Primary intraosseous papillary intralymphatic angioendothelioma of the distal femoral epiphysis: a case report with literature review.

INTRODUCTION: Papillary intralymphatic angioendothelioma (PILA) is an exceptionally rare metastasizing soft tissue tumor. It tends to arise in the subcutaneous tissues of distal extremities in children. Only four intraosseous PILA cases have been reported until now in English language literature. CASE REPORT: We present a case of PILA arising in the distal femoral epiphysis of a 50-year-old female patient. It started as a relentless pain in her left knee. A plain radiography revealed a radiolucent area in the left internal femoral condyle. Computerized tomography revealed a 1-cm lytic lesion with a sclerotic rim. Magnetic resonance images showed a significant bone marrow edema signal focused on a 1-cm subchondral lesion suggestive of an intraarticular osteoid osteoma. Histologically, the tumor contained vascular channels covered by a single endothelial layer with intraluminal papillary endothelial structures lined with hobnail cells. Immunohistochemically, the cells were positive for ERG, CD31, and D2-40. The tumor underwent cryoablation and 6 months later, after local recurrence or tumor persistence, a wide tumor resection was referred. After 7 years of follow-up, the patient displayed neither local recurrence nor distant metastases. CONCLUSION: Primary intraosseous PILAs are exceedingly rare tumors that should be considered in the differential diagnosis of vascular bone tumors.

Utility of cervical pessary in the prevention of preterm birth in triplet pregnancies: A single-center observational retrospective study of 165 triplet pregnancies.

OBJECTIVE: Premature births are a health problem arising in triplet pregnancies, resulting in high levels of morbidity and mortality. The objective of this study is to evaluate the utility of cervical pessaries in reducing prematurity (<34 weeks) in triplet pregnancies. METHODS: This is a single-center, retrospective case-control study regarding triplet pregnancies with follow-up at the La Paz University Hospital between 2000 and 2023. Maternal characteristics, obstetric and perinatal outcomes, and the use of cervical pessaries were examined. RESULTS: 165 triplet pregnancies were analyzed: 87 (52.7 %) in the case group (premature triplet pregnancies) and 78 in the control group (non-premature triplet pregnancies). A cervical pessary was inserted in 15 (17.2 %) triplet pregnancies in the case group and in 12 (16.7 %) triplet pregnancies in the control group (p = 0.92; OR = 1.04 (0.46-2.35)). A pessary was later inserted in the non-premature group (p = 0.01). The risk of preterm labor and the use of tocolytics ± glucocorticoids were found to be significantly more frequent in the premature group, with p = 0.01; OR = 2.30 (1.21-4.36) and p < 0.01; OR = 2.36 (1.23-4.44), respectively. Protocol-based cesarean sections were more frequent in the non-premature group (p < 0.01), while cesarean sections due to maternal complications (p < 0.01) and premature membrane rupture (p < 0.01) were more frequent in the premature group. CONCLUSION: The cervical pessary is not useful in preventing preterm births (< 34 weeks) in triplet pregnancies. It is likely that being pregnant with triplets is a powerful independent factor associated with prematurity, despite other pregnancy conditions. Women who are pregnant with triplets and at risk of preterm labor and those taking tocolytics ± glucocorticoids may benefit from pessary insertion.

Why do patients with urinary diversions have an increased risk of bone fracture? A systematic review on risk factors for osteoporosis and bone mineral density loss in this group of patients.

INTRODUCTION: Patients undergoing radical cystectomy with urinary diversions (UD) are at increased risk of bone fractures compared to the general population. Although a loss of bone mineral density (BMD) has been described in patients with UD, we still do not know with certainty why these patients follow this tendency. OBJECTIVE: We performed a systematic review of the available literature to analyze the prevalence of osteoporosis and bone alterations in patients with ileal UD and the possible associated risk factors. EVIDENCE ACQUISITION: We systematically searched PubMed® and Cochrane Library for original articles published before December 2022 according to PRISMA guidelines. EVIDENCE SYNTHESIS: A total of 394 publications were identified. We selected 12 studies that met the inclusion criteria with 496 patients included. Six of the twelve studies showed decreased BMD values. Prevalence of osteoporosis was specified in three articles, with values ranging ​​from 0% to 36%. Risk factors such as age, sex, body mass index, metabolic acidosis and renal function appear to have an impact on bone tissue reduction, while type of UD, follow-up, 25-hydroxyvitamin D and parathormone had less evidence or contradictory data. The heterogeneity of the studies analyzed could led to interpretation bias. CONCLUSIONS: UD are associated with multiple risk factors for osteoporosis and bone fractures. Identifying patients at highest risk and establishing diagnostic protocols in routine clinical practice are essential to reduce the risk of fractures and the resulting complications.

