Ischaemic Strokes Caused by Spontaneous Cerebral Air Embolism, A Rare Complication of Interstitial Lung Disease.

Air embolism is a rare cause of ischaemic stroke. It is known that air can enter the cerebral arterial circulation from pulmonary venous circulation through a bronchovenous fistula, or in cases of pulmonary barotrauma in deep-sea diving. We describe a case of spontaneous cerebral air embolism against a background of advanced interstitial lung disease (ILD). To our knowledge, this case demonstrates a mechanism of stroke in ILD patients that has not been previously described. LEARNING POINTS: This case demonstrates a mechanism of stroke in patients with severe interstitial lung disease (ILD) that has not been previously described, and we suggest that in cases of advanced ILD, clinicians should consider this as a possible mechanism of stroke. The management of these patients should include transferring them to hyperbaric facilities to prevent further air emboli.

A lymphocyte chemoaffinity axis for lung, non-intestinal mucosae and CNS.

Tissue-selective chemoattractants direct lymphocytes to epithelial surfaces to establish local immune environments, regulate immune responses to food antigens and commensal organisms, and protect from pathogens. Homeostatic chemoattractants for small intestines, colon, and skin are known1 2, but chemotropic mechanisms selective for respiratory tract and other non-intestinal mucosal tissues (NIMT) remain poorly understood. Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17, a chemoattractant cytokine whose expression by epithelial cells of airways, upper gastrointestinal and squamous mucosae unifies the NIMT and distinguishes them from intestinal mucosae. Single-cell transcriptomic analyses show that GPR25 is induced on innate lymphocytes prior to emigration to the periphery, and is imprinted in secondary lymphoid tissues on activated B and T cells responding to immune challenge. GPR25 characterizes B and T tissue resident memory and regulatory T lymphocytes in NIMT and lungs in humans and mediates lymphocyte homing to barrier epithelia of the airways, oral cavity, stomach, biliary and genitourinary tracts in mouse models. GPR25 is also expressed by T cells in cerebrospinal fluid and CXCL17 by neurons, suggesting a role in CNS immune regulation. We reveal widespread imprinting of GPR25 on regulatory T cells, suggesting a mechanistic link to population genetic evidence that GPR25 is protective in autoimmunity3,4. Our results define a GPR25-CXCL17 chemoaffinity axis with the potential to integrate immunity and tolerance at non-intestinal mucosae and the CNS.

Crystalline Hepatopathy Associated With Bietti Crystalline Dystrophy: A Striking Manifestation of Disordered Fatty Acid Metabolism.

Bietti crystalline dystrophy (BCD) is a rare heritable retinal disease characterized by crystal deposition primarily in the retina. It is associated with atrophy of the retinal pigment epithelium (RPE) and is caused by variants in CYP4V2 , which encodes a cytochrome P450 hemethiolate protein superfamily member. CYP4V2 is involved in the selective hydrolysis of saturated medium chain fatty acids, and patients with BCD demonstrate abnormalities in fatty acid metabolism, including abnormal lipid profiles and the accumulation of the pathogenic crystals within the RPE, which leads to the visual pathologies characteristic of BCD. However, the precise identity of the crystals is currently unknown, and BCD has no established extraocular manifestations. Here, we report granulomatous hepatitis associated with abundant diffuse crystalline clefts in the hepatic parenchyma in 3 patients with retinal dystrophy and dyslipidemia: 2 with pathogenic CYP4V2 variants and 1 patient with clinical ophthalmologic findings suggestive of BCD but without available genetic testing. The unique and striking histologic features unifying the liver biopsies in all 3 patients strongly support a process related to abnormal fatty acid metabolism underlying the genetic disease of BCD, expanding the spectrum of BCD and shedding light on the importance of CYP4V2 in systemic fatty acid metabolism.

Perivascular Epithelioid Cell-Family Tumors in Children, Adolescents and Young Adults:Clinicopathologic Features in 70 Cases.

