Localized surface plasmon resonances of size-selected large silver nanoclusters (n = 70-100) soft-landed on a C60 organic substrate.

Silver nanoclusters (Agn NCs) exhibit a remarkable optical property known as localized surface plasmon resonance (LSPR) in the visible to ultraviolet wavelengths. In this study, we address the size gap in LSPR responses between small NCs and nano-islands by synthesizing large Agn NCs with a countable number of atoms (n = 70-100) using a magnetron sputtering method, which were precisely size-selected and soft-landed onto substrates. The monodispersed Agn NCs were immobilized on a pre-decorated substrate with fullerene (C60) molecules, and their LSPR behaviors were characterized using two-photon photoemission (2PPE) spectroscopy. Due to the distinct polarization selectivity of incident light associated with LSPR, the intensity ratio between p- and s-polarized lights (Ip/Is) in 2PPE spectroscopy serves as a reliable indicator of LSPR and its structural correlations. From n = 70 to 100, the Ip/Is value gradually decreases as the cluster size increases. This decrease is attributed to the enhancement of s-polarized light (Is), indicating that large Agn NCs on a C60 substrate undergo a deformation from spherical to flattened geometries, particularly above approximately n = 55.

Structures, fundamental properties, and potential applications of low-dimensional C60 polymers and other nanocarbons: a review.

Since carbon (C) atom has a variety of chemical bonds via hybridization between s and p atomic orbitals, it is well known that there are robust carbon materials. In particular, discovery of C60 has been an epoch making to cultivate nanocarbon fields. Since then, nanocarbon materials such as nanotube and graphene have been reported. It is interesting to note that C60 is soluble and volatile unlike nanotube and graphene. This indicates that C60 film is easy to be produced on any kinds of substrates, which is advantage for device fabrication. In particular, electron-/photo-induced C60 polymerization finally results in formation of one-dimensional (1D) metallic peanut-shaped and 2D dumbbell-shaped semiconducting C60 polymers, respectively. This enables us to control the physicochemical properties of C60 films using electron-/photo-lithography techniques. In this review, we focused on the structures, fundamental properties, and potential applications of the low-dimensional C60 polymers and other nanocarbons such as C60 peapods, wavy-structured graphene, and penta-nanotubes with topological defects. We hope this review will provide new insights for producing new novel nanocarbon materials and inspire broad readers to cultivate new further research in carbon materials.

We review the structures, fundamental properties, and applications of low-dimensional C₆₀ polymers and other related nanocarbons such as C₆₀ peapods, wavy-structured graphene, and penta-nanotubes from a standpoint of topological defects.

Micro-/macroscopic and density functional studies of the interactions between molybdenum trioxide and C60 molecule.

We have investigated the interactions between C60 and (MoO3)n using scanning tunneling microscopy with spectroscopy (STM/STS) and ex situ ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy in combination with density functional theory (DFT) calculations. The formation of (MoO3)n chemically bound to C60 is energetically favorable due to ΔG < 0 for n = 1, 2, 4, 6, 8, and 9, and they well reproduced the histogram of the height of (MoO3)n on the C60 (111) terrace obtained by a STM height-profile. STS results demonstrated the upward energy shift of both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of C60 in the vicinity of (MoO3)n (n = 6 or 9), which is consistent with the previous results of the co-deposited C60/MoO3 film obtained using photoemission and inverse photoemission spectroscopy [Wang and Gao, Appl. Phys. Lett. 105, 111601 (2014), Yang et al., J. Phys.: Condens. Matter 28, 185502 (2016), and Li et al., J. Phys. Chem. C 118, 4869 (2014)]. Theoretical calculations of (MoO3)n (n = 1, 2, 4, 6, 8, and 9) chemically bound to C60 indicated that 0.01-0.32 holes are injected into C60 by (MoO3)n nanoclusters, and UV-vis-NIR and DFT results found that the hole doping to C60 is caused via the electron transfer from the HOMO of C60 to the LUMO of (MoO3)n. Furthermore, it is noted that the C60-(MoO3)n interactions exhibit a high heat resistance up to 250 °C by examining the UV-vis-NIR spectra of a co-deposited C60/MoO3 (6:4) film before and after thermal annealing. The present findings provide useful information for the practical use of P-type C60-based thermoelectric devices.

Thermally Stable Array of Discrete C60s on a Two-Dimensional Crystalline Adlayer of Macrocycles both in Vacuo and under Ambient Pressure.

