Rare localization of a rhabdoid tumor in the elbow of a 6-year-old child: A case report

Abstract

We report a rare case of a rhabdoid tumor of the elbow in a 6-year-old child. Rhabdoid tumors are aggressive and rare neoplasms, usually found in the kidneys or soft tissues, and their occurrence in the elbow is exceptional, potentially delaying diagnosis. Imaging plays a key role in the evaluation, allowing assessment of tumor extent and its relationship with surrounding structures. In our patient, it revealed a solid, infiltrative mass in the distal third of the long head of the left biceps, with lobulated contours and intermediate T2 signal, showing moderate and heterogeneous enhancement after gadolinium, with infiltration of adjacent soft tissues, suggestive of a malignant lesion. Imaging is essential not only for initial tumor assessment but also for monitoring treatment response and identifying complications, as illustrated in our patient, in whom ultrasound revealed cervical lymph node involvement. Histopathological examination is essential for confirming the diagnosis, as rhabdoid tumors exhibit distinctive cellular features that can distinguish them from other neoplasms.

Introduction

Rhabdoid tumors are highly aggressive malignant tumors, first described by Beckwith and Palmer in the kidney, with rhabdomyosarcomatous features and aggressive behavior [1]. Rhabdoid tumors account for 0.26% of soft tissue sarcomas in patients ranging from 2 months to 56 years old, with the majority of cases occurring in children. The median age at diagnosis is 7.3 years, and the gender ratio is approximately 1:1.

It is currently referred to as TMR when located in the kidneys, atypical teratoid/rhabdoid tumor (TA/RT) in the brain and extracranial extrarenal rhabdoid tumor (TEER) in other body sites such as soft tissue or liver [2].

Data from the EU-RHAB registry, which prospectively collects clinical characteristics of rhabdoid tumors across Europe, show that among 100 patients with rhabdoid tumors, 70% were extracranial, extrarenal (eMRT) and 30% were renal rhabdoid tumors (RTK), indicating that extrarenal involvement constitutes the majority of non-CNS presentations in some cohorts [3].

This case study highlights an exceptional presentation of a rhabdoid tumor in the elbow of a 6-year-old child. This case aims to contribute to the limited literature on atypical rhabdoid tumor presentations, emphasizing the importance of considering a broad differential diagnosis in cases of pediatric tumors with unusual localizations. By documenting this rare instance, we hope to enhance clinical awareness and guide future research on the management of rhabdoid tumors in less commonly affected areas.

Case report

This 6-year-old girl, with no previous medical history and good psychomotor development, was admitted for a compressive axillary mass of the left upper limb, which had been evolving for 2 and a half months, causing paresthesia of the left upper limb with no other associated signs.

An ultrasound of the left axillary fossa, performed at another institution, revealed the presence of nonsuppurative left axillary lymphadenopathy. A lymph node biopsy was subsequently performed, which concluded in a reactive hyperplastic lymphadenitis.

Subsequently, the patient developed a progressive swelling of the left upper limb, associated with pain, which prompted her hospitalization. This clinical evolution occurred in a context of apyrexia, but with a deterioration in general condition, including a weight loss of 1.9 kg over 2 months. The initial laboratory workup showed: complete blood count with hemoglobin 10.9 g/dL, mean corpuscular volume (MCV) 68 fL, mean corpuscular hemoglobin (MCH) 26 pg, white blood cell count 5900/mm³ with neutrophils 3900/mm³, lymphocytes 1800/mm³, monocytes 200/mm³, and platelet count 229,000/mm³. C-reactive protein was <6 mg/L.

An initial ultrasound of the left arm revealed a large soft tissue mass on the anterior aspect of the left arm, ovoid in shape, poorly defined, and heterogeneously echogenic, measuring 47 × 27 mm, with infiltration of adjacent soft tissues (Fig. 1).

Fig. 1.

Ultrasound image showing a large soft tissue mass on the anterior aspect of the left arm, oval-shaped, poorly defined, with heterogeneous echogenicity, measuring 47 × 27 mm, infiltrating the surrounding soft tissues.

A complementary MRI of the left arm was then performed, demonstrating the presence of a solid mass, with intermediate signal on T2-weighted sequences, with lobulated contours, located in the distal third of the long head of the left biceps muscle, measuring 45 × 36 × 31 mm. The lesion showed moderate and heterogeneous enhancement following gadolinium administration, and was associated with infiltration of surrounding soft tissues (Fig. 2).

