Castlemans disease (CD) is a rare lymphoproliferative disorder first described in the 1950s by Benjamin Castleman (Pai et al., 2022).  It is classified into unicentric (UCD) and multicentric (MCD) types, with MCD often linked to systemic symptoms driven by interleukin-6 (IL-6) dysregulation. UCD generally appears as an isolated, enlarged lymph node, most frequently located in the mediastinum, neck, or abdomen (van Rhee et al., 2018; Akter et al., 2025). Histologically, the hyaline-vascular variant (HV-UCD) is defined by atrophic germinal centers, concentric mantle zone hyperplasia, and prominent vascular proliferation (FETICA et al., 2014). Our case involves an eight-year-old girl with an isolated supraclavicular mass, confirmed as HV-UCD on biopsy. Surgical excision remains the optimal treatment, yielding a 91% five-year survival rate (Van Rhee et al., 2020). Genetic analyses suggest MAPK pathway mutations in UCD, indicating possible shared pathogenic mechanisms with idiopathic MCD (Butzmann et al., 2021).

We report the case of an eight-year-old girl with no significant medical history who presented with a mobile swelling in the right supraclavicular region. Clinical examination revealed an isolated supraclavicular lymphadenopathy, with no hepatosplenomegaly or other signs of systemic involvement. A thoracoabdominopelvic computed tomography (CT) scan showed multiple infra-centimetric lymph nodes in both supradiaphragmatic and subdiaphragmatic regions, with no associated abnormalities.

An excisional lymph node biopsy was performed, revealing an oval-shaped mass measuring 2.5 × 2 × 1 cm, with a firm consistency, grayish appearance, and hemorrhagic foci. The entire specimen was embedded in four blocks for histopathological analysis. Microscopic examination showed significant alterations in the lymph node structure, characterized by atypical follicular hyperplasia. The involuted lymphoid follicles exhibited an "onion skin" pattern, due to the concentric arrangement of mantle zone cells. There was also hyperplasia of follicular dendritic cells, forming concentric layers, sometimes associated with marked hyalinization foci. The interfollicular zones were hyperplastic, with notable vascular proliferation, sometimes exuberant, contributing to increased capillary density. These structural modifications significantly disrupted the normal lymph node architecture, largely obliterating the sinuses (Fig. 1, 2 and 3).

Fig. 1: Follicular hyperplasia disrupting the normal architecture, with large reactive and atrophic follicles (x25).

An immunohistochemical study was performed on paraffin-embedded tissue, using a panel of antibodies, including CD20, CD3, CD21, and CD138. The results showed:

• CD20: Positive staining of lymphoid nodules and infiltrate.
• CD3: Immunostaining of small interfollicular lymphocytes.
• CD21: Highlighting of follicular dendritic cells.
• CD138: Presence of plasmacytic aggregates in the interfollicular areas.

Fig. 2: Lymphoid follicle displaying an "onion-skin" pattern with hyalinized capillaries (x100).

These findings, combined with the absence of extensive lymph node involvement, led to the diagnosis of idiopathic unicentric Castleman disease (UCD), hyaline-vascular type. Additional analyses ruled out infection with herpes simplex virus (HSV-1/HSV-2) and HIV. Initial corticosteroid therapy was administered, resulting in partial improvement of systemic symptoms. 

Unicentric Castleman disease (UCD) is a rare lymphoproliferative disorder first described in case reports from the 1950s (Pai et al., 2022). It is marked by localized lymph node enlargement and, while often asymptomatic, can manifest as an isolated lymph node mass, a presentation widely reported in the literature (Van Rhee et al., 2020). 