A periodic monolayer array of discrete C60s was generated on an atomically flat Au(111) surface with the aid of a template adlayer. The template was a two-dimensional (2D) array of molecular pits prepared on an Au(111) surface through 2D crystallization of shape-persistent macrocycles composed of four carbazole and four salphens/Ni-salphens with a 1 nm hollow. Scanning tunneling microscopy imaging under ultra-high vacuum revealed that the square-shaped macrocycles, with 1.5 nm sides, were arranged with a periodic spacing of approximately 4.0 nm on the Au(111) surface, where the orientation and periodicity of the macrocycles were dependent on their chemical structures. After sublimation of C60s onto the adlayer, a single C60 molecule was entrapped in each pit, and an ordered molecular array of C60s was attained with a pattern similar to that of the macrocycles. The periodic pattern of C60s on the surface was thermally stable up to approximately 200 °C, even under ambient pressure. Scanning tunneling spectroscopy suggested the existence of an electronic interaction between the C60s and the Au(111) surface that was influenced by the macrocycle template on the surface.

Histopathological investigation of the 1p/19q-codeleted gliomas resected following alkylating agent chemotherapy.

PURPOSE: Lower grade gliomas with 1p/19q codeletion are often responsive to chemotherapy, and several of these have been treated using upfront chemotherapy and subsequent resection following tumor volume decrease. This study aimed to elucidate the histological changes and the mechanism of recurrence after alkylating agent chemotherapy in 1p/19-codeleted gliomas. METHODS: Fourteen 1p/19q-codeleted gliomas resected following tumor volume decrease after alkylating agent chemotherapy were included and compared with their pre-chemotherapy specimens. Histological changes were investigated using hematoxylin-eosin staining, and changes in proliferative activity, status of glioma stem cells (GSCs), and tumor-infiltrating macrophages were assessed using immunohistochemistry for Ki-67/MIB-1, CD68 as a pan-macrophage/monocyte marker, CD163 as a presumed marker of M2 polarity, and nestin and CD133 as markers of GSCs. RESULTS: The most frequent histological findings following chemotherapy included a sparse glial background and abundant foamy cell infiltration. The Ki-67/MIB-1 index decreased and the number of CD68 + cells increased after chemotherapy. The increasing rate of CD68 + cells in the post-/pre-chemotherapy specimens was inversely correlated with patient prognosis but not tumor response. The number of CD163 + cells, M2/M1 + M2 ratio, and the ratio of GSCs to total tumor cells increased after chemotherapy, and those in the post-chemotherapy specimens were negatively correlated with patient prognosis. There was a correlation between the M2/M1 + M2 ratio and the ratio of GSCs in both pre- and post-chemotherapy specimens. CONCLUSION: GSCs in conjunction with M2 macrophages constitute the mechanism of resistance to and recurrence after alkylating agent chemotherapy in 1p/19q-codeleted gliomas.

Morphological and optical properties of α- and ß-phase zinc (∥) phthalocyanine thin films for application to organic photovoltaic cells.

We have investigated the morphological and optical properties of α- and ß-phase Zinc Phthalocyanine (ZnPc) thin films for application to organic photovoltaic cells (OPVs). It was found that the α-phase is completely converted to the ß-phase by thermal annealing at 220 °C under ultrahigh vacuum conditions. When the α- to ß-phase transition takes place, the surface roughness of the ZnPc film became flat uniformly with a nanometer order of unevenness by anisotropic growth of crystalline grains along a lateral direction to substrates. Correspondingly, the optical absorbance of the ß-phase film became greater by 1.5-2 times than that of the α-phase one in an ultraviolet-visible-near infrared (UV-vis-NIR) wavelength range, which plays a role in increasing the number of photogenerated excitons. On the contrary, time-resolved photoluminescence measurements showed that the average lifetime of excitons for the ß-phase film became shorter by 1/6-1/7 than that for the α-phase one, which plays a role in decreasing the number of excitons achieving the donor/acceptor interface where excitons are separated to carriers (holes and electrons). Both the increase in the number and the shortening in the average lifetime have a trade-off relationship with each other for contribution to the photoelectric conversion efficiency of OPVs. Then, we examined an external quantum efficiency (EQE) of OPVs using the α- and ß-phase films as a donor and obtained that the former OPV (α-phase) exhibits a higher EQE by ∼2 times than the latter one (ß-phase) in the wavelength range of 400 nm-800 nm.

Synthesis and Characterization of Metal-Encapsulating Si16 Cage Superatoms.

