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Fibrous histiocytoma is a benign soft-tissue neoplasm that commonly involves the dermis. It is rare in the oral cavity. This lesion creates a diagnostic dilemma due to its nonspecific clinical appearance and microscopic similarities with other benign fibrous tissue lesions. Microscopically, it shows the proliferation of both spindle-shaped fibroblasts and histiocytes. Surgical excision is the treatment of choice with a good prognosis. The purpose of this paper is to report a rare case of gingival benign fibrous histiocytoma occurring in an 11-year-old female patient. The diagnosis of this lesion is based on combined clinical, histopathological, and immunohistochemical features.

Abstract Necrobiotic xanthogranuloma (NXG) is a rare non‐Langerhans cell histiocytosis associated with paraproteinemia. Skin lesions of NXG are difficult to treat and various therapies have been evaluated with inconsistent results. A therapeutic standard has not been established. We report on a patient severely affected by mutilating skin and ocular lesions as well as lung infiltrates of necrobiotic xanthogranuloma. After failure of several previous therapies including dapsone and adalimumab, lesions significantly improved during therapy with intravenous immunoglobulins (IVIg). IVIg are an effective treatment option to evaluate in NXG.

Hematopoietic progenitors are enriched in the endocardial cushion and contribute, in a Nkx2-5-dependent manner, to tissue macrophages required for the remodeling of cardiac valves and septa. However, little is known about the molecular mechanism of endocardial-hematopoietic transition. In the current study, we identified the regulatory network of endocardial hematopoiesis. Signal network analysis from scRNA-seq datasets revealed that genes in Notch and retinoic acid (RA) signaling are significantly downregulated in Nkx2-5-null endocardial cells. In vivo and ex vivo analyses validate that the Nkx2-5-Notch axis is essential for the generation of both hemogenic and cushion endocardial cells, and the suppression of RA signaling via Dhrs3 expression plays important roles in further differentiation into macrophages. Genetic ablation study revealed that these macrophages are essential in cardiac valve remodeling. In summary, the study demonstrates that the Nkx2-5/Notch/RA signaling plays a pivotal role in macrophage differentiation from hematopoietic progenitors.

Histiocytic Sarcoma (HS) is an extremely rare haematolymphoid neoplasm that exhibits morphological and immunophenotypic features indicative of histiocytic differentiation. In most cases, it is misdiagnosed as Diffuse Large B-Cell Lymphoma (DLBCL) or anaplastic large cell lymphoma. HS is a diagnosis of exclusion, necessitating extensive immunophenotypic analysis to finalise the diagnosis. Hereby, authors present a case series of five cases diagnosed as HS based on histomorphology and an extensive Immunohistochemistry (IHC) panel. A total of five cases reported as HS over a five-year period (2018 to 2023) were diagnosed at the Department of Pathology. All demographic and clinical data, as well as treatment history, were collected from the patients and their family members. Paraffin-embedded blocks were retrieved from the archive, and routine Haematoxylin and Eosin (H&E) and special stains like Periodic Acid-Schiff (PAS) were performed. Microscopy revealed sheets of round to oval tumour cells with small round nuclei, inconspicuous nucleoli, and moderately microvacuolated cytoplasm. An extended IHC panel was applied to confirm the microscopic findings. All five cases exhibited intense immunoreactivity for Leukocyte Common Antigen (LCA) and showed strong positivity for the histiocytic marker CD68, while CD163 demonstrated variable cytoplasmic positivity. Dako R antibody at a dilution of 1:100 was used for the IHC analysis. This case series aims to highlight the importance of clinical, radiological, histological, and immunohistochemical properties of this rare neoplasm for early diagnosis and proper management.

Histiocytic Sarcoma (HS) is an extremely rare haematolymphoid neoplasm that exhibits morphological and immunophenotypic features indicative of histiocytic differentiation. In most cases, it is misdiagnosed as Diffuse Large B-Cell Lymphoma (DLBCL) or anaplastic large cell lymphoma. HS is a diagnosis of exclusion, necessitating extensive immunophenotypic analysis to finalise the diagnosis. Hereby, authors present a case series of five cases diagnosed as HS based on histomorphology and an extensive Immunohistochemistry (IHC) panel. A total of five cases reported as HS over a five-year period (2018 to 2023) were diagnosed at the Department of Pathology. All demographic and clinical data, as well as treatment history, were collected from the patients and their family members. Paraffin-embedded blocks were retrieved from the archive, and routine Haematoxylin and Eosin (H&E) and special stains like Periodic Acid-Schiff (PAS) were performed. Microscopy revealed sheets of round to oval tumour cells with small round nuclei, inconspicuous nucleoli, and moderately microvacuolated cytoplasm. An extended IHC panel was applied to confirm the microscopic findings. All five cases exhibited intense immunoreactivity for Leukocyte Common Antigen (LCA) and showed strong positivity for the histiocytic marker CD68, while CD163 demonstrated variable cytoplasmic positivity. Dako R antibody at a dilution of 1:100 was used for the IHC analysis. This case series aims to highlight the importance of clinical, radiological, histological, and immunohistochemical properties of this rare neoplasm for early diagnosis and proper management. [ABSTRACT FROM AUTHOR]