In our case, histopathological analysis revealed a pattern of atypical follicular hyperplasia, displaying concentric layering of mantle zone cells, forming the characteristic "onion-skin" appearance described in hyaline-vascular UCD (Du et al., 2025). This variant is also recognized for its pronounced follicular dendritic cell hyperplasia and increased vascular proliferation, both of which significantly disrupt normal lymph node architecture (van Rhee et al., 2018). Immunohistochemical findings further support the diagnosis, as CD20 positivity in lymphoid nodules and CD21 staining of follicular dendritic cells align with established diagnostic criteria for UCD (Van Rhee et al., 2020). Additionally, the CD138-positive interfollicular plasmacytic aggregates observed in our case have been consistently reported as characteristic features of UCD (FETICA et al., 2014). Furthermore, the absence of extensive lymph node involvement and the negative testing for HHV-8 and HIV effectively ruled out multicentric disease and viral etiologies, which are known to be associated with certain Castleman disease subtypes (Comité de rédaction de lOMS sur la classification des tumeurs, s. d.). From a therapeutic standpoint, current guidelines advocate for complete surgical resection as the treatment of choice for UCD, reporting a 5-year survival rate of 91% following successful excision (Van Rhee et al., 2020). Our patient exhibited an uneventful postoperative course with no signs of recurrence or complications, reinforcing previous findings that surgery is highly effective in achieving long-term remission (Butzmann et al., 2021). In cases where resection is not feasible due to anatomical constraints, radiotherapy has been proposed as an alternative approach, demonstrating a disease control rate of 82% at 20 months (Van Rhee et al., 2020). Recent advances in molecular pathology have revealed that somatic mutations, particularly PDGFRB N666S, are present in some UCD cases, suggesting a possible clonal neoplastic origin (Butzmann et al., 2021). Other reports have highlighted genetic alterations affecting CARD11, a key regulator of the NF-κB signaling pathway, which may contribute to the pathogenesis of the disease. Furthermore, shared MAPK pathway alterations between UCD and idiopathic multicentric Castle-man disease (iMCD) indicate possible overlapping pathogenic mechanisms (Butzmann et al., 2021).

While interleukin-6 (IL-6) is a well-established driver of multicentric Castleman disease, its role in UCD remains less defined. Nevertheless, some studies suggest that IL-6 may still contribute to systemic inflammatory symptoms observed in certain UCD cases (Du et al., 2025). This aligns with findings indicating that some patients with UCD exhibit elevated IL-6 levels and associated symptoms (Dispenzieri et al., 2012). Long-term follow-up remains essential for patients undergoing surgical treatment, even though recurrence rates remain low (Wong, 2018). Notably, some reports have linked UCD with an increased risk of malignancies, including follicular dendritic cell sarcoma and B-cell lymphomas, thereby emphasizing the importance of ongoing surveillance. Additionally, autoimmune complications, such as paraneoplastic pemphigus, have been documented in association with UCD, necessitating a multidisciplinary management approach (Wong, 2018).

Although siltuximab, an IL-6 monoclonal antibody, has shown significant efficacy in the treatment of idiopathic multicentric Castleman disease, its role in UCD is less clear due to the minimal involvement of IL-6 in this form of the disease (Dispenzieri et al., 2012). However, in cases where surgical resection is not possible or when severe inflammatory manifestations occur, the use of siltuximab may be considered as an adjunct therapy (van Rhee et al., 2018). In conclusion, our case highlights the characteristic clinical and histopathological features of hyaline-vascular UCD. The successful surgical management observed in our patient supports the current consensus that complete excision remains the primary curative approach (Van Rhee et al., 2020). Furthermore, ongoing research into the genetic underpinnings of UCD may lead to novel therapeutic strategies, particularly for unresectable or recurrent cases (Butzmann et al., 2021).

Our case provides valuable insight into the clinical and pathological features of unicentric Castleman disease (UCD) in pediatric patients. The present-ation of an isolated supraclavicular mass in an eight-year-old girl, confirmed as the hyaline-vascular variant through histopathology and immunohistochemistry, aligns with documented characteristics of the disease. Surgical excision, the gold standard treatment, led to a favorable outcome with complete remission and no recurrence to date. This case underscores the need for increased awareness of UCD in children and highlights the necessity of long-term follow-up to monitor potential complications.

A.E.H.M.: Study conception, pathological analysis, figure preparation, manuscript writing, and final approval. A.A.B.: Clinical data collection and patient follow-up. Z.E.E.: Manuscript review and final approval. S.M. S.M.M.L.: Clinical data collection and patient follow-up. M.A.D.: Manuscript review and final approval. C.S.A.T.: Manuscript review and final approval. M.M.Y.E.: Manuscript review and final approval. E.H.M.: Manuscript review and final approval.

The authors have acknowledged authority of the institutions and take full responsibility for all aspects of this work, ensuring that any questions regarding the accuracy or integrity of any part of the study are thoroughly investigated and addressed. 

The authors declare that they have no conflicts of interest, financial or otherwise, that could have influenced the conduct or outcomes of this study.