Fig. 2.

Sagittal, coronal and axial slices of an MRI of the left arm: (A) Sagittal T2 fat-saturated sequence, (B) Sagittal T1 nonfat-saturated sequence, (C) Coronal T1 nonfat-saturated sequence and (D) AxialT1 fat-saturated sequence. Presence of a solid mass (Orange star) with intermediate signal on T1 and T2, located in the left arm, with lobulated contours, situated in the distal third of the long head of the left biceps muscle. It infiltrates the adjacent tissues and is in close contact with the left humeral artery and vein.

A surgical excision of the mass was subsequently performed (Fig. 3). Under general anesthesia, a left anterolateral arm incision was performed, allowing for en bloc resection of the tumor mass, with the exception of a tumoral collar at the elbow crease in close proximity to the brachial pedicle, which was left in place in accordance with the preoperative strategy (nononcologic resection followed by radiotherapy). The ulnar, median, and musculocutaneous nerves were identified and preserved. The biceps muscle was retracted, and the brachial pedicle was respected. The procedure included copious irrigation, muscle repair, and tension-free closure with placement of a drain. The necrotic and friable specimen was sent for histopathological analysis. Histological examination, supplemented by immunohistochemical analysis, revealed features suggestive of a SMARCB1-negative rhabdoid tumor (Fig. 4). Microscopic examination showed a high-grade malignant tumor composed of confluent nodules and solid sheets, with focal alveolar-like areas, marked cellular pleomorphism, frequent vascular invasion, and ischemic necrosis involving less than 20% of the tumor area. Tumor cells exhibited rhabdoid morphology with eccentric nuclei, prominent nucleoli, and abundant eosinophilic cytoplasm, associated with a high mitotic rate (21/10 HPF). Infiltration of the adjacent fibro-adipose tissue with partial effacement of lymph node architecture was observed. Immunohistochemically, tumor cells showed strong and diffuse expression of pancytokeratin (AE1/AE3) and epithelial membrane antigen (EMA), with loss of INI1 expression, while markers of myogenic, neural, hematolymphoid, and neuroendocrine differentiation were negative, supporting the diagnosis of an INI1-deficient malignant rhabdoid tumor. Considering these findings, the final diagnosis of a SMARCB1/INI1-deficient extrarenal malignant rhabdoid tumor was established.

Fig. 3.

Operative image showing the tumor mass of the left arm (White arrow), The mass appeared vaguely nodular, with a reddish-blue hue, and contained focal yellowish areas consistent with fatty tissue.

Fig. 4.

The histopathological sections from our case: morphological features observed under light microscopy following hematoxylin and eosin (H&E) staining: (A) Sheets of cells infiltrating the hypodermis and dermis (H&E stain; 10 × 10 magnification), (B) Proliferation of cells with vesicular nuclei, prominent nucleoli, and abundant cytoplasm containing eosinophilic hyaline globules (H&E stain; 40 × 10 magnification) and (C) Proliferation of cells with atypical, irregular, and hyperchromatic nuclei (H&E stain; 20 × 10 magnification).

Based on these results, the patient underwent radiotherapy and chemotherapy according to the EpSSG protocol, which included an alternation of 9 VDCy and IE chemotherapy cycles (Vincristine–Cyclophosphamide–Epirubicin / Ifosfamide with Mesna–Etoposide), administered from October 2023 to February 2024. The treatment was complicated by 2 episodes of febrile neutropenia requiring hospitalization (after the 1st and 3rd cycles), one of which was associated with a left gluteal abscess, with good response to antibiotic therapy. The remaining cycles were overall well tolerated.

Unfortunately, the clinical course was marked by disease progression, with tumor escape and extension into adjacent soft tissues, including histologically confirmed axillary and left lateral cervical lymph node metastases (Fig. 5), occurring around the fourth month of chemotherapy.

Fig. 5.

Ultrasound image showing an axillary lymphadenopathy that developed 4 months after chemotherapy, The lesion exhibited a heterogeneous appearance, with purely anechoic areas suggestive of necrosis, measuring 25 × 11 mm.