CONTEXT.­: Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal tumors of uncertain histogenesis expressing smooth muscle and melanocytic markers. The clinicopathologic spectrum in young patients is not well documented. OBJECTIVE.­: To describe a multi-institutional series of PEComas in children, adolescents, and young adults. DESIGN.­: PEComas, not otherwise specified (NOS); angiomyolipomas (AMLs); lymphangioleiomyomatosis; and clear cell sugar tumors were retrospectively identified from 6 institutions and authors' files. RESULTS.­: Seventy PEComas in 64 patients (median age, 15 years) were identified. They were more common in females (45 of 64 patients), occurring predominately in kidney (53 of 70), followed by liver (6 of 70). Thirty-four patients had confirmed tuberous sclerosis complex (TSC), 3 suspected TSC mosaicism, 2 Li-Fraumeni syndrome (LFS) and 1 neurofibromatosis type 1. Most common variants were classic (49 of 70) and epithelioid (8 of 70) AML. Among patients with AMLs, most (34 of 47) had TSC, and more TSC patients had multiple AMLs (15 of 36) than non-TSC patients (2 of 13). Two TSC patients developed malignant transformation of classic AMLs: 1 angiosarcomatous and 1 malignant epithelioid. Lymphangioleiomyomatosis (5 of 70) occurred in females only, usually in the TSC context (4 of 5). PEComas-NOS (6 of 70) occurred exclusively in non-TSC patients, 2 of whom had LFS (2 of 6). Three were malignant, 1 had uncertain malignant potential, and 2 were benign. All 4 PEComas-NOS in non-LFS patients had TFE3 rearrangements. CONCLUSIONS.­: Compared to the general population, TSC was more prevalent in our cohort; PEComas-NOS showed more frequent TFE3 rearrangements and possible association with LFS. This series expands the spectrum of PEComas in young patients and demonstrates molecular features and germline contexts that set them apart from older patients.

Soft Tissue Perivascular Epithelioid Cell Tumors.

Perivascular epithelioid cell tumors (PEComas) are a heterogenous group of mesenchymal neoplasms with a mixed myomelanocytic immunophenotype. PEComa-family tumors include angiomyolipoma, lymphangioleiomyomatosis, and a large category of rare neoplasms throughout the body that are now classified under the umbrella term "PEComa." This review focuses on recent advances in the clinicopathological and molecular features of PEComas, with an emphasis on PEComas that originate in soft tissue.

Melanoma in infants, caused by a gene fusion involving the anaplastic lymphoma kinase (ALK).

We describe the first cases of pediatric melanoma with ALK fusion gene arising within giant congenital melanocytic nevi. Two newborn boys presented with large pigmented nodular plaques and numerous smaller satellite nevi. Additional expansile nodules developed within both nevi and invasive melanomas were diagnosed before 10 months of age in both boys. Oncogenic driver mutations in NRAS and BRAF were absent in both cases. Instead, oncogenic ZEB2::ALK fusion genes were identified in both the nevus and melanoma developing within the nevus. In both cases, tumors were noted by ultrasound in utero, demonstrated significant nodularity at birth, and progressed to melanoma in the first year of life suggesting that congenital nevi with ALK fusion genes may behave more aggressively than those with other mutations. As ALK kinase inhibitors are effective against a range of tumors with similar ALK fusion kinases, identifying ALK fusion genes in congenital melanocytic nevi may provide an opportunity for targeted therapy.

The Pathologic Diagnosis of Pediatric Soft Tissue Tumors in the Era of Molecular Medicine: The Sarcoma Pediatric Pathology Research Interest Group Perspective.

CONTEXT.­: Pediatric soft tissue tumors are one of the areas of pediatric pathology that frequently generate consult requests. Evolving classification systems, ancillary testing methods, new treatment options, research enrollment opportunities, and tissue archival processes create additional complexity in handling these unique specimens. Pathologists are at the heart of this critical decision-making, balancing responsibilities to consider expediency, accessibility, and cost-effectiveness of ancillary testing during pathologic examination and reporting. OBJECTIVE.­: To provide a practical approach to handling pediatric soft tissue tumor specimens, including volume considerations, immunohistochemical staining panel recommendations, genetic and molecular testing approaches, and other processes that impact the quality and efficiency of tumor tissue triage. DATA SOURCES.­: The World Health Organization Classification of Soft Tissue and Bone Tumors, 5th edition, other recent literature investigating tissue handling, and the collective clinical experience of the group are used in this manuscript. CONCLUSIONS.­: Pediatric soft tissue tumors can be difficult to diagnose, and evaluation can be improved by adopting a thoughtful, algorithmic approach to maximize available tissue and minimize time to diagnosis.