Nanoclusters, aggregates of several to hundreds of atoms, have been one of the central issues of nanomaterials sciences owing to their unique structures and properties, which could be found neither in nanoparticles with several nanometer diameters nor in organometallic complexes. Along with the chemical nature of each element, properties of nanoclusters change dramatically with size parameters, making nanoclusters strong potential candidates for future tailor-made materials; these nanoclusters are expected to have attractive properties such as redox activity, catalysis, and magnetism. Alloying of nanoclusters additionally gives designer functionality by fine control of their electronic structures in addition to size parameters. Among binary nanoclusters, binary cage superatoms (BCSs) composed of transition metal (M) encapsulating silicon cages, M@Si16, have unique cage structures of 16 silicon atoms, which have not been found in elemental silicon nanoclusters, organosilicon compounds, and silicon based clathrates. The unique composition of these BCSs originates from the simultaneous satisfaction of geometric and electronic shell-closings in terms of cage geometry and valence electron filling, where a total of 68 valence electrons occupy the superatomic orbitals of (1S)2(1P)6(1D)10(1F)14(2S)2(1G)18(2P)6(2D)10 for M = group 4 elements in neutral ground state. The most important issue for M@Si16 BCSs is fine-tuning of their characters by replacement of the central metal atoms, M, based on one-by-one adjustment of valence electron counts in the same structure framework of Si16 cage; the replacement of M yields a series of M@Si16 BCSs, based on their superatomic characteristics. So far, despite these unique features probed in the gas-phase molecular beam and predicted by quantum chemical calculations, M@Si16 have not yet been isolated. In this Account, we have focused on recent advances in synthesis and characterizations of M@Si16 BCSs (M = Ti and Ta). A series of M@Si16 BCSs (M = groups 3 to 5) was found in gas-phase molecular beam experiments by photoelectron spectroscopy and mass spectrometry: formation of halogen-, rare-gas-, and alkali-like superatoms was identified through one-by-one tuning of number of total valence electrons. Toward future functional materials in the solid state, we have developed an intensive, size-selected nanocluster source based on high-power impulse magnetron sputtering coupled with a mass spectrometer and a soft-landing apparatus. With scanning probe microscopy and photoelectron spectroscopy, the structure of surface-immobilized BCSs has been elucidated; BCSs can be dispersed in an isolated form using C60 fullerene decoration of the substrate. The intensive nanocluster source also enables the synthesis of BCSs in the 100-mg scale by coupling with a direct liquid-embedded trapping method into organic dispersants, enabling their structure characterization as a highly symmetric "metal-encapsulating tetrahedral silicon-cage" (METS) structure with Frank-Kasper geometry.

Columnar Liquid Crystals from a Giant Macrocycle Mesogen.

Columnar liquid crystals composed of a giant macrocyclic mesogen were prepared. The giant macrocyclic mesogen has a square hollow with a 2.5 nm diagonal, which was bounded by diindolo[3,2-b:2',3'-h]carbazole (diindolocarbazole) moieties as the edges and bis(salicylidene)-o-phenylenediamine (salphen) moieties as the corners. The shape and size of the macrocycle were directly observed by scanning tunneling microscopy (STM). Each side of the bright square in the STM image corresponds to a diindolocarbazole moiety, and the length of the sides was consistent with the result of the single crystal analysis of diindolocarbazole. Finally, we successfully obtained a giant macrocycle with long and branched side chains, which exhibited a rectangular columnar LC phase over a wide temperature range. To the best of our knowledge, it contained the largest discrete inner space of any thermotropic columnar liquid crystal composed of macrocyclic mesogens.

Spectroscopic and theoretical studies on the structural, electronic, and optical properties of zinc octaethylporphyrin/C60 co-deposited films.