Summary: Histiocytic neoplasms are diverse clonal haematopoietic disorders, and clinical disease is mediated by tumorous infiltration as well as uncontrolled systemic inflammation. Individual subtypes include Langerhans cell histiocytosis (LCH), Rosai–Dorfman–Destombes disease (RDD) and Erdheim–Chester disease (ECD), and these have been characterized with respect to clinical phenotypes, driver mutations and treatment paradigms. Less is known about patients with mixed histiocytic neoplasms (MXH), that is two or more coexisting disorders. This international collaboration examined patients with biopsy‐proven MXH with respect to component disease subtypes, oncogenic driver mutations and responses to conventional (chemotherapeutic or immunosuppressive) versus targeted (BRAF or MEK inhibitor) therapies. Twenty‐seven patients were studied with ECD/LCH (19/27), ECD/RDD (6/27), RDD/LCH (1/27) and ECD/RDD/LCH (1/27). Mutations previously undescribed in MXH were identified, including KRAS, MAP2K2, MAPK3, non‐V600‐BRAF, RAF1 and a BICD2‐BRAF fusion. A repeated‐measure generalized estimating equation demonstrated that targeted treatment was statistically significantly (1) more likely to result in a complete response (CR), partial response (PR) or stable disease (SD) (odds ratio [OR]: 17.34, 95% CI: 2.19–137.00, p = 0.007), and (2) less likely to result in progression (OR: 0.08, 95% CI: 0.03–0.23, p < 0.0001). Histiocytic neoplasms represent an entity with underappreciated clinical and molecular diversity, poor responsiveness to conventional therapy and exquisite sensitivity to targeted therapy. [ABSTRACT FROM AUTHOR]

Fibrous histiocytoma is a benign soft-tissue neoplasm that commonly involves the dermis. It is rare in the oral cavity. This lesion creates a diagnostic dilemma due to its nonspecific clinical appearance and microscopic similarities with other benign fibrous tissue lesions. Microscopically, it shows the proliferation of both spindle-shaped fibroblasts and histiocytes. Surgical excision is the treatment of choice with a good prognosis. The purpose of this paper is to report a rare case of gingival benign fibrous histiocytoma occurring in an 11-year-old female patient. The diagnosis of this lesion is based on combined clinical, histopathological, and immunohistochemical features. [ABSTRACT FROM AUTHOR]

Abstract Neurologic Rosai–Dorfman disease (RDD) is a rare type of non-Langerhans cell histiocytosis that affects the central nervous system. Most neurologic RDDs grow like meningiomas, have clear boundaries, and can be completely resected. However, a few RDDs are invasive and aggressive, and no effective treatment options are available because the molecular mechanisms involved remain unknown. Here, we report a case of deadly and glucocorticoid-resistant neurologic RDD and explore its possible pathogenic mechanisms via single-cell RNA sequencing. First, we identified two distinct but evolutionarily related histiocyte subpopulations (the C1Q+ and SPP1+ histiocytes) that accumulated in the biopsy sample. The expression of genes in the KRAS signaling pathway was upregulated, indicating gain-of-function of KRAS mutations. The C1Q+ and SPP1+ histiocytes were highly differentiated and arrested in the G1 phase, excluding the idea that RDD is a lympho-histio-proliferative disorder. Second, although C1Q+ histiocytes were the primary RDD cell type, SPP1+ histiocytes highly expressed several severe inflammation-related and invasive factors, such as WNT5A, IL-6, and MMP12, suggesting that SPP1+ histiocytes plays a central role in driving the progression of this disease. Third, oligodendrocytes were found to be the prominent cell type that initiates RDD via MIF and may resist glucocorticoid treatment via the MDK and PTN signaling pathways. In summary, in this case, we report a rare presentation of neurologic RDD and provided new insight into the pathogenic mechanisms of progressive neurologic RDD. This study will also offer evidence for developing precision therapies targeting this complex disease.

Abstract The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble α-synuclein aggregates in their olfactory bulbs (OB). Subjects affected by a SARS-CoV-2-linked illness (COVID-19) also frequently experience hyposmia. We previously postulated that microglial activation as well as α-synuclein and tau misprocessing can occur during host responses following microbial encounters. Using semiquantitative measurements of immunohistochemical signals, we examined OB and olfactory tract specimens collected serially at autopsies between 2020 and 2023. Deceased subjects comprised 50 adults, which included COVID19 + patients (n = 22), individuals with Lewy body disease (e.g., PD; dementia with Lewy bodies (n = 6)), Alzheimer disease (AD; n = 3), and other neurodegenerative disorders (e.g., progressive supranuclear palsy (n = 2); multisystem atrophy (n = 1)). Further, we included neurologically healthy controls (n = 9), and added subjects with an inflammation-rich brain disorder as neurological controls (NCO; n = 7). When probing for microglial and histiocytic reactivity in the anterior olfactory nuclei (AON) by anti-CD68 immunostaining, scores were consistently elevated in NCO and AD cases. In contrast, microglial signals on average were not significantly altered in COVID19 + patients relative to healthy controls, although anti-CD68 reactivity in their OB and tracts declined with progression in age. Mild-to-moderate increases in phospho-α-synuclein and phospho-tau signals were detected in the AON of tauopathy- and synucleinopathy-afflicted brains, respectively, consistent with mixed pathology, as described by others. Lastly, when both sides were available for comparison in our case series, we saw no asymmetry in the degree of pathology of the left versus right OB and tracts. We concluded from our autopsy series that after a fatal course of COVID-19, microscopic changes in the rostral, intracranial portion of the olfactory circuitry -when present- reflected neurodegenerative processes seen elsewhere in the brain. In general, microglial reactivity correlated best with the degree of Alzheimer’s-linked tauopathy and declined with progression of age in COVID19 + patients.