Clinical Features of SARS-CoV-2 Infection During Pregnancy and Associated Placental Pathologies.

SUMMARY: We reviewed the clinicopathologic findings of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-exposed placentas at our institution. We identified patients diagnosed with SARS-CoV-2 during pregnancy (March-October 2020). Clinical data included gestational age at diagnosis and delivery and maternal symptoms. Hematoxylin and eosin slides were reviewed for maternal vascular malperfusion, fetal vascular malperfusion, chronic villitis, amniotic fluid infection, intervillous thrombi, fibrin deposition, and infarction. Immunohistochemistry (IHC) for coronavirus spike protein and RNA in situ hybridization (ISH) for SARS-CoV-2 was performed on a subset of blocks. A review of placentas from age-matched patients received March-October 2019 was conducted as a comparison cohort. A total of 151 patients were identified. Placentas in the 2 groups were similar in weight for gestational age and had similar rates of maternal vascular malperfusion, fetal vascular malperfusion, amniotic fluid infection, intervillous thrombi, fibrin deposition, and infarction. Chronic villitis was the only significantly different pathologic finding between cases and controls (29% of cases showed chronic villitis vs. 8% of controls, P <0.001). Overall, 146/151 (96.7%) cases were negative for IHC and 129/133 (97%) cases were negative for RNA ISH. There were 4 cases that stained positively for IHC/ISH, 2 of which showed massive perivillous fibrin deposition, inflammation, and decidual arteriopathy. Coronavirus disease 2019 (COVID-19)-positive patients were more likely to self-identify as Hispanic and more likely to have public health insurance. Our data suggests SARS-CoV-2 exposed placentas that stain positively for SARS-CoV-2 show abnormal fibrin deposition, inflammatory changes, and decidual arteriopathy. The group of patients with clinical COVID-19 are more likely to show chronic villitis. IHC and ISH evidence of viral infection is rare.

The Tabula Sapiens: A multiple-organ, single-cell transcriptomic atlas of humans.

Molecular characterization of cell types using single-cell transcriptome sequencing is revolutionizing cell biology and enabling new insights into the physiology of human organs. We created a human reference atlas comprising nearly 500,000 cells from 24 different tissues and organs, many from the same donor. This atlas enabled molecular characterization of more than 400 cell types, their distribution across tissues, and tissue-specific variation in gene expression. Using multiple tissues from a single donor enabled identification of the clonal distribution of T cells between tissues, identification of the tissue-specific mutation rate in B cells, and analysis of the cell cycle state and proliferative potential of shared cell types across tissues. Cell type-specific RNA splicing was discovered and analyzed across tissues within an individual.

Leiomyomatosis in an Infant With a SUFU Splice Site Variant: Case Report.

Heterozygous loss-of-function variants in the suppressor of fused protein gene (SUFU) can result in Gorlin syndrome, which is characterized by an increased frequency of basal cell carcinoma, medulloblastoma, odontogenic keratocysts, as well as other tumors. We describe a case of a 5-month-old female who presented with multiple intra-abdominal leiomyomata and was found to have a likely pathogenic splice site variant in the SUFU gene. This is the first reported case of leiomyomatosis secondary to a pathogenic SUFU variant in an infant and may represent an early, atypical presentation of Gorlin syndrome.

The Risk of Colonic Strictures with Colitis Following Hemolytic Uremic Syndrome: A Case Report of a Toddler.

Gastrointestinal manifestations of hemolytic uremic syndrome (HUS) are rare in pediatrics, but can have significant impact on the course of the disease. While various infectious etiologies are associated with HUS, Enterohemorrhagic Escherichia coli (EHEC) has been a focus of interest in its role in post-diarrheal HUS. We report a previously healthy 3-year-old boy who presented with bloody diarrhea, was found to be EHEC positive, and developed gastrointestinal complications of HUS including chronic colitis and strictures. The case illustrates that, though rare, HUS can have long-term gastrointestinal effects.

ALK rearrangements in infantile fibrosarcoma-like spindle cell tumours of soft tissue and kidney.