We have examined the structural, electronic, and optical properties of zinc-octaethylporphyrin [Zn(OEP)]/C60 co-deposited films to elucidate the donor (D)-acceptor (A) interactions at the D/A interface of heterojunction organic solar cells (OSCs), using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence (PL) spectroscopy in combination with first-principles and semi-empirical calculations. The FT-IR and XRD results indicated that Zn(OEP) and C60 were mixed with each other at the molecular level in the co-deposited film. The theoretical calculations suggested that in the interfacial region, it is energetically preferable for the C60 molecule to face the center of the planar structure of Zn(OEP) at a distance of 2.8 Å rather than the edge of the structure at a distance of 5.0 Å. After consideration of the C60 solvent effects, this coordination model for C60-Zn(OEP) adequately explained the line shift of the UV-vis peaks with respect to the proportion of C60 in the co-deposited films. A comparison of the energy level diagrams of Zn(OEP) before and after the interaction with C60 revealed that the LUMO, HOMO, and HOMO-1 were significantly affected by the interaction with C60. In particular, the HOMO-1 wave function became spread over a portion of C60, although the charge transfer between Zn(OEP) and C60 was almost negligible. Since no PL peaks (S1 → S0) from the excited Soret band of Zn(OEP) were observed for the Zn(OEP)/C60 co-deposited films, the D/A mixing layers played a crucial role in completely dissolving the photogenerated excitons to electrons-hole pairs that cause the short-circuit current, which is relevant to improving the energy conversion efficiency of OSCs.

Chemical characterization of an alkali-like superatom consisting of a Ta-encapsulating Si16 cage.

Chemical characterization was performed for an alkali-like superatom consisting of a Ta-encapsulating Si16 cage, Ta@Si16, deposited on a graphite substrate using X-ray photoelectron spectroscopy (XPS) to element-specifically clarify the local electronic structure of the cage atoms. The XPS spectra derived from Ta 4f and Si 2p core levels have been well modeled with a single chemical component, revealing the formation of a symmetric Si cage around the Ta atom in the deposited nanoclusters. On chemical treatments by heating or oxygen exposure, it is found that the deposited Ta@Si16 is thermally stable up to 700 K and is also exceptionally less reactive toward oxygen compared to other Ta-Si nanoclusters, although some heat degradation and oxidation accompany the treatments. These results show the promising possibility of applying Ta@Si16 as a building block to fabricate cluster-assembled materials consisting of naked nanoclusters.

Phase I/II Study of a Vascular Endothelial Growth Factor Receptor Vaccine in Patients With NF2-Related Schwannomatosis.

PURPOSE: The humanized antivascular endothelial growth factor (VEGF) antibody bevacizumab (Bev) is efficacious for the treatment of NF2-related schwannomatosis (NF2), previously known as neurofibromatosis type 2. This study evaluated the safety and efficacy of a VEGF receptor (VEGFR) vaccine containing VEGFR1 and VEGFR2 peptides in patients with NF2 with progressive schwannomas (jRCTs031180184). MATERIALS AND METHODS: VEGFR1 and VEGFR2 peptides were injected subcutaneously into infra-axillary and inguinal regions, once a week for 4 weeks and then once a month for 4 months. The primary end point was safety. Secondary end points included tolerability, hearing response, imaging response, and immunologic response. RESULTS: Sixteen patients with NF2 with progressive schwannomas completed treatment and were assessed. No severe vaccine-related adverse events occurred. Among the 13 patients with assessable hearing, word recognition score improved in five patients at 6 months and two at 12 months. Progression of average hearing level of pure tone was 0.168 dB/mo during the year of treatment period, whereas long-term progression was 0.364 dB/mo. Among all 16 patients, a partial response was observed in more than one schwannoma in four (including one in which Bev had not been effective), minor response in 5, and stable disease in 4. Both VEGFR1-specific and VEGFR2-specific cytotoxic T lymphocytes (CTLs) were induced in 11 patients. Two years after vaccination, a radiologic response was achieved in nine of 20 assessable schwannomas. CONCLUSION: This study demonstrated the safety and preliminary efficacy of VEGFR peptide vaccination in patients with NF2. Memory-induced CTLs after VEGFR vaccination may persistently suppress tumor progression.

Volumetric measurement of paranasal sinuses and its clinical significance in pituitary neuroendocrine tumors operated using an endoscopic endonasal approach.

Objective: Endoscopic endonasal surgery (EES) for deep intracranial lesions has gained popularity following recent developments in endoscopic technology. The operability of invasive pituitary neuroendocrine tumors (PitNETs) depends on the anatomy of the nasal cavity and paranasal sinus. This study aimed to establish a simple volume reconstruction algorithm of the nasal cavity and paranasal sinus. Additionally, this is the first study to demonstrate the relationship between the segmentation method and the clinical significance in patients with PitNET. Methods: Pre-and postoperative tumor volumes were analyzed in 106 patients with primary (new-onset) PitNETs (80 nonfunctioning and 26 functioning) who underwent EES. The efficiency and accuracy of the semiautomatic segmentation with manual adjustments (SSMA) method was compared with other established segmentation methods for volumetric analysis in the nasal cavity and paranasal sinuses. Correlations between the measured nasal cavity and paranasal sinus volumes and the extent of tumor removal were evaluated. Results: The SSMA method yielded accurate and time-saving results following the volumetric analyses of nasal cavity and paranasal sinuses with complex structures. Alternatively, the manual and semiautomatic segmentation methods proved time-consuming and inaccurate, respectively. The sphenoid sinus volume measured by SSMA was significantly correlated with the extent of tumor removal in patients with nonfunctioning Knosp grade 3 and 4 PitNET (r = 0.318; p = 0.015). Conclusion: The volume of sphenoid sinus potentially could predict the extent of resection due to better visualization of the tumor for PitNETs with CS invasion.