Following a multidisciplinary team discussion, it was decided to discontinue curative-intent treatment and to initiate 4 to 5 sessions of palliative and analgesic radiotherapy.

Discussion

In this case report of an extrarenal rhabdoid tumor (ERRT) presenting in the elbow, it is important to relate our findings to previously published case reports and case series of ERRTs in atypical soft tissue locations. Although ERRTs most commonly occur in young children and in deep axial soft tissues (eg, neck, paraspinal region), there are scattered reports of these tumors in unusual extrarenal sites. For example, an ERRT arising within the sacral canal mimicked a peripheral nerve sheath tumor, underscoring the potential for diagnostic confusion in atypical locations [4]. Similarly, a case of ERRT infiltrating the brachial plexus and spinal canal in a young adult demonstrated rapid local progression and early recurrence despite aggressive therapy [5]. Other unusual extrarenal presentations include tumors of the heel and soft tissues of the pelvis, further illustrating the broad anatomic distribution of these neoplasms [6]. These reports help contextualize our case and raise awareness of ERRTs in locations where they are rarely considered.

Given the clinical and histologic overlap with other small round blue cell tumors and high-grade soft tissue sarcomas, a comprehensive discussion of the main differential diagnoses is warranted. ERRTs are composed of cells with abundant eosinophilic cytoplasm, prominent nucleoli, and often show loss of nuclear SMARCB1/INI1 expression, which is a critical diagnostic marker. The histologic features of ERRT may overlap with those of synovial sarcoma, Ewing sarcoma/PNET, rhabdomyosarcoma, lymphoma, and other SMARCB1-deficient tumors, making detailed immunohistochemistry essential for accurate classification [7]. The absence of SMARCB1/INI1 favors a diagnosis of rhabdoid tumor over many mimics, but other markers (eg, cytokeratins, vimentin, CD99, neural markers) must be interpreted in context to exclude alternate entities.

In addition to morphological considerations, molecular studies play an increasingly important role in differential diagnosis. For example, EWSR1 rearrangements are characteristic of Ewing sarcoma, and SS18-SSX fusions define synovial sarcoma (Fig. 6); neither is present in rhabdoid tumors. These molecular distinctions are critical, particularly in unusual locations where radiologic and morphologic features alone may be nondiagnostic [8].

Fig. 6.

Summary of major differential diagnoses of rhabdoid tumors with their characteristic histological appearances, immunohistochemical profiles, and key genetic features [10].

Our patient’s clinical course—marked by disease progression at approximately 4 months following initiation of chemotherapy, with extension into adjacent soft tissues and confirmed axillary and left lateral cervical lymph node metastases—is consistent with the historically poor prognosis of ERRTs. These tumors are highly aggressive, often progressing rapidly despite multimodal therapy. Previous literature notes that many ERRT patients succumb within a relatively short time after diagnosis, particularly when metastases or local invasion are present [9]. The development of regional lymphadenopathy and invasive extension in our case likely reflects an inherently poor prognostic trajectory and may explain the suboptimal response to chemotherapy.

The prognosis for Epithelioid Rhabdoid Tumors (ERRTs) is very poor, with low survival rates. Our patient’s clinical course—marked by disease progression at approximately 4 months following initiation of chemotherapy, with extension into adjacent soft tissues and confirmed axillary and left lateral cervical lymph node metastases—is consistent with the historically poor prognosis of ERRTs. These tumors are highly aggressive, often progressing rapidly despite multimodal therapy. Previous literature notes that many ERRT patients succumb within a relatively short time after diagnosis, particularly when metastases or local invasion are present [9]. The development of regional lymphadenopathy and invasive extension in our case likely reflects an inherently poor prognostic trajectory and may explain the suboptimal response to chemotherapy.

Conclusion

The presentation of a rhabdoid tumor in the elbow of a 6-year-old child is exceptionally rare and underscores the need for clinicians to consider a broad differential diagnosis when encountering pediatric tumors in uncommon locations.

This case highlights the importance of early and accurate diagnosis, as well as the need for a tailored treatment approach to address the unique challenges posed by atypical tumor locations. Further research and documentation of similar cases are essential to improve our understanding and management of rhabdoid tumors in less commonly affected areas.

Patient consent

Written informed consent was obtained from the patient’s legal guardians for the publication of this case report.