AIMS: Recurrent alterations in receptor tyrosine kinase (RTK) and downstream effectors are described in infantile fibrosarcoma (IFS)/cellular congenital mesoblastic nephroma (cCMN) and a subset of spindle cell sarcomas, provisionally designated 'NTRK-rearranged' spindle cell neoplasms. These two groups of tumours demonstrate overlapping morphologies and harbour alterations in NTRK1/2/3, RET, MET, ABL1, ROS1, RAF1 and BRAF, although their relationship is not fully elucidated. We describe herein a cohort of paediatric tumours with clinicopathological features not typical for inflammatory myofibroblastic tumour, but rather with similarities to cCMN/IFS harbouring ALK fusions. METHODS AND RESULTS: Clinicopathological features were assessed and partner agnostic targeted RNA sequencing on clinically validated platforms were performed. Tumours occurred in patients aged from 2 to 10 years (median age 2 years) with a 2:2 male to female ratio and an average size of 8.4 cm. Two tumours arose in soft tissues and two in the kidney. Morphological features included spindle to ovoid cells arranged in long fascicles or haphazardly within a myxoid to collagenised stroma; a subset of cases had either dilated, ectatic vessels or focal perivascular hyalinosis. By immunohistochemistry, all cases tested showed cytoplasmic expression of anaplastic lymphoma kinase (ALK) and one case demonstrated co-expression of CD34 and S100. CONCLUSIONS: This series of ALK-rearranged IFS-like tumours expands the spectrum of targetable kinases altered in these tumours and reinforces the potential overlap between IFS/cCMN-like tumours and the provisional entity of 'NTRK-rearranged' spindle cell neoplasms.

Severe delayed hypersensitivity reactions to IL-1 and IL-6 inhibitors link to common HLA-DRB1*15 alleles.

OBJECTIVES: Drug reaction with eosinophilia and systemic symptoms (DRESS) is a severe, delayed hypersensitivity reaction (DHR). We observed DRESS to inhibitors of interleukin 1 (IL-1) or IL-6 in a small group of patients with Still's disease with atypical lung disease. We sought to characterise features of patients with Still's disease with DRESS compared with drug-tolerant Still's controls. We analysed human leucocyte antigen (HLA) alleles for association to inhibitor-related DHR, including in a small Kawasaki disease (KD) cohort. METHODS: In a case/control study, we collected a multicentre series of patients with Still's disease with features of inhibitor-related DRESS (n=66) and drug-tolerant Still's controls (n=65). We retrospectively analysed clinical data from all Still's subjects and typed 94/131 for HLA. European Still's-DRESS cases were ancestry matched to International Childhood Arthritis Genetics Consortium paediatric Still's cases (n=550) and compared for HLA allele frequencies. HLA association also was analysed using Still's-DRESS cases (n=64) compared with drug-tolerant Still's controls (n=30). KD subjects (n=19) were similarly studied. RESULTS: Still's-DRESS features included eosinophilia (89%), AST-ALT elevation (75%) and non-evanescent rash (95%; 88% involving face). Macrophage activation syndrome during treatment was frequent in Still's-DRESS (64%) versus drug-tolerant Still's (3%; p=1.2×10-14). We found striking enrichment for HLA-DRB1*15 haplotypes in Still's-DRESS cases versus INCHARGE Still's controls (p=7.5×10-13) and versus self-identified, ancestry-matched Still's controls (p=6.3×10-10). In the KD cohort, DRB1*15:01 was present only in those with suspected anakinra reactions. CONCLUSIONS: DRESS-type reactions occur among patients treated with IL-1/IL-6 inhibitors and strongly associate with common HLA-DRB1*15 haplotypes. Consideration of preprescription HLA typing and vigilance for serious reactions to these drugs are warranted.

RNA splicing programs define tissue compartments and cell types at single-cell resolution.

The extent splicing is regulated at single-cell resolution has remained controversial due to both available data and methods to interpret it. We apply the SpliZ, a new statistical approach, to detect cell-type-specific splicing in >110K cells from 12 human tissues. Using 10X Chromium data for discovery, 9.1% of genes with computable SpliZ scores are cell-type-specifically spliced, including ubiquitously expressed genes MYL6 and RPS24. These results are validated with RNA FISH, single-cell PCR, and Smart-seq2. SpliZ analysis reveals 170 genes with regulated splicing during human spermatogenesis, including examples conserved in mouse and mouse lemur. The SpliZ allows model-based identification of subpopulations indistinguishable based on gene expression, illustrated by subpopulation-specific splicing of classical monocytes involving an ultraconserved exon in SAT1. Together, this analysis of differential splicing across multiple organs establishes that splicing is regulated cell-type-specifically.