Comparison of maternal, fetal, obstetric and neonatal outcomes for 234 triplet pregnancies conceived in vivo versus IVF and ICSI conceptions.

RESEARCH QUESTION: Is there a difference in maternal, fetal, obstetric and neonatal outcomes for triplet pregnancies when comparing in vivo conceptions with those conceived by assisted reproductive technology (ART)? DESIGN: This single-centre, retrospective cohort study included all triplet pregnancies followed up at La Paz University Hospital, Madrid between 2000 and 2022. The characteristics of the pregnant women, and maternal, fetal, obstetric and perinatal outcomes were examined. Univariate and multivariate statistical analyses were performed. RESULTS: In total, 234 triplet pregnancies were analysed: 92 in the natural and assisted insemination conception group (in-vivo conception) and 142 in the in vitro fertilization and intracytoplasmic sperm injection conception group (ART conception). ART triplet pregnancies were more common between 2000 and 2010 (P = 0.003). The percentage of monochorionic triamniotic pregnancies was significantly higher (P = 0.02) in the in-vivo conception group, and the percentage of dichorionic triamniotic pregnancies was significantly higher (P = 0.003) in the ART conception group. After adjusting for confounders, intrauterine growth restriction (IUGR) remained significantly more common in the ART conception group (adjusted odds ratio 8.65, 95% CI 1.66-45.03; P = 0.01). Differences in maternal age (P = 0.61), threatened preterm labour (P = 0.10), Apgar score ≤5 at 5 min (P = 0.99), umbilical cord pH <7.20 (P = 0.99) and fetal death (P = 0.99) disappeared after adjustment for confounders. CONCLUSION: ART triplet pregnancies had a higher rate of IUGR than in vivo triplet pregnancies. This could be related to higher maternal age, and higher rates of Apgar score ≤5 at 5 min and umbilical cord pH <7.20 in these pregnancies. In these cases, placental examination could provide valuable information.

Prevalencia de acidosis metabólica en derivaciones ileales tras más de un año de la cistectomía radical y repercusiones metabólicas secundarias asociadas / Prevalence of metabolic acidosis in ileal diversions more than one year after radical cystectomy and associated secondary metabolic effects

Introducción y objetivo La acidosis metabólica (AM) es una alteración conocida en pacientes con derivaciones ileales. Es más frecuente en etapas tempranas postoperatorias y disminuye con el tiempo. Nuestro objetivo es determinar su prevalencia tras más de un año de seguimiento, analizar sus factores de riesgo y evaluar su impacto en diferentes perfiles metabólicos. Materiales y métodos Realizamos un estudio observacional entre enero de 2018 y septiembre de 2022 siguiendo las normas STROBE. La AM fue definida con valores de bicarbonato venoso <22mEq/l. Analizamos 133 pacientes con una media de seguimiento de 55,24±42,36 meses. Resultados Se identificaron 16 (12%) pacientes con AM. Los pacientes con y sin AM fueron comparables en edad, sexo y tiempo de seguimiento. El grupo con AM presentó una mayor tasa de anemia (68,75 vs. 19,65%; p<0,001) e insuficiencia renal (100 vs. 45,29%; p<0,001) y niveles venosos estadísticamente significativos mayores de creatinina, cloro, potasio, hormona paratiroidea y fósforo, pero menores valores de hemoglobina, filtrado glomerular, colesterol total, vitamina D, calcio y albúmina (todos p<0,05). El filtrado glomerular fue el único factor de riesgo independiente relacionado con la AM (OR: 0,914; IC 95%: 0,878-0,95; p<0,0001), demostrando una estrecha correlación con los valores de bicarbonato venoso (r=0,387; p<0,001). Conclusiones La AM es una alteración poco prevalente en derivaciones urinarias ileales transcurrido más de un año de la cistectomía, pero tiene implicaciones en el metabolismo hematológico, renal, proteico, lipídico y óseo. Aconsejamos su monitorización en pacientes con insuficiencia renal para poder realizar un diagnóstico y tratamientos precoces (AU)