Abstract Background The “C group” of the histiocytic disorders is characterized by non-Langerhans-cell histiocytic lesions in the skin, mucosal surfaces, or both, out of which Juvenile xanthogranuloma (JXG) is the most common typically affecting the skin. The eye is the most common extra-cutaneous site of JXG., we aim at providing our clinical and histopathological experience with this group of diseases including the adult-onset xanthogranuloma (AXG). Methods This is a retrospective cohort study of all patients with the tissue diagnosis of ocular and periocular cutaneous and mucocutaneous non-LCH disorders who presented to us over a period of 25 years (January 1993 to December 2018). Results Twenty patients were diagnosed as “Group C” disease with an age range of 2 months-60.9 years. Eleven patients were females (55%) and nine were males (45%). The involvement was mostly unilateral in 80.9%. All cases fell into the xanthogranuloma family with 11 JXG patients, 8 AXG patients of skin and ocular surface, and one patient with solitary reticulohistiocytoma (SRH). The clinical site of involvement in JXG was primarily in the eyelid in 5 patients (45%), ocular surface lesions in 2 (18%), iris in 2 (18%), choroidal and bilateral orbital lesions in 1 patient each (9%). The group of AXG, presented equally with eyelid lesions in 4/8 and ocular surface lesions in 4/8. The non-Langerhans’ histiocytic infiltrate showed supportive immunohistochemical staining properties (reactive to CD68 marker and negative to S-100 and langerin markers). Conclusion Among the rare histiocytic disorders, xanthogranulomatosis is the commonest and has wide clinical manifestations. Accurate diagnosis needs to be supported by typical histopathological findings. JXG was the commonest in our study with relatively older mean age at presentation and frequent eyelid rather than iris involvement. AXG is often confused with xanthelasma when involving the eyelids with corneal limbal involvement is relatively frequent.

Neurofibromatosis type 1 (NF1) is an inherited tumor syndrome caused by heterozygous germline mutations in the NF1 gene, occurring in approximately 1/2600 individuals. A subset of patients with neurofibromatosis type 1 (NF1) develop juvenile xanthogranulomas (JXGs), a non-Langerhans cell histiocytosis, and some of these patients also develop juvenile myelomonocytic leukemia (JMML).Yet, these associations are poorly delineated.JXG is a benign proliferation of non-Langerhans cells histiocytes characterized by small yellow/brown papulonodules ranging from 1-20 mm in size. JMML is a mixed myeloproliferative-myelodysplastic disorder that affects children, most often before age 6.4. The first and only systematic review on this described therisk of developing JMML 20 to 30 times higher in patients with NF1 with JXG lesions compared to those without JXG. Since then, mostly isolated case reports have either refuted or confirmed this triple association.

Herein, we present a patient with a lipidized fibrous histiocytoma, an underrecognized variant of dermatofibroma (cutaneous fibrous histiocytoma). Our patient presented with a nodule on the ankle that showed foamy histiocytes and hyalinized collagen bundles on histology. This case highlights a classic presentation and features of lipidized fibrous histiocytoma, raising further awareness of this distinctive variant of dermatofibroma that should be distinguished from xanthoma and xanthogranuloma.

Neurologic Rosai–Dorfman disease (RDD) is a rare type of non-Langerhans cell histiocytosis that affects the central nervous system. Most neurologic RDDs grow like meningiomas, have clear boundaries, and can be completely resected. However, a few RDDs are invasive and aggressive, and no effective treatment options are available because the molecular mechanisms involved remain unknown. Here, we report a case of deadly and glucocorticoid-resistant neurologic RDD and explore its possible pathogenic mechanisms via single-cell RNA sequencing. First, we identified two distinct but evolutionarily related histiocyte subpopulations (the C1Q+ and SPP1+ histiocytes) that accumulated in the biopsy sample. The expression of genes in the KRAS signaling pathway was upregulated, indicating gain-of-function of KRAS mutations. The C1Q+ and SPP1+ histiocytes were highly differentiated and arrested in the G1 phase, excluding the idea that RDD is a lympho-histio-proliferative disorder. Second, although C1Q+ histiocytes were the primary RDD cell type, SPP1+ histiocytes highly expressed several severe inflammation-related and invasive factors, such as WNT5A, IL-6, and MMP12, suggesting that SPP1+ histiocytes plays a central role in driving the progression of this disease. Third, oligodendrocytes were found to be the prominent cell type that initiates RDD via MIF and may resist glucocorticoid treatment via the MDK and PTN signaling pathways. In summary, in this case, we report a rare presentation of neurologic RDD and provided new insight into the pathogenic mechanisms of progressive neurologic RDD. This study will also offer evidence for developing precision therapies targeting this complex disease. [ABSTRACT FROM AUTHOR]