Arteriovenous Malformations-Current Understanding of the Pathogenesis with Implications for Treatment.

Arteriovenous malformations are a vascular anomaly typically present at birth, characterized by an abnormal connection between an artery and a vein (bypassing the capillaries). These high flow lesions can vary in size and location. Therapeutic approaches are limited, and AVMs can cause significant morbidity and mortality. Here, we describe our current understanding of the pathogenesis of arteriovenous malformations based on preclinical and clinical findings. We discuss past and present accomplishments and challenges in the field and identify research gaps that need to be filled for the successful development of therapeutic strategies in the future.

Sclerosing Epithelioid Fibrosarcoma of the Kidney: First Reported Case in a Young Child.

Sclerosing epithelioid fibrosarcoma (SEF) is a rare variant of fibrosarcoma primarily arising in the deep soft tissue of the extremities and trunk. Despite having the morphologic appearance of a low-grade sarcoma, it generally has an aggressive clinical course with frequent local recurrences and distant metastases. It typically occurs in middle aged adults and is characterized by immunoexpression of MUC4 and recurrent gene fusions, most commonly EWSR1-CREB3L1. We report a primary renal SEF in a 4-year-old male. To our knowledge, this is the youngest patient reported with SEF and the second case of SEF in a pre-adolescent child. It is the eleventh reported case of primary renal SEF in the literature. While SEF arising in visceral organs is rare, the kidney is the most common primary site of any visceral organ. This case demonstrates SEF can occur in pre-adolescents, is an important consideration when evaluating sarcomas in young children, and should be considered in the differential diagnosis for primary renal tumors.

Capillary cell-type specialization in the alveolus.

In the mammalian lung, an apparently homogenous mesh of capillary vessels surrounds each alveolus, forming the vast respiratory surface across which oxygen transfers to the blood1. Here we use single-cell analysis to elucidate the cell types, development, renewal and evolution of the alveolar capillary endothelium. We show that alveolar capillaries are mosaics; similar to the epithelium that lines the alveolus, the alveolar endothelium is made up of two intermingled cell types, with complex 'Swiss-cheese'-like morphologies and distinct functions. The first cell type, which we term the 'aerocyte', is specialized for gas exchange and the trafficking of leukocytes, and is unique to the lung. The other cell type, termed gCap ('general' capillary), is specialized to regulate vasomotor tone, and functions as a stem/progenitor cell in capillary homeostasis and repair. The two cell types develop from bipotent progenitors, mature gradually and are affected differently in disease and during ageing. This cell-type specialization is conserved between mouse and human lungs but is not found in alligator or turtle lungs, suggesting it arose during the evolution of the mammalian lung. The discovery of cell type specialization in alveolar capillaries transforms our understanding of the structure, function, regulation and maintenance of the air-blood barrier and gas exchange in health, disease and evolution.

Dissecting the Cardiac Conduction System: Is It Worthwhile?

BACKGROUND: Pathologic examination of conduction system (CS) is not routinely performed, and histologic changes are mostly reported in forensic practice. METHODS: We studied the value of dissecting the CS in a cohort of pediatric patients with unexplained sudden death or severe, inexplicable arrhythmias. Histopathologic changes present in CS components were recorded and correlated with findings noted in other cardiac structures. RESULTS: Twenty-one subjects (11 unexplained sudden deaths and 10 life-threatening arrhythmias) were identified; 18 (86%) had CS pathologic abnormalities. In 13 patients (62%), the CS findings mirrored those found in other cardiac sections (inflammation, allograft vasculopathy, vascular fibromuscular dysplasia, cardiomyopathy-related changes, and tumor/tumor-like conditions). Five cases (24%) had abnormalities restricted to CS (bundle of His [BH] with fibrotic scar and patch material following ventricular septal defect repair, inflammation, BH with fibrosis and calcifications, and intimal fibroplasia of sinoatrial node artery). CONCLUSIONS: Pathologic changes within the CS are present in a high number of pediatric patients presenting with unexplained sudden death or life-threatening arrhythmias. Frequently, the findings mirror those observed in other cardiac structures. However, in a significant number of cases (24%), the changes are restricted to CS and likely explain the patients' symptoms or cause of death, suggesting that systematic dissection of CS unveils valuable information.