Rishabh Agrawal^*, Diego A L Garcia

University of Florida, Department of Radiology, Gainesville, FL, USA

^*Corresponding Author: Rishabh Agrawal, University of Florida, Department of Radiology, Gainesville, FL, USA

Received: 04 March 2026; Accepted: 10 March 2026; Published: 18 March 2026

Article Information

Citation: Rishabh Agrawal, Diego A L Garcia. Hemorrhagic Intramuscular Schwannoma Mimicking Myxoid Neoplasm in the Anterior Deltoid of a Patient with Cholangiocarcinoma: A Case Report. Journal of Radiology and Clinical Imaging. 9 (2026): 22-24.

DOI: 10.26502/jrci.2809126

Abstract

Keywords

Deltoid; Hemorrhagic degeneration; MRI; Oncology; Peripheral nerve sheath tumors; Schwannoma

Article Details

1. Introduction

Schwannomas are typically benign, encapsulated soft tissue masses with predictable MRI signals, such as T1 isointensity and T2 hyperintensity. However, degenerative changes—including cystic/myxoid degeneration and intralesional hemorrhage—can mask classic diagnostic signs like the "target sign" or "split-fat sign." In the context of a patient with known malignancy, such as cholangiocarcinoma, a new soft tissue mass frequently raises concern for rare skeletal muscle metastasis or treatment-related changes. This case highlights the role of MRI in distinguishing between necrotic metastases, myxoid sarcomas, and benign but atypical schwannomas.

2. Case Presentation & Imaging Findings

A 58-year-old female presented with a painful, enlarging mass in the anterior right shoulder. Physical examination revealed a firm, mobile, and tender mass without neurologic deficits.

MRI Evaluation:

• • Location and Morphology: A well-defined, lobulated 5.1 cm mass was centered within the anterior deltoid
• • Signal and Enhancement: The lesion was isointense on T1 and heterogeneously hyperintense on T2/STIR (Figure 1). Post-contrast sequences demonstrated thick peripheral enhancement with a non-enhancing central component, suggesting cystic or hemorrhagic degeneration (Figure 2).
• • Vascular/Neural Features: Tubular low-signal structures were noted along the margins, likely representing intratumoral vessels. A thin rim of fat (the "fat-cap sign") suggested encapsulation within the muscle (Figure 1).
• • Advanced Imaging: PET/CT showed intense peripheral FDG uptake (SUVmax of 5.20), mirroring the enhancement pattern seen on MRI and further complicating the exclusion of malignancy (Figure 3).

Figure 1: Sagittal T1-weighted (top left), Coronal T2-weighted fat-suppressed (top right), Axial T1-weighted (bottom left), Axial PD-weighted fat-suppressed (bottom right) demonstrate a well-defined intramuscular lesion surrounded by a thin, circumferential fat rim (“fat cap” sign). Note: The fat-cap sign suggests encapsulation but requires correlation to exclude low-grade malignancy

Figure 2: Coronal (left) and Axial (right) T1-weighted fat-suppressed post-contrast images demonstrate a well-circumscribed intramuscular centrally T1 hypointense with thick, irregular peripheral enhancement.

Figure 3: Coronal (top) and axial (bottom) PET/CT images demonstrate peripheral FDG uptake corresponding to the enhancing rim of the lesion, with no central metabolic activity.

3. Histopathology & Discussion

Ultrasound-guided biopsy revealed spindle cell proliferation with alternating Antoni A (hypercellular) and Antoni B (myxoid) areas. Presence of S100 protein positivity and hemosiderin-laden macrophages confirmed a schwannoma with recent hemorrhage. No epithelial malignancy was found, ruling out metastatic cholangiocarcinoma.

4. Differential Diagnosis:

Schwannomas demonstrate variable MRI characteristics depending on their internal composition. In this case, the peripheral enhancement pattern reflects the viable cellular component surrounding a hemorrhagic core.

It is important to emphasize that the "fat-cap sign" (or split-fat sign)—while a classic indicator of a peripheral nerve sheath tumor—is not strictly pathognomonic for benignity. While it suggests a slow-growing, encapsulated lesion that displaces rather than infiltrates adjacent fat, certain low-grade malignancies or even metastases with expansive growth patterns can occasionally mimic this appearance.

1. Intramuscular Myxoma: Often shows central T2 hyperintensity and peripheral enhancement but typically lacks the internal vascular/tubular structures seen in this case.
2. Soft Tissue Metastasis: While rare for cholangiocarcinoma, these are usually more infiltrative and lack a well-defined fat plane.
3. Myxoid Sarcoma: Usually presents with more aggressive features, such as ill-defined margins and extensive perilesional edema.

5. Conclusion

This case demonstrates that peripheral enhancement in an intramuscular lesion is not pathognomonic for myxoid neoplasms or necrotic metastases. While the "fat-cap sign" is a useful diagnostic clue, it must be interpreted with caution in oncologic patients as it does not definitively exclude low-grade malignancy. Schwannomas with hemorrhagic degeneration should remain a key consideration in the differential diagnosis of well-circumscribed intramuscular masses.

References

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