The majority of patients with Parkinson disease (PD) experience a loss in their sense of smell and accumulate insoluble α-synuclein aggregates in their olfactory bulbs (OB). Subjects affected by a SARS-CoV-2-linked illness (COVID-19) also frequently experience hyposmia. We previously postulated that microglial activation as well as α-synuclein and tau misprocessing can occur during host responses following microbial encounters. Using semiquantitative measurements of immunohistochemical signals, we examined OB and olfactory tract specimens collected serially at autopsies between 2020 and 2023. Deceased subjects comprised 50 adults, which included COVID19 + patients (n = 22), individuals with Lewy body disease (e.g., PD; dementia with Lewy bodies (n = 6)), Alzheimer disease (AD; n = 3), and other neurodegenerative disorders (e.g., progressive supranuclear palsy (n = 2); multisystem atrophy (n = 1)). Further, we included neurologically healthy controls (n = 9), and added subjects with an inflammation-rich brain disorder as neurological controls (NCO; n = 7). When probing for microglial and histiocytic reactivity in the anterior olfactory nuclei (AON) by anti-CD68 immunostaining, scores were consistently elevated in NCO and AD cases. In contrast, microglial signals on average were not significantly altered in COVID19 + patients relative to healthy controls, although anti-CD68 reactivity in their OB and tracts declined with progression in age. Mild-to-moderate increases in phospho-α-synuclein and phospho-tau signals were detected in the AON of tauopathy- and synucleinopathy-afflicted brains, respectively, consistent with mixed pathology, as described by others. Lastly, when both sides were available for comparison in our case series, we saw no asymmetry in the degree of pathology of the left versus right OB and tracts. We concluded from our autopsy series that after a fatal course of COVID-19, microscopic changes in the rostral, intracranial portion of the olfactory circuitry -when present- reflected neurodegenerative processes seen elsewhere in the brain. In general, microglial reactivity correlated best with the degree of Alzheimer's-linked tauopathy and declined with progression of age in COVID19 + patients. [ABSTRACT FROM AUTHOR]

Background: The "C group" of the histiocytic disorders is characterized by non-Langerhans-cell histiocytic lesions in the skin, mucosal surfaces, or both, out of which Juvenile xanthogranuloma (JXG) is the most common typically affecting the skin. The eye is the most common extra-cutaneous site of JXG., we aim at providing our clinical and histopathological experience with this group of diseases including the adult-onset xanthogranuloma (AXG). Methods: This is a retrospective cohort study of all patients with the tissue diagnosis of ocular and periocular cutaneous and mucocutaneous non-LCH disorders who presented to us over a period of 25 years (January 1993 to December 2018). Results: Twenty patients were diagnosed as "Group C" disease with an age range of 2 months-60.9 years. Eleven patients were females (55%) and nine were males (45%). The involvement was mostly unilateral in 80.9%. All cases fell into the xanthogranuloma family with 11 JXG patients, 8 AXG patients of skin and ocular surface, and one patient with solitary reticulohistiocytoma (SRH). The clinical site of involvement in JXG was primarily in the eyelid in 5 patients (45%), ocular surface lesions in 2 (18%), iris in 2 (18%), choroidal and bilateral orbital lesions in 1 patient each (9%). The group of AXG, presented equally with eyelid lesions in 4/8 and ocular surface lesions in 4/8. The non-Langerhans' histiocytic infiltrate showed supportive immunohistochemical staining properties (reactive to CD68 marker and negative to S-100 and langerin markers). Conclusion: Among the rare histiocytic disorders, xanthogranulomatosis is the commonest and has wide clinical manifestations. Accurate diagnosis needs to be supported by typical histopathological findings. JXG was the commonest in our study with relatively older mean age at presentation and frequent eyelid rather than iris involvement. AXG is often confused with xanthelasma when involving the eyelids with corneal limbal involvement is relatively frequent. [ABSTRACT FROM AUTHOR]

Rosai-Dorfman Disease is a rare benign disorder involving overproduction of immune cells, causing swollen lymph nodes and, in rare cases, the sternum. The sternal involvement may cause chest pain and masses. Diagnosis is confirmed through clinical examination, biopsy, and imaging. Treatment options may include surgery, radiation, or steroids. In this case study, we present an unusual example of extranodal Rosai-Dorfman Disease involving the sternum, bilateral clavicles and first three ribs, and pectoral muscle with no associated lymphadenopathy or systemic symptoms in a 57-year-old female. The etiology, pathology, immunohistochemistry, imaging findings, and treatment options of this unique disease are discussed. [ABSTRACT FROM AUTHOR]

Langerhans cell histiocytosis (LCH) is a histiocytic neoplasm characterized by the abnormal proliferation of Langerhans cells. Bone marrow (BM) involvement is associated with high-risk disease and poor survival. Although BM involvement is particularly uncommon, no reported cases of LCH with BM infiltration have been documented in Latin America until now. The aim of this report is to highlight the clinical, hematological, and BM findings of two cases of LCH with BM infiltration, providing insights that may aid in detecting suspected patients. We present two cases of LCH with BM infiltration. One case involved a 23-month-old male patient, and the other a 16-month-old female patient. Common clinical findings in both cases included hepatosplenomegaly and fever. Hematological findings revealed anemia in both cases. The key diagnostic tool was the BM biopsy, which revealed histiocyte nests with characteristic morphology, CD1a-positive cells, increased eosinophils, and reactive paratrabecular lymphocytes. This report underscores the significance of clinical profiles in predicting BM infiltration in LCH. The presence of histiocyte nests displaying the characteristic morphology of Langerhans cells, accompanied by an elevation in eosinophils, indicates bone marrow involvement. Furthermore, the demonstration of CD1a-positive cells through immunohistochemistry serves as a crucial diagnostic tool.

