OBJECTIVE: Within the large umbrella of histiocytosis are a few similar yet heterogenous entities involving the orbit and periocular tissues with or without systemic infiltration, termed adult onset xanthogranuloma or orbital xanthogranuloma. Due to rarity of these conditions, different classifications in use, diverse clinical presentations and still unknown etiology, the aim of this paper was to provide an up-to-date literature review of the actual understanding of histiocytosis and its subgroups involving the orbit and periocular area, diagnostic strategies and therapeutic modalities.
METHODS: We present a review of literature and small case series comprising four patients diagnosed and treated in the period from 2001 until 2023 in our hospital. Clinical files of 4 patients with adult-onset xanthogranulomatous disease of the orbit and ocular adnexa (AOXGD) were reviewed retrospectively. Clinical, laboratory, radiological, histopathological, and immunohistochemical findings were reexamined.
RESULTS: Reviewing medical records of our patients with AOXGD, we found significant overlap between histiocytosis and different immune disorders. A broad workup should be considered in these patients as they can harbour severe immune disfunctions and hematologic disorders. Preferred treatment modality depends on a histopathologic type of AOXGD, clinical presentation and systemic involvement and should be conducted multidisciplinary.
CONCLUSIONS: The diagnosis is often delayed because of its rarity and diverse clinical findings. Development of molecular genetic tests, detection of BRAF V600E mutation and different types of kinase mutations, mutations in transcriptional regulatory genes as well as tyrosine kinase receptors have shed a new light on the etiopathogenesis and potential targeted treatment of histiocytosis.

Rosai-Dorfman disease (RDD) is an uncommon histiocytic disorder that occurs in nodal and/or extranodal sites. Extranodal RDD exhibits a wide range of clinical and radiological presentations, frequently leading to misdiagnoses. Involvement of the gastrointestinal (GI) system is uncommon, accounting for less than 1% of the reported cases. Here we present a case of a 54-year-old male who complained of abdominal distention and was diagnosed with RDD affecting the sigmoid colon, manifesting as a sigmoid mass. The patient had a past medical history of liver transplantation due to hepatocellular carcinoma (HC). This report details the multiphase contrast-enhanced computed tomography (CT) and fluorodeoxyglucose (18F-FDG) positron emission tomography (PET-CT) imaging findings of RDD involving the sigmoid colon without lymphadenopathy, and a review of the relevant literature is provided.

UNASSIGNED: We report a patient who initially visited the ophthalmology clinic for a vision loss diagnosed with Erdheim-Chester Disease (ECD).
UNASSIGNED: ECD is a rare non-Langerhans cell histiocytosis characterized by multisystemic organ involvement and poor prognosis. Our patient had complete vision loss due to prominent orbital involvement before any systemic symptoms appeared. This case demonstrates variable clinical manifestations of ECD.
UNASSIGNED: Painless bilateral proptosis with poor response to steroid treatment should prompt consideration for ECD and systemic evaluation. In addition, in the absence of typical clinical manifestations, a thorough evaluation of the biopsy can be crucial for an accurate diagnosis.

Langerhans Cell Histiocytosis (LCH) is a typically benign disorder that affects infants predominately, with adult occurrence being uncommon. We discuss the case of a 22-year-old guy who visited our clinic complaining of three months of acute nape pain and upper limb radiculopathy. Notably, the patient had no history of trauma, fall injuries, or tuberculosis. Radiological tests identified a single osteolytic lesion within the C3 vertebral body. The lesion was removed, an anterior C3 corpectomy and discectomy were performed, and the patient\'s spine was reconstructed with a titanium cage and plating. The patient\'s nape discomfort and radiculopathy vanished almost instantly after surgery. A definitive diagnosis of LCH was confirmed through histological examination. This case report illustrates the unusual and uncommon occurrence of LCH at the C3 vertebral body, for which fusion surgery was the only viable therapeutic option. The patient\'s recovery from radiating pain following the surgical procedure demonstrates the effectiveness of the intervention. LCH in the cervical spine is rather rare, but it is nevertheless important to be aware of the possibility of developing it.

BACKGROUND H syndrome is an autosomal recessive disorder of histiocytic proliferation with clinical spectrum of unique cutaneous and systemic manifestations. There is no consistent treatment for the disease, and all available options are based on case reports. Here, we present the chronological progression of a case of H syndrome with typical cutaneous manifestations that was misdiagnosed early as meningitis-induced sensorineural hearing loss and later as a non-defined autoimmune connective tissue disease. A new tried, although failed, treatment option is described as well. CASE REPORT A 31-year-old Saudi woman born of a consanguineous marriage presented to our dermatology clinic with symmetrical indurated hyperpigmented to violaceous plaques over the medial thighs, upper legs, lower back, volar wrists, and upper arms, associated with hypertrichosis. Hallux valgus of the big toes was clinically detected as well. She had a history of sensorineural deafness, diabetes mellitus, chronic anemia, and hypothyroidism. Genetic analysis of the patient showed a homozygous frameshift pathogenic variant of the SLC29A3 gene, c.243del p.(Lys81Asnfs*20). Systemic treatments in the form of methotrexate and imatinib had been tried; however, both failed to control her sclerotic cutaneous changes. CONCLUSIONS Knowing the early life presentation and the variable clinical symptoms of H syndrome is crucial in early intervention and further prevention of the non-reversible changes. Moreover, avoiding unnecessary immunosuppressive medication use is warranted in certain circumstances.

