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The current move towards digital pathology enables pathologists to use artificial intelligence (AI)‐based computer programmes for the advanced analysis of whole slide images. However, currently, the best‐performing AI algorithms for image analysis are deemed black boxes since it remains – even to their developers – often unclear why the algorithm delivered a particular result. Especially in medicine, a better understanding of algorithmic decisions is essential to avoid mistakes and adverse effects on patients. This review article aims to provide medical experts with insights on the issue of explainability in digital pathology. A short introduction to the relevant underlying core concepts of machine learning shall nurture the reader's understanding of why explainability is a specific issue in this field. Addressing this issue of explainability, the rapidly evolving research field of explainable AI (XAI) has developed many techniques and methods to make black‐box machine‐learning systems more transparent. These XAI methods are a first step towards making black‐box AI systems understandable by humans. However, we argue that an explanation interface must complement these explainable models to make their results useful to human stakeholders and achieve a high level of causability, i.e. a high level of causal understanding by the user. This is especially relevant in the medical field since explainability and causability play a crucial role also for compliance with regulatory requirements. We conclude by promoting the need for novel user interfaces for AI applications in pathology, which enable contextual understanding and allow the medical expert to ask interactive ‘what‐if’‐questions. In pathology, such user interfaces will not only be important to achieve a high level of causability. They will also be crucial for keeping the human‐in‐the‐loop and bringing medical experts' experience and conceptual knowledge to AI processes.

The interest in implementing digital pathology (DP) workflows to obtain whole slide image (WSI) files for diagnostic purposes has increased in the last few years. The increasing performance of technical components and the Food and Drug Administration (FDA) approval of systems for primary diagnosis led to increased interest in applying DP workflows. However, despite this revolutionary transition, real world data suggest that a fully digital approach to the histological workflow has been implemented in only a minority of pathology laboratories. The objective of this study is to facilitate the implementation of DP workflows in pathology laboratories, helping those involved in this process of transformation to identify: (a) the scope and the boundaries of the DP transformation; (b) how to introduce automation to reduce errors; (c) how to introduce appropriate quality control to guarantee the safety of the process and (d) the hardware and software needed to implement DP systems inside the pathology laboratory. The European Society of Digital and Integrative Pathology (ESDIP) provided consensus-based recommendations developed through discussion among members of the Scientific Committee. The recommendations are thus based on the expertise of the panel members and on the agreement obtained after virtual meetings. Prior to publication, the recommendations were reviewed by members of the ESDIP Board. The recommendations comprehensively cover every step of the implementation of the digital workflow in the anatomic pathology department, emphasizing the importance of interoperability, automation and tracking of the entire process before the introduction of a scanning facility. Compared to the available national and international guidelines, the present document represents a practical, handy reference for the correct implementation of the digital workflow in Europe.

Intracranial arterial aneurysms can pose life-threatening risks to patients, so understanding the cause and the progression of these lesions is important for choosing the right treatment. This Review argues that aneurysms are a symptom of an underlying vascular disease rather than constituting a disease on their own. The authors classify intracranial aneurysms by vessel wall pathology and demonstrate that knowledge of the morphology and pathology of this structure is important in determining the therapeutic approach. An aneurysm is a focal dilatation of an arterial blood vessel. Luminal forces, such as high blood flow, shear stress and turbulence, are implicated in the pathogenesis of intracranial aneurysms, and luminal characteristics, such as sac size and morphology, are usually essential to the clinical decision-making process. Despite frequent clinical emphasis on the vessel lumen, however, the pathology underlying the formation, growth and rupture of an aneurysm mainly resides in the vessel wall. Research on the morphology and histopathology of the vessel wall reveals that intracranial aneurysms do not constitute a single disease, but are a shared manifestation of a wide range of diseases, each of which has a unique natural history and optimum therapy. This Review classifies intracranial aneurysms by vessel wall pathology, and demonstrates that understanding the morphology and pathology of this structure is important in determining the therapeutic approach. The article concludes that aneurysms represent a symptom of an underlying vascular disease rather than constituting a disease on their own. Key Points Intracranial aneurysms do not constitute a single disease, but are a manifestation of a wide range of diseases Aneurysmal diseases vary in their natural histories and optimum treatment strategies Despite frequent clinical emphasis on the vessel lumen, the pathology underlying aneurysm formation, growth and rupture mainly resides in the vessel wall A classification of intracranial aneurysms based on vessel wall pathology is important to understand these life-threatening conditions and to determine the best therapeutic approaches

