Akimoto Nimura

Pelvic floor dysfunction is a common condition in adult women. In addition to the levator ani, the obturator internus, a lateral pelvic wall muscle, has been suggested to be anatomically and mechanically associated with pelvic floor morphology. Here, we quantitatively characterized age‐related morphological changes in the obturator internus and levator ani using geometric morphometric analysis. We hypothesized a significant association between principal components accounting for major shape variation and age. This cross‐sectional study included 27 adult women aged 25–83 years with gynecological conditions but without pelvic floor disorders based on clinical assessment and imaging findings. Standardized pelvic magnetic resonance imaging scans were obtained between April 2024 and July 2024 at a single tertiary care center. Elliptic Fourier analysis was applied to the segmented obturator internus contours; a landmark‐based method was used to evaluate the combined shape of the obturator internus and levator ani. Principal component analysis and linear regression were performed to assess associations with age. Procrustes analysis of variance was used to evaluate the overall shape–age relationships. Elliptic Fourier analysis revealed that increasing age was significantly associated with relative narrowing of the superior portion, an inferior morphological shift of the medial surface groove, and increased prominence of the medial eminence of the obturator internus. A landmark‐based analysis revealed similar age‐related shape changes, including inferiorly directed shape changes of the groove, verticalization of the levator ani, and widening of the levator hiatus. Procrustes analysis revealed a significant relationship between age and overall shape variation. Aging was associated with coordinated age‐related morphological remodeling of the obturator internus and levator ani.

Automatic segmentation is increasingly used in medical imaging, but many tools require command-line operation and environment setup. TotalSegmentator provides open-source multiorgan segmentation for computed tomography (CT) and magnetic resonance imaging (MRI) data, yet its routine use may be challenging for nontechnical users. Herein, we describe the design, implementation, and functionality of Instant3D, a lightweight, open-source graphical user interface (GUI) frontend for TotalSegmentator. Instant3D was developed in Python using PyQt6. It accepts DICOM folders, NIfTI files, and NRRD files as input and allows users to select regions of interest (ROIs) through a suggestion-enabled interface. The GUI executes TotalSegmentator as the backend. Default outputs include STL meshes for 3D visualization and NIfTI segmentation images, with optional SVG masks and CSV files containing volumetric measurements. SVG masks are interoperable with SegRef3D for slice-level review and refinement of automated segmentation results. Batch processing is supported. Functionality was tested using representative CT and MRI datasets. Instant3D successfully imported supported formats, executed TotalSegmentator through the GUI, and generated expected outputs, including STL, NIfTI, SVG, and CSV files. Representative datasets demonstrated successful workflow completion and compatibility with SegRef3D. Batch processing generated organized output files for multiple input datasets, confirming workflow feasibility. Instant3D simplifies TotalSegmentator execution and facilitates generation of reusable 3D reconstruction outputs. While not a replacement for comprehensive visualization platforms, it complements them by providing a streamlined workflow for ROI selection, batch processing, and multiformat export. Instant3D may serve as a practical tool for research, education, quantitative imaging, and 3D model generation.

Purpose The tissue deep to the posterior wall of the inguinal canal, between the transversalis fascia and peritoneum, remains insufficiently understood. We aimed to develop a compartment-like three-dimensional morphological model of this tissue by clarifying its structure-associated organization, continuity, and spatial relationships around the deep inguinal ring. Methods Five inguinal regions from three formalin-fixed adult male cadavers were examined: one by anterior dissection, three by peritoneal dissection, and one by serial block-face imaging using the CoMBI system. Three-dimensional reconstruction was performed from the serial block-face images. Results The tissue between the transversalis fascia and peritoneum was not arranged as a uniform layer of preperitoneal fat. Three structure-associated fibroadipose units related to the inferior epigastric vessels, ductus deferens, and testicular vessels were delineated, together with the vesicoumbilical fibroadipose territory (VFT) and median-paramedian adipose region (MPAR). The ductus deferens- and testicular vessel-associated units extended directly toward the deep inguinal ring, whereas the inferior epigastric vessel-associated unit, VFT, and MPAR occupied adjacent territories. Conclusion The findings support a compartment-like three-dimensional morphological model in which the fibroadipose units and territories remain open and continuous, rather than a set of histologically closed, independent anatomical compartments. Distinguishing ring-directed fibroadipose units from adjacent territories may help clarify how established fascia-, space-, and ring-based concepts relate to the internal fibroadipose arrangement.

Background: Restricted elbow flexion sometimes persists even after stretching the triceps brachii. Although prior descriptions have noted that a small muscle bundle is located between the posterior elbow joint capsule and the triceps brachii, its anatomical relationship with surrounding muscles and dynamic changes during forearm rotation remain unclear. We hypothesized that the small muscle bundle separates from the triceps and contributes to forearm rotation. This study aimed to clarify the anatomical structure of the small muscle bundle and its dynamic changes during forearm rotation. Methods: We analyzed 19 elbow specimens from 16 Japanese cadavers, donated to the Department of Anatomy, Institute of Science Tokyo, to identify the small muscle bundle covering the joint capsule. One specimen was excluded because of severe osteophytes, leaving 18 specimens randomly allocated to three groups (10, 3, and 5 specimens in the macroscopic examination, intramuscular nerve distribution examination, and histological examination groups, respectively). Additionally, we investigated 10 elbows of five healthy volunteers to evaluate dynamic changes in the small muscle bundle and joint capsule using ultrasonography during forearm rotation. Results: Anatomically, deep to the triceps brachii, a small muscle bundle covering the posterior elbow joint capsule was identified. The small muscle bundle was continuous laterally with the anconeus muscle and was separated from the triceps by loose connective tissue. The small muscle bundle and the anconeus were innervated by the same branches of the radial nerve. Ultrasonically, the small muscle bundle was found to be significantly thicker during forearm supination (6.0 ± 1.4 mm) than pronation (4.1 ± 1.0 mm; p = 0.002), and the distance between the olecranon fossa and the posterior edge of the joint capsule was significantly shorter during supination (8.9 ± 1.1 mm) than pronation (9.6 ± 1.1 mm; p = 0.023). Conclusions: The small muscle bundle formed a muscular complex with the anconeus and was distinct from the triceps. The small muscle bundle deep to the triceps may act during forearm rotation, affecting the posterior elbow joint capsule. These anatomical and ultrasonographic findings may contribute to a better understanding of the pathophysiology of restricted elbow flexion.