Summary: Since the publication in 2017 of the revised 4th Edition of the World Health Organization (WHO) classification of haematolymphoid tumours, here referred to as WHO‐HAEM4, significant clinicopathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining the diagnostic criteria of several diseases, upgrading entities previously defined as provisional and identifying new entities. This process has resulted in two recent classification proposals of lymphoid neoplasms: the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO‐HAEM5). In this paper, we review and compare the two classifications in terms of diagnostic criteria and entity definition, focusing on T‐cell lymphomas and histiocytic/dendritic cell tumours. Moreover, we update the genetic data of the various pathological entities. The main goal is to provide a tool to facilitate the work of the pathologists, haematologists and researchers involved in the diagnosis and treatment of these haematological malignancies. [ABSTRACT FROM AUTHOR]

Summary: To calculate the prevalence of sinonasal and ear involvement in an Erdheim‐Chester disease (ECD) population, to describe the different ear, nose and throat (ENT) manifestations and to study the association between ENT involvement, other organ involvement, and BRAF mutations. We led a retrospective monocentric study in the national referral center for ECD. One hundred and sixty‐two patients with ECD and ENT data were included between January 1, 1980 and December 31, 2020. Ear and nose clinical and radiological findings were noted. We described and studied the prevalence of ENT involvement in ECD population. The association between sinonasal and ear involvement, other organ involvement, and BRAF mutations was calculated. The prevalence of ENT manifestations is around 45%. No clinical rhinologic or otologic signs were specific to ECD. Sinus imaging was abnormal in 70% of cases. A bilateral maxillary sinus frame osteosclerosis was highly specific of ECD. Associations were found between the sinus MRI imaging type and BRAF status, central nervous system involvement, cerebellum involvement and xanthelasma. Sinonasal or ear involvement is frequent in ECD and has specific imaging features for sinuses. Trial registration: #2011‐A00447‐34. [ABSTRACT FROM AUTHOR]

• Xanthogranulomatous conditions may present as lipid-rich periorbital lesions. • Xanthogranuloma is characterized by lipid-laden Touton giant cells. • Systemic disease can be life-threatening; multidisciplinary work-up is warranted. This report describes an unusual and diagnostically challenging case of subcutaneous soft tissue xanthogranulomas of bilateral orbits of a 58-year-old female patient seen in a private oculoplastics practice. Accurate and timely diagnosis is crucial in xanthogranulomatous diseases so that any systemic manifestations can be identified and addressed in a multidisciplinary fashion. Periorbital xanthogranuloma is a frequent early manifestation of adult xanthogranulomatous disease, and its association with life-threatening systemic disease requires accurate diagnosis and prompt work-up. This case describes an otherwise asymptomatic patient who presented with bilateral orbital masses causing visually significant ptosis, initially diagnosed as soft tissue xanthomas, and later identified as xanthogranulomas. It is important for physicians of all fields, from primary care to surgical subspecialty, to be aware that xanthogranulomatous disease may first present as periorbital lesions and/or orbital masses, and that further work-up for vision and life-threatening systemic disease is warranted. [ABSTRACT FROM AUTHOR]

Background: Mycobacterial spindle cell pseudotumor (MSCP) represents an uncommon tumor-like proliferation associated with nontuberculous mycobacterial infection, i.e., M. avium intracellulare, affecting primarily the lymph nodes of immunocompromised men in their 5th decade. Involvement of the nasal cavity by MSCP is exceedingly rare with only 3 well-documented examples in the literature. Methods: A 74-year-old, HIV-negative, man presented with a 0.5-cm nodule of the left nasal cavity clinically presenting as a "nasal polyp." His medical history was significant for colonic adenocarcinoma, cutaneous basal cell carcinoma, and chronic lymphocytic leukemia (CLL) transforming to B-cell prolymphocytic leukemia, responsive to chemotherapy. The patient was diagnosed with prostatic adenocarcinoma treated with radiotherapy two months before the nasal lesion was detected. No lymph node enlargement, pulmonary involvement or hepatosplenomegaly were noticed. The nasal nodule was surgically excised and histopathologically examined to rule out metastatic disease or CLL relapse. Results: Microscopically, the lesion comprised a well-circumscribed, monotonous, spindle cell population in a vaguely storiform arrangement mixed with a heavy infiltrate of neutrophils and sparse lymphocytes. The spindle cells featured finely granular rich eosinophilic cytoplasm with rounded, oval to epithelioid, or elongated nuclei with vesicular chromatin and one or two distinct nucleoli. The lesional cells lacked overt cytologic atypia and showed occasional regular mitoses. The surface epithelium was intact or focally ulcerated. By immunohistochemistry, the spindle cell population stained strongly and diffusely for CD68 and was negative for AE1/AE3, SMA, CD34, and PSA. CD3 highlighted scattered lymphocytes. Ziehl–Neelsen stain disclosed numerous intracytoplasmic acid-fast bacilli. A diagnosis of MSCP was rendered. No recurrences were observed during a 24-month follow-up period. Conclusion: Although exceptionally rare, MSCP should be considered in the differential diagnosis of nodular lesions of the nasal cavity that are characterized microscopically by marked spindle cell proliferation in a vague storiform pattern, admixed with a lymphocytic or mixed inflammatory infiltrate. A negative medical history for HIV infection and medication-induced immunosuppression should not preclude a diagnosis of MSCP, particularly in extranodal sites. Once the diagnosis is established, prognosis appears to be excellent for nasal MSCP following conservative surgical excision. [ABSTRACT FROM AUTHOR]