Introduction and objective Metabolic acidosis (MA) is a well-known complication in patients with ileal urinary diversions. It is common in the early postoperative stages and decreases over time. Our objective is to investigate the prevalence of MA after more than one year of follow-up, identify the associated risk factors, and analyze its secondary metabolic consequences. Materials and methods We conducted an observational study between January 2018 and September 2022 following the STROBE guidelines. MA was defined as a serum bicarbonate level <22mEq/L. Finally, we analyzed 133 patients with a mean follow-up of 55.24±42.36 months. Results MA was observed in 16 (12%) patients. Patients with and without MA were comparable in age, sex, and follow-up time. The group with MA presented a higher rate of anemia (68,75% vs 19.65%, P<.001) and renal failure (100% vs 45.29%, P<.001), statistically significant higher levels of serum creatinine, chloride, potassium, parathyroid hormone, and phosphorus but lower serum values of hemoglobin, renal glomerular filtration rate, total cholesterol, vitamin D, calcium, and albumin (all P<.05). Renal glomerular filtration rate was the only independent risk factor related to the development of MA (OR: 0.914; 95% CI: 0.878-0.95; P<.0001), proving a close correlation with venous bicarbonate values (r=.387, P<.001). Conclusions MA is a little prevalent disorder in ileal urinary diversions more than one year after radical cystectomy is performed but it has secondary consequences on hematologic, renal, protein, lipid, and bone metabolism. We recommend to a close follow-up in patients with renal failure for early diagnosis and treatment (AU)

Primary aneurysmal bone cyst of hands and feet: A series of 14 cases.

Aneurysmal bone cyst (ABC) is a relatively rare, benign bone tumor that occurs exceptionally in the hands and feet. The objective of this article is to present clinical, radiological, histopathological features and management of a series of 14 primary ABC cases in these unusual locations. Eight cases occurred in hands and six in feet. We present the first reported subungual case to occur in the hand. The average age of the patients was 26 years (range 7 to 49), with half being over the age of twenty at diagnosis. The male to female ration was 9:5. In radiological terms, ABC appeared as an expansive lesion with internal septa and without cortical disruption. Twelve cases displayed the classic multicystic morphology and two cases were of the solid variant. "Blue bone" was detected in 50 % of the specimens. Treatment consisted of curettage, excision, or amputation in all cases. Recurrence rate was observed in 35 % of the cases, with the similar ABC morphology as the original samples. New therapeutic options have been proposed on their own or in combination with surgery to reduce local recurrence rates.

Prevalence of metabolic acidosis in ileal diversions more than one year after radical cystectomy and associated secondary metabolic effects.

INTRODUCTION AND OBJECTIVE: Metabolic acidosis (MA) is a well-known complication in patients with ileal urinary diversions. It is common in the early postoperative stages and decreases over time. Our objective is to investigate the prevalence of MA after more than one year of follow-up, identify the associated risk factors, and analyze its secondary metabolic consequences. MATERIALS AND METHODS: We conducted an observational study between January 2018 and September 2022 following the STROBE guidelines. MA was defined as a serum bicarbonate level ​​<22mEq/L. Finally, we analyzed 133 patients with a mean follow-up of 55.24 ± 42.36 months. RESULTS: MA was observed in 16 (12%) patients. Patients with and without MA were comparable in age, sex, and follow-up time. The group with MA presented a higher rate of anemia (68,75% vs 19,65%, p < 0.001) and renal failure (100% vs 45,29%, p < 0.001), statistically significant higher levels of serum creatinine, chloride, potassium, parathyroid hormone, and phosphorus but lower serum values ​​of hemoglobin, renal glomerular filtration rate, total cholesterol, vitamin D, calcium, and albumin (all p < 0.05). Renal glomerular filtration rate was the only independent risk factor related to the development of MA (OR 0.914; 95% CI 0.878-0.95; p < 0.0001), proving a close correlation with venous bicarbonate values ​​(r = 0.387, p < 0.001). CONCLUSIONS: MA is a little prevalent disorder in ileal urinary diversions more than one year after radical cystectomy is performed but it has secondary consequences on hematologic, renal, protein, lipid, and bone metabolism. We recommend to a close follow-up in patients with renal failure for early diagnosis and treatment.

First Reported Case of Malignant Ectomesenchymoma with p.Leu122Arg Mutation in MYOD1 Gene: Extensive Intra- and Extracranial Tumor in a 15-Year-Old Female.

