 www.journals.elsevier.com/world-neurosurgery 409