First described in 1930 as a lipoid granulomatosis, Erdheim-Chester disease (ECD) is a rare histiocytosis encompassing a group of disorders caused by overproduction of histiocytes, a subtype of white blood cells. This disease most commonly involves the bones and can affect organs in the abdomen; however, biliary involvement is rarely reported. We report a case of ECD with biliary involvement, which rendered it difficult to radiologically distinguish ECD from immunoglobulin G4-related disease.

Inflammatory leiomyosarcoma (LMS) is a newly included rare tumor entity in the group of smooth muscle tumors in the recent WHO classification. Recent studies have shown skeletal muscle expression within this tumor and its proximity with histiocyte-rich rhabdomyoblastic tumor (HRRT). A 17-year-old male presented with a soft tissue lump over the back of his neck of one-year duration. Radiologically, a lesion measuring 5.9 cm in the largest dimension was seen, extending from the skull base up to the C2 vertebral level, abutting the occipital bone. The initial biopsy was reported as a fibrohistiocytic tumor at the referring laboratory. A microscopic review of the sections from the initial biopsy and subsequent resection revealed a well-circumscribed, cellular tumor composed of plump spindle and polygonal-shaped tumor cells with relatively bland nuclei, moderate to abundant eosinophilic cytoplasm and numerous interspersed histiocytes, including foam cells and lymphocytes. Immunohistochemically, the tumor cells were positive for desmin, MYOD1 and SMA, focally positive for myogenin, while negative for h-caldesmon, SOX10 and S100P. A diagnosis of inflammatory leiomyosarcoma/HRRT was offered. Subsequently, the tumor was tested for MYOD1 (L122R) mutation and was found to be negative. The patient underwent adjuvant radiation therapy and is free-of-disease at 12 months post-treatment. This case constitutes an extremely rare case of an inflammatory LMS/HRRT, identified in the neck region. This tumor should be differentiated from its close mimics, such as a spindle cell/sclerosing rhabdomyosarcoma, as the latter is treated more aggressively, including with chemotherapy, given its relatively poor prognosis.

Erdheim-Chester disease (ECD) as a rare non-Langerhans histiocytosis has various clinical manifestations. It is characterized histologically by infiltration of every organ, more commonly bone, retroperitoneum, cardiovascular and CNS systems with foamy, lipid -laden macrophage. Pancreatic involvement as a manifestation of this uncommon disease has very rarely been reported. Here we report a 73-year-old woman with ECD and pancreas involvement in CT, MRI and PET scans. We also aim to increase radiologist knowledge about considering ECD as a differential diagnosis for pancreas mass in the appropriate clinical situation.

Histiocytic Sarcoma (HS) is a rare malignant neoplasm characterised by the neoplastic proliferation of cells showing morphological and immunophenotypic features of mature histiocytes. Majority of the reported cases present in extranodal sites, such as the head and neck, thyroid, duodenum, small intestine, colon, urinary bladder, spleen, and leptomeninges. This report documents a case of primary involvement of the salivary gland by HS. A 77-year-old male patient presented with a firm swelling in the left submandibular region for the last three months. Multiple lymph nodes, along with the presence of lung and liver nodules, were seen. Thus the final diagnosis of HS was made based on histopathology and IHC. Palliative chemotherapy was given to the patient, responded well, and has been well for the last year. The present study is probably the first case of HS involving the submandibular gland.

Introduction: Rosai-Dorfman Disease (RDD), an entity first described in 1969 is a rare disorder characterized by proliferation of histiocytes that primarily occurs in lymph nodes. In the breast, RDD is extremely rare. Although the disease typically has a slow progressive nature, it is important to recognize it as it can mimic malignancy. Case presentation: We present a case of a 17-year-old male with no significant past medical history who presented to the pediatric surgery office for evaluation of a left-sided breast mass that was suspicious for malignancy. The ultrasound findings were non-diagnostic at the time. Although further workup of this mass may have been achieved by CT scan, MRI or core biopsy, the decision was made to proceed with upfront surgical resection for both diagnostic and therapeutic purposes. Final immunohistochemistry of the mass revealed atypical large histiocytes positive for CD68 with co-expression of S100 consistent with RDD. At the time of publication, the patient is alive and well. He has not received any further therapy for RDD and there were no signs of recurrence. Conclusion: The diagnosis of Rosai-Dorfman disease can be quite challenging. Given the variable presentation and nonspecific imaging findings, definitive diagnosis relies on histopathologic findings. Pediatric patients with unifocal RDD involving the breast can be effectively treated with surgical resection safely as both a diagnostic and therapeutic option.