BACKGROUND: Ectomesenchymomas (EMs) are extremely rare neoplasms composed of malignant mesenchymal components and neuroectodermal derivatives. They are described in a wide variety of locations, with the head and neck region being one of the most frequently involved areas. EMs are usually managed as high-risk rhabdomyosarcomas and have similar outcomes. METHODS: We present the case of a 15-year-old female with an EM that arose in the parapharyngeal space and extended into the intracranial space. RESULTS: Histologically, the tumor presented an embryonal rhabdomyosarcomatous mesenchymal component and the neuroectodermal component was constituted by isolated ganglion cells. Next-generation sequencing (NGS) revealed a p.Leu122Arg (c.365 T > G) mutation in the MYOD1 gene, a p.Ala34Gly mutation in the CDKN2A gene, and CDK4 gene amplification. The patient was treated with chemotherapy. She died 17 months after the debut of symptoms. CONCLUSION(S): To our knowledge, this is the first reported case in English literature of an EM with this MYOD1 mutation. We suggest combining PI3K/ATK pathway inhibitors in these cases. NGS should be performed in EMs cases to detect mutations with potential treatment options.

Giant thigh glomus tumor of uncertain malignant potential: Case report with pathologic-radiologic correlation.

INTRODUCTION: Glomus tumors (GT) are rare, benign tumors that arise from glomus bodies and usually develop in digital areas. Extradigital GT are exceptional and thigh location is infrequent. CASE REPORT: We report a case of a GT of the thigh in a 79-year-old male patient that measured 9.5 cm in maximum size. The GT lay above the muscular fascia without infiltrating it. Internal hypervascularity was seen by spectral Doppler ultrasound. Magnetic resonance image showed a heterogeneous mass with hyperintense and hypointense components and internal lobes with liquid-liquid levels. Histopathology revealed a monotonous round-cell proliferation with central nuclei without atypia or mitotic figures, around small-caliber vessels. These cells expressed smooth muscle actin and pericellular collagen IV. GT of uncertain malignant potential was diagnosed. The mass was completely removed. The patient did not experience local relapse nor distant metastasis. CONCLUSION: GT are rare soft tissue tumors whose diagnosis of unusual giant masses in uncommon locations may be delayed and misdiagnosed given the low suspicion.

Immunofluorescence study of the placenta in a case of pemphigoid gestationis: Pathophysiological bases / Estudio de inmunofluorescencia de la placenta a propósito de un caso de penfigoide gestacional: bases fisiopatológicas

Introducción: El herpes gestationis (HG) es una de las principales dermatosis del embarazo que debe ser reconocida y tratada oportunamente ya que se relaciona con un empeoramiento del pronóstico fetal. Aunque se ha investigado la afectación cutánea, hay escasez de estudios morfológicos y funcionales de la placenta en esta patología. Principales síntomas o hallazgos clínicos: Erupción vesicular eritematosa a las 32+1 semanas de gestación. Diagnósticos principales: HG. Intervenciones terapéuticas y resultados: Inmunogammaglobulina en casos graves refractarios a los corticoides por vía oral con desaparición completa de las lesiones. Conclusión: Hasta donde sabemos, este es el primer caso que reporta un análisis detallado de los depósitos de IgG y C3 en la membrana basal de las vellosidades de la placenta mediante un estudio de inmunofluorescencia. Estos hallazgos podrían relacionarse con el ligero mal funcionamiento de la placenta que puede explicar los efectos neonatales adversos.(AU)

Introduction: Pemphigoid gestationis (PG) is one of the main dermatoses of pregnancy that must be recognized and treated promptly, since it is related to worsening of foetal prognosis. Although skin involvement has been investigated, there is a lack of morphological and functional studies of the placenta in this pathology. Main symptoms and/or clinical findings: Erythematous vesicular rash at 32+1 weeks of gestation. Main diagnoses: PG. Therapeutic interventions and results: Immunogammaglobulin in severe cases refractory to oral corticosteroids with complete disappearance of the lesions. Conclusion: To our knowledge, this is the first case to report a detailed analysis of IgG and C3 deposits in the basement membrane of the placental villi by means of an immunofluorescence study. These findings could be related to a slight malfunction of the placenta that may explain the adverse neonatal effects.(AU)

Fibrous hamartoma of infancy. Radiologic-pathologic study of 21 cases: 8 with predominant pseudoangiomatous pattern.