BackgroundAnatomical variations in the branching patterns of the aortic arch affect endovascular access, surgical planning, and cerebral perfusion strategies. However, the quantitative relationship between branching topology and the frequency distribution of these variations remains unclear. We aimed to explore whether topological differences among final aortic arch branching configurations are associated with their reported frequencies.MethodsThis retrospective, cross-sectional, observational study analyzed seven representative aortic arch branching types as independent anatomical phenotypes using data derived from a large meta-analysis. Each configuration was quantified using two newly defined topological indices: the Node-Shift Score, representing differences in the relative positions of branching nodes, and the Edge-Loss-Change Score, describing alterations in arterial connectivity relative to the reference configuration. Regression analyses using linear, logarithmic, and exponential models were performed to evaluate the relationship between the topological scores and frequencies.ResultsHigher topological scores were associated with lower configuration frequencies. In the exponential model, each one-unit increase in the Node-Shift Score and Edge-Loss-Change Score was associated with approximately 0.11-fold and 0.013-fold decreases in configuration frequency, respectively.ConclusionsThe frequency distribution was described by an exponential model based on the two topological scores. This study proposes an exploratory quantitative framework for characterizing the frequency distribution of common and rare aortic arch branching configurations from a topological perspective.

Hip arthroscopy requires a capsulotomy to achieve adequate visualization and access; however, an excessive incision can increase the risk of postoperative instability. This technical note describes a less‐invasive capsulotomy technique guided by the “gluteus minimus sign,” a fibrous membrane connecting the main tendon of the gluteus minimus to the joint capsule. Cadaveric analysis confirmed that this fibrous membrane corresponds to the anterosuperior region of the femoral neck. Most gluteus minimus functions can be preserved by limiting the anterior extension of the capsulotomy to within this sign. When additional anterior exposure is necessary, superficial tendon fibers can be incised using an arthroscopic knife. This technique offers a safe, anatomically informed, and strategically targeted capsulotomy that balances preservation of joint stability with adequate surgical access.

Accurate and efficient image segmentation is crucial in anatomy, histology, and pathology research. Conventional manual approaches are time‐consuming, whereas fully automated artificial intelligence segmentation requires substantial manual correction owing to inaccuracy. To address this, we developed SegRef3D, a tool integrating the Segment Anything Model 2 with multiframe tracking and interactive refinement functions, enabling streamlined segmentation workflows for anatomical research. SegRef3D is implemented as a standalone, offline desktop application that operates entirely in a local environment, eliminating the need for cloud‐based services. SegRef3D provides a unified workflow from data import to segmentation, object tracking, refinement, and three‐dimensional model export. Users can specify segmentation prompts through bounding box input, track objects across multiple frames with start–end range selection, and refine results using intuitive Add to Mask and Erase from Mask tools. Up to 20 objects can be handled simultaneously, with each assigned a unique color. The software supports the Standard Tessellation Language output for three‐dimensional modeling and includes volume measurement functions. The SegRef3D prototype, called Seg&Ref, has been applied in studies using serial histological sections, correlative microscopy with block‐face imaging, and pelvic magnetic resonance imaging. Building on these applications, SegRef3D further enhances usability and enables a seamless workflow. SegRef3D offers an accessible, efficient, and accurate segmentation environment tailored for morphological and anatomical studies. Combining artificial intelligence‐powered automatic segmentation with human‐guided refinement in a user‐friendly graphical user interface bridges the gap between research needs and computational methods. By supporting applications that span traditional anatomy and modern pathology, SegRef3D provides a versatile platform for integrative morphological analysis. Its open‐source availability ensures its broad applicability in research, education, and clinical training in the anatomical sciences.

The specific anatomical features of the obturator internus, particularly those of its medial surface, remain insufficiently characterized. This study investigated the morphology of the obturator internus muscle by focusing on the shape of its medial surface and potential age‐related changes. Through dissection of anatomical specimens and in vivo pelvic magnetic resonance imaging (MRI) analysis, we identified a consistent groove‐like structure on the medial surface of the muscle and divided it into distinct regions: a superior portion with radiating muscle fibers and an inferior portion with parallel‐aligned fibers. This division was characterized by differing fascicle orientations, with interspersed adipose tissue occasionally observed at the boundary. MRI scans of 27 women aged 25–83 years demonstrated that this groove was consistently visible; its location and depth were quantified. The groove position showed a weak negative trend with age, but this relationship was not statistically significant and may have been underpowered. No significant correlation was found for groove depth. By delineating the consistent bipartite architecture of the obturator internus and identifying its age‐related variation, this study provides a detailed anatomical characterization of the medial surface of the obturator internus that may serve as a reference for future anatomical and clinical investigations involving the hip–pelvic interface.