A 7-year-old captive female jaguar (Panthera onca) was presented with a 7-day history of dyspnoea and weight loss. Clinical examination revealed hepatomegaly and elevated serum alanine aminotransferase activity. Pulmonary ultrasonography revealed comet-tail images and an alveolar pattern was detected on thoracic radiography. Due to the poor prognosis, the jaguar was euthanized after 10 days. At necropsy, the main gross findings were hepatomegaly, splenomegaly and multifocal to coalescent, slightly elevated grey areas in the lungs. Histological examination revealed neoplastic proliferation of pleomorphic histiocytes arranged in cohesive sheets in the lungs, liver, spleen, kidneys and lymph nodes. Neoplastic cells had intense immunolabelling for vimentin and ionized calcium-binding adaptor molecule 1, and were immunonegative for pancytokeratin, E-cadherin, CD20, CD3 and CD79α. These findings were compatible with a systemic histiocytic disorder, distinct from any well-defined histiocytic proliferative disease in domestic animals. [ABSTRACT FROM AUTHOR]

Introduction. Niemann–Pick disease type B is an autosomal recessive disease caused by sphingomyelinase deficiency resulting in sphingomyelin accumulation in macrophages of various organs. Visceral involvement includes spleen enlargement, thrombocytopenia, dyslipidemia, sphingomyelin deposition in lung and liver, and bleeding risk. This is a rare disease and literature data about pregnancy in this setting are scarce. We present two favorable pregnancy outcomes in a patient with Niemann–Pick disease type B along with the review of the literature. Case outline. At the time of the first intended pregnancy, the patient was 34 years old. She had an extremely enlarged spleen, mild restrictive pulmonary disorder, hyperlipoproteinemia type IIb, thrombocytopenia with impaired aggregation tests. Cesarean section was indicated. She was prepared for delivery with platelet concentrates and prophylactic use of antibiotics. In the 36th week of gestation, a Cesarean section without complications was performed. The newborn’s anthropometric parameters were BW 2490, BL 47 cm, HC 32 cm, and Apgar score was 7/8. The infant’s development was normal. Three years later, in the second wanted pregnancy, the same examinations were done. The planned Cesarean section was done without complication after the same procedures, including prophylactic use of antibiotics and platelet concentrates, and a healthy female child was born. Conclusion. A multidisciplinary approach in female patients who suffer from lysosomal storage disease such as Niemann–Pick disease type B is essential and a favorable course is possible despite all risks.

Inflammatory leiomyosarcoma (LMS) is a newly included rare tumor entity in the group of smooth muscle tumors in the recent WHO classification. Recent studies have shown skeletal muscle expression within this tumor and its proximity with histiocyte-rich rhabdomyoblastic tumor (HRRT). A 17-year-old male presented with a soft tissue lump over the back of his neck of one-year duration. Radiologically, a lesion measuring 5.9 cm in the largest dimension was seen, extending from the skull base up to the C2 vertebral level, abutting the occipital bone. The initial biopsy was reported as a fibrohistiocytic tumor at the referring laboratory. A microscopic review of the sections from the initial biopsy and subsequent resection revealed a well-circumscribed, cellular tumor composed of plump spindle and polygonal-shaped tumor cells with relatively bland nuclei, moderate to abundant eosinophilic cytoplasm and numerous interspersed histiocytes, including foam cells and lymphocytes. Immunohistochemically, the tumor cells were positive for desmin, MYOD1 and SMA, focally positive for myogenin, while negative for h-caldesmon, SOX10 and S100P. A diagnosis of inflammatory leiomyosarcoma/HRRT was offered. Subsequently, the tumor was tested for MYOD1 (L122R) mutation and was found to be negative. The patient underwent adjuvant radiation therapy and is free-of-disease at 12 months post-treatment. This case constitutes an extremely rare case of an inflammatory LMS/HRRT, identified in the neck region. This tumor should be differentiated from its close mimics, such as a spindle cell/sclerosing rhabdomyosarcoma, as the latter is treated more aggressively, including with chemotherapy, given its relatively poor prognosis. [ABSTRACT FROM AUTHOR]

A 16‐year‐old female spayed domestic shorthaired cat was examined for lameness and a mass on the fourth digit of the right hindlimb. Cytologic examination of an aspirate of the mass revealed large discrete cells admixed with low numbers of well‐granulated mast cells. The discrete cells contained single to many variably sized light pink to purple granules in their cytoplasm and had pleomorphic nuclei, with intranuclear cytoplasmic inclusions. Karyomegalic, binucleated and multinucleated cells were seen. Histologic examination of formalin‐fixed sections of the excised mass showed a mildly infiltrative, unencapsulated, multinodular dermal mass that extended into the subcutis and consisted of similar discrete cells. On immunohistochemical staining, the tumor cells expressed ionized calcium‐binding adapter molecule 1 (Iba1) and CD18. The tumor cells did not express CD3, CD20, CD117, pancytokeratin (AE1/AE3), melanoma antigen (Melan‐A), multiple myeloma oncogene‐1 (MUM1), melanoma‐associated antigen (PNL‐2), and S‐100. Low numbers of tumor cells expressed CD204 and protein gene product 9.5 (PGP9.5). Granules were variably positive for Periodic‐acid Schiff (PAS) and Alcian blue. On transmission electron microscopy, the cells contained filopodia, abundant endoplasmic reticulum, and moderate numbers of low‐density membrane‐bound granules. This case documents a previously undescribed granular variant of a histiocytic tumor in a cat. [ABSTRACT FROM AUTHOR]