Fibrous hamartoma of infancy (FHI) is a very rare benign soft tissue lesion that principally affects the axilla, trunk, and upper extremities of children younger than 2 years. It is usually cured by local excision. Histologically, these lesions have a triphasic morphology in an organoid pattern: mature adipose tissue, fibroblastic/myofibroblastic trabeculae, and small round cell nests in a myxoid matrix. However, morphologic variants have recently been described. Focal areas with a pseudoangiomatous pattern have been found in some FHI, but few cases with predominant pseudoangiomatous areas have been previously described in the medical literature. We report 21 new cases of FHI, 8 of them with a predominant pseudoangiomatous pattern. Our cases with a predominant pseudoangiomatous pattern did not present specific radiological findings.

Primary intraosseous alveolar soft part sarcoma: Report of two cases with radiologic-pathologic correlation.

Alveolar soft part sarcoma (ASPS) accounts for less than 1 % of all soft tissue sarcomas. ASPS presents a poor prognosis and develops frequent metastases, especially in the lungs, brain and bones. Current therapies, such as surgery, radiotherapy and chemotherapy, are not fully effective and other alternative treatments are currently being studied. ASPS is predominantly found in the deep soft tissues of the lower extremities. To our knowledge, only thirteen primary intraosseous ASPS have been reported in the literature. In this study, we report two new cases of this exceedingly rare entity. Both cases already had multiple metastases since diagnosis; one of them represents the first case of a primary bone ASPS in the ulna and is also the primary intraosseous ASPS with the longest reported case of survival, after having maintained long periods of stabilization despite not having received any systemic treatment.

Calcifying aponeurotic fibroma: Radiologic-pathologic analysis of ten cases and review of the literature.

Calcifying aponeurotic fibroma (CAF) is a very rare benign entity that principally affects the volar fascia, tendons, and aponeuroses of the hands and feet with a peak incidence of between 5 and 15 years, although there have been cases found for a wide age range and at various anatomical sites. We present ten CAF cases; consisting of eight children and two adults. CAF occurred in the extremities in nine of the cases and in the chest wall in one case. CAF ultrasound and radiological findings are nonspecific but may help orientate diagnosis. Magnetic resonance imaging should be performed when there are doubtful cases, when occurring in nontypical sites, and when there are cases of nontypical clinical presentation. Histologically, all cases showed two components, a fibromatosis-like component and a nodular component. Chondroid areas were present in five cases. Calcifications were observed in nine cases. ERG immunostaining showed the same patterns in all the cases; diffuse positivity in pericalcified areas, and patchy positivity in areas away from calcifications. CAF has distinctive histopathological features which should aid in the differential diagnoses with other entities.

Obstetric perinatal and maternal outcomes of monochorionic diamniotic twins following assisted reproductive techniques. Retrospective observational study / Resultados obstétricos perinatales y maternales en gemelos monocoriales diamnióticos conseguidos mediante técnicas de reproducción asistida. Estudio observacional retrospectivo

Introduction: Multiple and specifically monochorionic diamniotic (MCDA) pregnancies are related to maternal and foetal complications. The aim of this study is to evaluate obstetric and perinatal outcomes of MCDA after assisted reproductive techniques (ART). Methods: This is a case-control study comparing 23 MCDA twin pregnancies after ART (ART-MCDA) and 75 spontaneous MCDA (sMCDA). Maternal, obstetric, foetal, and perinatal outcomes variables including maternal age, prematurity, TTTS, sIUGR, TAPS, PROM, and neonatal weight were compared. Results: mean maternal age is higher in the ART-MCDA pregnancies, 38.0±.6 (OR=1.32(1.13–1.53)). Neonates weighing between 1500 and 2500g are more frequent in the sMCDA group and those weighing >2500g in the ART group (OR=0.47(0.22–0.97)). Foetuses born at between 32 and 37 weeks are more frequent in sMCDA pregnancies and those born >37 in the TRA group (OR=0.27(0.09–0.80)). These differences are lost when we adjust the results by maternal age. There were no differences in maternal, obstetric, or foetal complications. Conclusions: ART-MCDA are not associated with a higher number of maternal, obstetric or foetal complications if they are adjusted by maternal age. When they are not adjusted by maternal age, there would be better outcomes such as premature and neonatal weight in the ART group.(AU)