Accepting the hypothesis that cancers are self-organizing, opportunistic systems, it is crucial to understand the collective behavior of cancer cells in their tumorous heterogeneous environment. In the present paper, we ask the following basic question: Is this self-organization of tumor evolution reflected in the manner in which malignant cells are spatially distributed in their heterogeneous environment? We employ a variety of nontrivial statistical microstructural descriptors that arise in the theory of heterogeneous media to characterize the spatial distributions of the nuclei of both benign brain white matter cells and brain glioma cells as obtained from histological images. These descriptors, which include the pair correlation function, structure factor and various nearest neighbor functions, quantify how pairs of cell nuclei are correlated in space in various ways. We map the centroids of the cell nuclei into point distributions to show that while commonly used local spatial statistics (e.g., cell areas and number of neighboring cells) cannot clearly distinguish spatial correlations in distributions of normal and abnormal cell nuclei, their salient structural features are captured very well by the aforementioned microstructural descriptors. We show that the tumorous cells pack more densely than normal cells and exhibit stronger effective repulsions between any pair of cells. Moreover, we demonstrate that brain gliomas are organized in a collective way rather than randomly on intermediate and large length scales. The existence of nontrivial spatial correlations between the abnormal cells strongly supports the view that cancer is not an unorganized collection of malignant cells but rather a complex emergent integrated system.

Objective We aimed to delineate the distribution of periventricular nodular heterotopia (PNH) in patients with 22q11.2 microdeletion syndrome (22q11.2DS) and place this in the context of other genetic forms of PNH. Methods We retrospectively analyzed brain imaging and postmortem data available for adult patients with 22q11.2DS. We included only those with good quality MRI data (n = 29) in addition to two patients with PNH identified through postmortem studies. We also reviewed the pattern of PNH in all genetic conditions reported with this phenotype. Results Of the total seven patients (M = 4, F = 3; age: 19–61 years) identified to have PNH, six had a history of seizures, six had schizophrenia, six had variable levels of intellectual disability, and two had obsessive compulsive disorder. In all seven patients, the nodules were located over the dorsal pole of the frontal horn of the lateral ventricles. The nodules were small, noncontiguous, and ranged in number from 1 to 10 per individual. Our review identified 37 genetic conditions associated with PNH. With the cases reported here, 22q11.2DS becomes the fifth most commonly reported genetic condition, and the third most common copy number variation, associated with PNH. Interpretation The neuropsychiatric manifestations in our patients with PNH support other data indicating abnormal neurodevelopment as part of the pathogenesis of 22q11.2DS.The location and cellular characteristics of PNH in 22q11.2DS overlaps with a group of migrating postnatal interneurons termed Arc cells, although more research is needed to confirm that PNH in 22q11.2DS represents Arc cells arrested in their migratory pathway.

Objective Neurofibromatosis type 1 (NF1) patients have a 13% risk of developing a malignant peripheral nerve sheath tumor (MPNST). Many MPNSTs are histopathologically complex, with regions exhibiting features of the original benign plexiform neurofibroma (PNF), of an atypical PNF, or of MPNST showing varying degrees of de-differentiation. This study analyzed the genetic alterations associated with this pathological heterogeneity in order to identify the genetic processes involved in transformation from a benign to an aggressive malignant tumor. Methods A histological and molecular analysis of a single MPNST tumor that was subdivided into three histopathologically distinct regions, a benign PNF (region 1), an atypical PNF (region 2), and a high-grade MPNST (region 3), was carried out. Tumor DNA from each region was analyzed in conjunction with the patient's lymphocyte DNA. Somatic mutation analyses included loss-of heterozygosity (LOH), MLPA analysis, NF1 gene sequencing, and a microarray comparative genomic hybridisation (array CGH) analysis. Results The patient had a germline NF1 splice-site mutation. The NF1-associated LOH analysis found that LOH increased in the three tumor areas, with 9, 42, and 97% LOH evident in regions 1, 2, and 3, respectively. Additional genetic changes, including losses of TP53, RB1, CDKN2A, and of several oncogenes and cell-cycle genes, were found only in the malignant MPNST (region 3). Array CGH also identified genomic gains and losses in DNA from region 3. Discussion This is the first study that correlates the histological and molecular changes associated with MPNST development, confirming the significant cellular and genetic heterogeneity that poses both diagnostic and therapeutic challenges.