Xanthogranulomatous inflammation is a rare benign inflammatory lesion characterized by sheets of lipid-laden foamy histiocytes. It has been reported in various organs, mainly the kidney and gall bladder. Xanthogranulomatous endometritis (XGE) is sporadic, with only a few cases reported in the English medical literature. Herein, we report a case of xanthogranulomatous endometritis with the formation of stones in a 50-year-old female patient with a prolapsed uterus. Grossly the endometrium was irregular, and the uterine cavity was filled with a yellow friable material, a polypoid growth, and yellowish stones. The microscopy showed sheets of histiocytes with few preserved endometrial glands. In this case, the xanthogranulomatous inflammation may mimic a clear cell carcinoma involving the endometrium and myometrium. One of the important differential diagnoses is malakoplakia. Immunohistochemistry and special stains are helpful in diagnosis.

Xanthogranulomatous inflammation, a specific form of chronic inflammation, is marked by parenchymal destruction, proliferative fibrosis, and infiltration of typical foamy histiocytes admixed with hemosiderin-laden macrophages and foreign-body giant cells. Myometrial xanthomatosis, a term designated for nodular or diffuse histiocytic hyperplasia of the myometrium, has been reported in association with pregnancy-related procedures. Moreover, a 2–3-fold increase in histiocytic counts has been observed in leiomyomatous areas than in adjacent normal myometrium. The first evidence of collections of lipid-laden macrophages was documented in the form of yellowish degeneration of uterine leiomyomas. We report a case of xanthogranulomatous change in a leiomyoma in a 47-year-old female who presented with abnormal uterine bleeding. To the best of our knowledge, this is the first report of xanthogranulomatous variant/degenerative change in a leiomyoma. This case highlights a new variant of leiomyoma which both gynecologists and pathologists should be aware of as it may pose a diagnostic challenge both clinically as well as pathologically.

Background: Juvenile xanthogranuloma is an uncommon benign mass that frequently arises among children. Regardless of its juvenile onset, the occurrence among the adult population is usually between the second and third decades of life. Case Report: We would like to present a case of adult xanthogranuloma in a 30-year-old male and a brief literature review of its etiology, histopathology, and management. Conclusion: Juvenile xanthogranuloma is a benign disease that is common in childhood but rare in adults. The diagnosis is confirmed by histological studies. The lesion is generally self-limiting and regresses spontaneously; however, surgical excision can be performed for cosmetic or diagnostic purposes. [ABSTRACT FROM AUTHOR]

Juvenile Xanthogranuloma is a non-neoplastic skin lesion of the non-Langerhans histiocytosis type, which mainly affects the pediatric population and usually has a self-limited course. Exceptionally, the lesion is multifocal, ocular and even visceral, causing severe complications. We present the case of two 10-year-old female patients, with no other symptoms or important history, both with a single lesion, one on the thigh, with 3 months of evolution, the other on the scalp, with 4 months of evolution, both with progressive growth and surgically removed. The anatomopathological study identified multiple histiocytes in the dermis, with cytoplasmic lipidization and forming giant multinucleated cells, some of the Touton type, characteristic of this lesion. This unusual entity is reviewed, with emphasis on the histopathological criteria and the usual clinical course.

The classic variant consisted of Touton giant cells and vacuolated mononuclear cells, while the transitional variant consisted of non-Touton giant cells with admixed vacuolated mononuclear cells and spindled cells. Keywords: foam cells; histiocytes; juvenile xanthogranuloma; papular xanthoma; xanthomatosis EN foam cells histiocytes juvenile xanthogranuloma papular xanthoma xanthomatosis 1 7 7 01/02/23 20230101 NES 230101 Papular xanthoma is a rare clinical entity with 53 cases previously reported in the literature. Papular xanthoma and JXG were considered the histopathologic differential diagnosis, and papular xanthoma was ultimately favored given the histopathologic findings. [Extracted from the article]

Histiocytic Sarcoma (HS) is a rare malignant neoplasm characterised by the neoplastic proliferation of cells showing morphological and immunophenotypic features of mature histiocytes. Majority of the reported cases present in extranodal sites, such as the head and neck, thyroid, duodenum, small intestine, colon, urinary bladder, spleen, and leptomeninges. This report documents a case of primary involvement of the salivary gland by HS. A 77-year-old male patient presented with a firm swelling in the left submandibular region for the last three months. Multiple lymph nodes, along with the presence of lung and liver nodules, were seen. Thus the final diagnosis of HS was made based on histopathology and IHC. Palliative chemotherapy was given to the patient, responded well, and has been well for the last year. The present study is probably the first case of HS involving the submandibular gland. [ABSTRACT FROM AUTHOR]

Competing Interests: The authors declare no conflict of interest.

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