Antecedentes: El incremento de las técnicas de reproducción asistida (TRA) ha supuesto un aumento de las gestaciones gemelares en general, pero también de las monocoriales biamnióticas (MCBA), que se asocian a diversas complicaciones maternofetales. Estas complicaciones están bien estudiadas en gestaciones espontáneas, pero no en aquellas conseguidas mediante una TRA. Objetivo: Comparar la incidencia de complicaciones maternas, fetales, obstétricas y perinatales en gestaciones MCBA conseguidas de forma espontánea frente a aquellas conseguidas mediante TRA. Materiales y métodos: Estudio de casos-controles retrospectivo. Se han analizado 98 gestaciones gemelares MCBA controladas en la Unidad de Medicina Materno-Fetal del Servicio de Obstetricia del Hospital La Paz de Madrid entre los años 2015 y 2020. Resultados: La media de edad de las madres de las gestaciones MCBA conseguidas mediante TRA es mayor (OR=1,32 [1,13-1,53]). Los recién nacidos de peso entre 1.500-2.500g son más frecuentes en las gestaciones MCBA conseguidas de forma espontánea y los de >2.500g en las de TRA (OR=0,47 [0,22–0,97]). Los recién nacidos entre las 32-37 semanas son más frecuentes en las gestaciones gemelares MCBA espontáneas y los recién nacidos de >37 semanas en las de TRA (OR=0,27 [0,09-0,80]). Cuando estos resultados se ajustan por la edad materna dejan de ser estadísticamente significativos. Conclusiones: Las TRA no conllevan un aumento de las complicaciones en las gestaciones MCBA cuando se ajustan los resultados por la edad materna. Si no se ajustasen por la edad materna, las gestaciones MCBA conseguidas mediante TRA tendrían mejores resultados, con menos prematuridad y mayor peso del neonato.(AU)

Ecology of fleas and their hosts in the trifinio of north-east Argentina: first detection of Rickettsia asembonensis in Ctenocephalides felis felis in Argentina.

Fleas are important in public health due to their role as parasites and vectors of pathogens, including Rickettsia. The aim of this study was to evaluate the diversity, abundance and prevalence of fleas and the presence of Rickettsia in the trifinio of north-east Argentina. Fleas from household and synanthropic animals were obtained from urban and periurban areas. They were taxonomically identified and samples of 227 fleas in 86 pools were analysed by polymerase chain reaction targeting the gltA and ompB genes of Rickettsia spp. The study revealed that Ctenocephalides felis felis was dominant on dogs, cats and opossums, with higher prevalence in the periurban area. The Shannon-Wiener and Morisita-Horn indices expressed differences in the diversity and similarity values of the absolute abundances of the species between the areas compared. DNA amplifications revealed 30.8% C. f. felis pools positive for Rickettsia spp. Phylogenetic analysis showed that the haplotype obtained was identical to Rickettsia asembonensis from Peru and Brazil. This is the first detection in Argentina of R. asembonensis that infects C. f. felis, and we emphasize the importance of conducting research from a 'One Health' perspective on the role of opossums and rodents in the integration of the transmission cycles of rickettsial bacteria.

First Evidence of Akodon-Borne Orthohantavirus in Northeastern Argentina.

Orthohantaviruses (genus Orthohantavirus, family Hantaviridae) are the etiologic agents of Hantavirus Pulmonary Syndrome in the Americas. In South America, orthohantaviruses are highly diverse and are hosted by sigmodontine rodents (subfamiliy Sigmodontinae, family Cricetidae), an also diverse group of rodents. The aims of this work were to (1) identify orthohantavirus hosts and (2) to study the spatial and temporal variations in the prevalence of infection and their associations with community, environmental and individual characteristics, in different environments of Misiones province, northeastern Argentina. Live-capture sessions were carried out during two years in different land uses, with a trapping effort of 31,653 trap nights. We captured 719 individuals from the species Akodon montensis, Rattus rattus, Mus musculus, Calomys tener, Thaptomys nigrita, Oligoryzomys nigripes, Euryoryzomys russatus, Oligoryzomys flavescens, Brucepattersonius sp., and Juliomys pictipes. Antibodies against orthohantavirus were detected in Akodon montensis in one natural protected and one periurban areas, and it was the most abundant species in almost every study sites. We observed the presence of spatial focality of orthohantavirus infection and a positive association with host abundance suggesting the existence of a threshold density. At the individual level, large, reproductively active, and male individuals were more likely to have antibodies against orthohantavirus. This is the first record of orthohantavirus infection in A. montensis in Argentina, which shows the importance of investigations about emerging diseases.