Pathology education is a core component of medical training, and its literature is critical for refining educational modalities. We performed a cross-sectional bibliometric analysis to explore publications on pathology education, focusing on new medical education technologies. The analysis identified 64 pathology journals and 53 keywords. Relevant articles were collected using a web application, PaperScraper, developed to accelerate literature search. Citation data were collected from multiple sources. Descriptive statistics, with time period analysis, were performed using Microsoft Excel and visualised with Flourish Studio. Two article groups were further investigated with a bibliometric software, VOSViewer, to establish co-authorship and keyword relationships. 8946 citations were retrieved from 905 selected articles. Most articles were published in the last decade (447, 49.4%). The top journals were (184), (122) and the (117). The highest number of citations was found for (2120), followed by (2098) and (1142). Authors with different backgrounds had the greatest number of articles and citations. 12 co-authorship, 3 keyword and 8 co-citation clusters were found for the social media/online resources group, 8 co-authorship, 4 keyword and 7 co-citation clusters for the digital pathology/virtual microscopy/mobile technologies group. The analysis revealed a significant increase in publications over time. The emergence of digital teaching and learning resources played a major role in this growth. Overall, these findings underscore the transformative potential of technology in pathology education.

Focal myositis secondary to an intramuscular vascular malformation has rarely been reported in the literature. We describe a 21-year-old woman presenting with left thigh pain. Imaging of the thigh muscles showed a vascular malformation and muscle biopsy demonstrated focal changes diagnosed initially as myositis. Ischaemia is thought to be the responsible mechanism.

Evidence suggests hyperglycemia is associated with worse outcomes in glioblastoma (GB). This study aims to confirm the association between glycemia during radiotherapy (RT) and temozolomide (TMZ) treatment and overall survival (OS) in patients with newly diagnosed GB. This retrospective study included GB patients treated with RT and TMZ from 2004 to 2011, randomly divided into independent derivation and validation datasets. Time-weighted mean (TWM) glucose and dexamethasone dose were collected from start of RT to 4 weeks after RT. Univariate (UVA) and multivariable (MVA) analyses investigated the association of TWM glucose and other prognostic factors with overall survival (OS). In total, 393 patients with median follow-up of 14 months were analyzed. In the derivation set (n = 196) the median OS was 15 months and median TWM glucose was 6.3 mmol/L. For patients with a TWM glucose ≤6.3 and >6.3 mmol/L, median OS was 16 and 13 months, respectively (p = 0.03). On UVA, TWM glucose, TWM dexamethasone, age, extent of surgery, and performance status were associated with OS. On MVA, TWM glucose remained an independent predictor of OS (p = 0.03) along with TWM dexamethasone, age, and surgery. The validation set (n = 197), with similar baseline characteristics, confirmed that TWM glucose ≤6.3 mmol/L was independently associated with longer OS (p = 0.005). This study demonstrates and validates that glycemia is an independent predictor for survival in GB patients treated with RT and TMZ.

Schwannomas of the abducens nerve are extremely uncommon tumors. Here, we report the case of a 26-year-old woman who presented with a 6th nerve palsy and was found to have a large tumor at the right side of her pons. Neuropathologic exam revealed a cellular schwannoma with a high proliferation index. The case is presented in its clinical, neurosurgical and neuropathologic aspects and the literature on 6th nerve schwannomas is reviewed.