Eosinophilic granuloma (EG), a subtype of Langerhans cell histiocytosis (LCH), the monostotic form, is a rare condition characterized by a solitary bone lesion. It is even more unusual for this condition to be accompanied by an epidural hematoma (EDH). This case is unique in that it is the first to involve delayed EDH following a seizure. We describe a remarkable example of EG accompanied by an EDH and consider the rarity of this comorbidity. A 32-month-old boy developed a rapidly growing skull mass following a minor head injury. During surgical preparation for a biopsy, the patient experienced a single convulsion. Imaging following the seizure revealed an EDH in the vicinity of the mass. The mass was excised and confirmed to be an EG, but with positive margins. The patient underwent chemotherapy after systemic skeletal evaluation, in accordance with the LCH III protocol established by the Histiocytosis Society. EG is a rare neoplasm that typically presents as a painless growth on the skull that gradually enlarges over time. The correlation between EG and EDH is exceedingly uncommon, with only a few documented cases. This case study underscores the significance of considering EG in the differential diagnosis of an expanding cranium mass, even when associated with EDH. Prompt diagnosis and treatment can prevent serious complications and improve patient outcomes.

报道多系统受累的间变性淋巴瘤激酶（ALK）阳性组织细胞增生症1例。患者女，35岁。因发现左乳肿物10 d入院。镜下见乳腺组织内梭形细胞增生、交错排列，细胞核卵圆形，核分裂象罕见，胞质丰富、嗜碱或透亮，背景可见散在淋巴细胞浸润，及散在残存的脂肪细胞及乳腺导管。免疫组织化学染色显示异常增生的梭形细胞CD68、CD163、ALK阳性，广谱细胞角蛋白（CKpan）、p63、Langerin、S-100蛋白、CD34、β-catenin、结蛋白、Calponin、STAT6阴性。ALK荧光原位杂交（FISH）分离探针检测显示ALK基因有断裂。二代测序于DNA及RNA水平均检测到ALK：：KIF5B基因融合。ALK阳性组织细胞增生症是新近收录于第5版WHO造血与淋巴组织肿瘤的罕见病例，是伴有ALK：：KIF5B基因融合的独特亚型，常常伴有多系统受累，ALK抑制剂靶向治疗有效、但远期生存情况不明确。经验不足的医师容易因认识不足而误诊，因此需要充分认识其临床表现、病理特征与分子改变。.

Erdheim-Chester Disease (ECD) is a rare form of histiocytosis characterized by xanthomatous infiltration of affected organs. We present a case of a 62-year-old man with ECD initially presenting with constrictive pericarditis. Comprehensive imaging revealed systemic involvement, including the skeleton, orbit, pituitary, lung, kidney, and retroperitoneum, despite the absence of related symptoms. The diagnosis of ECD was eventually confirmed through histopathological evidence from a CT-guided biopsy. The patient responded well to interferon-α2b treatment, with gradual symptom amelioration and improvement in imaging and laboratory findings over a 5-month follow-up period. This case highlights the importance of considering ECD in the differential diagnosis of constrictive pericarditis and the utility of multimodal imaging for accurate diagnosis and management of this rare disease. The patient\'s positive response to treatment also highlights the potential for effective management of ECD, particularly with early diagnosis and intervention.

Langerhans cell histiocytosis (LCH) is a rare disease with limited treatment options. We present a case involving a 57-year-old woman afflicted with an isolated LCH bone osteolytic lesion. A single bisphosphonate infusion significantly alleviated pain, and follow-up scans via CT, PET-CT, and MRI revealed a substantial recalcification of the lesion. Conducting an extensive literature review, we identified 46 cases documenting the efficacy of bisphosphonates in the context of LCH. These findings have raised interest in bisphosphonate infusion as a simple therapeutic alternative in similar situations, with benefits in terms of bone recalcification and pain control for individuals with LCH.

Crystal-storing histiocytosis (CSH) is a rare condition in which crystals accumulate in the cytoplasm of histiocytes and is usually associated with a lymphoplasmacytic neoplasm. Cutaneous CSH is extraordinarily rare and limited to case reports in the literature. We report two cases of this disease with cutaneous involvement. Case 1 was a 65-year-old male with a 4-month history of a pruritic eruption that started as a solitary pink to skin-colored indurated plaque on the anterior neck before progressing to involve the whole neck, chest wall, and face. Case 2 was a 54-year-old woman with a history of unspecified \"lymphoma\" who presented with a soft nodule on the forearm. Biopsies from both cases had similar findings and showed a proliferation of epithelioid cells with pink cytoplasm and intracellular crystalline structures infiltrating the dermis and subcutaneous fat. In the first case, the cells were positive for CD43, CD45, CD68, and IgG kappa, and in the second case, the crystals were positive for IgG lambda. Based on these findings, the patients were diagnosed with cutaneous CSH. We highlight this rare diagnosis and the importance of investigating an underlying lymphoplasmacytic neoplasm.