A simple combined approach using anterior transpetrosal and retrosigmoid approach: A case report.

Background: A combined transpetrosal approach (CTP) is often used for large lesions in the posterior cranial fossa (PCF). Although CTP provides a wide surgical corridor, it has complex and time-consuming bony work of mastoidectomy and cosmetic issues. Here, we describe a simple combined surgical technique to approach the supratentorial region, anterolateral surface of the brainstem, petroclival region, and foramen magnum by drilling only the petrous apex with a combination of retrosigmoid approach (RA). Clinical presentation: A 27-year-old female was referred with extra-axial left cerebellopontine angle space-occupying epidermoid cyst extending to the prepontine cistern, anterior to the basilar artery, superior to the chiasma, and caudally to the foramen magnum. A one-stage surgical procedure using the anterior transpetrosal approach (ATP) and RA was performed after one-piece temporal-suboccipital craniotomy. These two approaches complemented each other well. Near-total removal was achieved. Conclusion: A one-stage surgical procedure using ATP and RA provides the wider viewing and better visualization of the PCF with minimal technical difficulty.

Octithiophene on Cu(III) and Au(III): formation and electronic structure of molecular chains and films.

Adsorption and electronic structure of octithiophene (8T) molecules on Cu(III) and Au(III) surfaces are investigated using scanning tunneling microscopy (STM) and spectroscopy (STS) at room temperature. We find a large difference in adsorption behavior of 8T molecules on the two surfaces. At the initial stage of adsorption, 8T molecules are stabilized in the form of molecular chain on a terrace of Cu(III), whereas neither such chain structure nor isolated 8T molecules have been observed on a terrace of Au(III). By increasing the amount of adsorbed molecules, a disordered monolayer film is formed on Cu(III) while a well-ordered monolayer film is formed on Au(III). From the spectroscopic investigations using bias-dependent STM images and STS spectra and by comparing the data with theoretical calculations, it is found that the electronic property of 8T molecules in the molecular chain on Cu(III) is different from that of a free-standing 8T molecule while that in the monolayer film on Au(III) keeps original character of the free-standing 8T molecule. The present study shows that adsorption of 8T molecules on Cu(III) results in a formation of adsorption-induced states near the Fermi level.

Unraveling the reasons behind lead phthalocyanine acting as a good absorber for near-infrared sensitive devices.

Lead phthalocyanine (PbPc) is well known to be used as a good near-infrared (NIR) light absorber for organic solar cells (OSCs) and photodetectors. The monoclinic and triclinic phases have been understood to absorb the visible and NIR regions, respectively, so far. In the present study, we demonstrated from the absorption spectra and theoretical analysis that the visible band considerably originates from not only the monoclinic but also the amorphous and triclinic phases, and revealed the exciton dynamics in the PbPc film from static/time-resolved photoluminescence (PL), which are first reported. By comparing the external quantum efficiency between PbPc- and ZnPc-based OSCs in relation to their structure, morphology, and optical (absorption and PL) characteristics, we unraveled the reasons behind the PbPc film used as a good absorber for NIR-sensitive devices.

Nanoscale control of reversible chemical reaction between fullerene C60 molecules using scanning tunneling microscope.

The nanoscale control of reversible chemical reactions, the polymerization and depolymerization between C60 molecules, has been investigated. Using a scanning tunneling microscope (STM), the polymerization and depolymerization can be controlled at designated positions in ultrathin films of C60 molecules. One of the two chemical reactions can be selectively induced by controlling the sample bias voltage (V(s)); the application of negative and positive values of V(s) results in polymerization and depolymerization, respectively. The selectivity between the two chemical reactions becomes extremely high when the thickness of the C60 film increases to more than three molecular layers. We conclude that STM-induced negative and positive electrostatic ionization are responsible for the control of the polymerization and depolymerization, respectively.

Resolving Site-Specific Energy Levels of Small-Molecule Donor-Acceptor Heterostructures Close to Metal Contacts.

The active material of optoelectronic devices must accommodate for contacts which serve to collect or inject the charge carriers. It is the purpose of this work to find out to which extent properties of organic optoelectronic layers change close to metal contacts compared to known properties of bulk materials. Bottom-up fabrication capabilities of model interfaces under ultrahigh vacuum and single-atom low temperature (LT)-STM spectroscopy with density functional theory (DFT) calculations are used to detect the spatial modifications of electronic states such as frontier-orbitals at interfaces. The system under consideration is made of a silver substrate covered with a blend of C60 and ZnPc molecules of a few monolayers. When C60 and ZnPc are separately adsorbed on Ag(111), they show distinct spectroscopic features in STM. However, when C60 is added to the ZnPc monolayer, it shows scanning tunneling spectra similar to ZnPc, revealing a strong interaction of C60 with the ZnPc induced by the substrate. DFT calculations on a model complex confirm the strong hybridization of C60 with ZnPc layer upon adsorption on Ag(111), thus highlighting the role of boundary layers where the donor-acceptor character is strongly perturbed. The calculation also reveals a significant charge transfer from the Ag to the complex that is likely responsible for a downward shift of the molecular LUMO in agreement with the experiment.

Confined Hot Electron Relaxation at the Molecular Heterointerface of the Size-Selected Plasmonic Noble Metal Nanocluster and Layered C60.

The plasmonic response of metallic nanostructures plays a key role in amplifying photocatalytic and photoelectric conversion. Since the plasmonic behavior of noble metal nanoparticles is known to generate energetic charge carriers such as hot electrons, it is expected that the hot electrons can enhance conversion efficiency if they are transferred into a neighboring molecule or semiconductor. However, the method of transferring the energized charge carriers from the plasmonically generated hot electrons to the neighboring species remains controversial. Herein, we fabricated a molecularly well-defined heterointerface between the size-selected plasmonic noble-metal nanoclusters (NCs) of Agn (n = 3-55)/Aun (n = 21) and the organic C60 film to investigate hot electron generation and relaxation dynamics using time-resolved two-photon photoemission (2PPE) spectroscopy. By tuning the NC size and the polarization of the femtosecond excitation photons, the plasmonic behavior is characterized by 2PPE intensity enhancement by 10-100 times magnitude, which emerge at n ≥ 9 for Agn NCs. The 2PPE spectra exhibit contributions from low-energy electrons forming coherent plasmonic currents and hot electrons with an excitation energy up to photon energy owing to two-photon excitation of an occupied state of the Agn NC below the Fermi level. The time-resolved pump-probe measurements demonstrate that plasmon dephasing generates hot electrons which undergo electron-electron scattering. However, no photoemission occurs via the charge transfer state forming Agn+C60- located in the vicinity of the Fermi level. Thus, this study reveals the mechanism of ultrafast confined hot electron relaxation within plasmonic Agn NCs at the molecular heterointerface.

Neuroendoscopic Technique for Recurrent Chronic Subdural Hematoma with Small Craniotomy.

AIM: To present a case series describing an endoscopic technique with a small craniotomy for recurrent chronic subdural hematoma (rCSDH) treatment. MATERIAL AND METHODS: A total of 17 patients with rCSDH underwent neuroendoscopic hematoma removal with a small craniotomy under local or general anesthesia. The skin incision of the initial surgery on the convexity of the skull was extended, and a burr hole was created for a small craniotomy. After the removal of the outer membrane and hematoma through a small craniotomy, the hematoma was evacuated with a suction tube using the rigid endoscope. The entire hematoma cavity circumference was irrigated, while septations and trabeculae in the hematoma were cut. After hematoma evacuation, the inner membrane was incised and removed to allow brain expansion. Postoperative follow-up was performed for at least 6 months. RESULTS: The regrowth rate of rCSDH after the neuroendoscopy was 5.9%. One patient with recurrent chronic subdural hematoma regrowth required neuroendoscopy again, but no re-recurrence was observed for the next 6 months. All cases were successfully managed using this technique and the postoperative seizure rate was 23.5%. CONCLUSION: This neuroendoscopic technique with a small craniotomy could be useful for recurrent chronic subdural hematoma because the hematoma and septations can be visualized and evacuated along the entire circumference of the hematoma cavity, and the inner membrane can be torn to allow brain expansion.