MSK for Monday, June 1st, 2026

History

A two-month-old boy was referred for a second opinion and ultrasound to evaluate a bluish subcutaneous mass on the right flank with initial clinical and ultrasonographic suspicion of a vascular lesion. Before scanning, we turned on the lights to have a closer look at the lesion. A painless blue-red nodular lesion was noted.  This nodule was very hard, not typical of an infantile hemangioma, which should prompt the radiologist to keep this in mind during ultrasound interpretation.

During the consultation with the dermatologist, the mother mentioned that an asymptomatic violaceous macula had been present since birth. Over time, a palpable subcutaneous lesion developed beneath it.  The child was otherwise healthy with normal growth and development. Dermatological examination revealed a subcutaneous mass adherent to the overlying skin but mobile over the deeper planes, with a very firm consistency, topped by a violaceous discoloration of the skin without any epidermal changes. No additional cutaneous abnormalities were observed, aside from a superficial infantile hemangioma on the right thigh.

The subsequent ultrasound demonstrated a well-circumscribed hypoechoic nodule of approximately 13 mm in the dermis without posterior enhancement. There was only limited peripheral vascularity and a small arterial vessel deep to the lesion.

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Question

What is the most likely diagnosis?

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Correct answer

Juvenile xanthogranuloma

Discussion

This case illustrates the diagnostic difficulty associated with congenital and subcutaneous forms of juvenile xanthogranuloma (JXG), particularly when the lesion does not exhibit the characteristic yellow-orange appearance typically seen in cutaneous presentations. Subcutaneous or deep JXG can deviate from the classical clinical appearance and present with erythema or blue discoloration, complicating the diagnosis [1].

Congenital onset is relatively uncommon, occurring in approximately 10% of patients, and displays a broad range of morphologies, many of which differ from classical acquired cutaneous forms, making diagnosis challenging [2,3].

Ultrasound is often the first imaging modality in infants with soft-tissue masses, but its findings in JXG are often nonspecific. Deep and extracutaneous JXG typically appear as well-circumscribed, solid, hypoechoic lesions, often with absent or minimal internal Doppler flow, an appearance that can overlap with fibrous lesions [4]. Larger radiologic series have demonstrated that radiologists rarely include JXG in the imaging differential diagnosis. In two independent cohorts, JXG was not mentioned as a differential consideration, highlighting the degree to which the imaging appearance is under-recognized and easily confused with other soft-tissue lesions [4,5].

Histopathological evaluation is essential in congenital or atypical presentations because clinical and radiologic differentiation remains unreliable. Multiple reviews emphasize the need for biopsy with immunohistochemistry when clinical or imaging findings diverge from classic JXG morphology [1,2,3]. JXG demonstrates diffuse CD68 positivity and negativity for CD1a and langerin. These features were present in our case and are consistent with previously documented congenital and subcutaneous JXG presentations [6].

The prognosis of solitary cutaneous or subcutaneous JXG is excellent. Studies demonstrate spontaneous regression within months to years, and even large congenital lesions typically diminish without intervention [3]. Systemic involvement is rare and usually associated with multiple cutaneous lesions; however, solitary lesions such as the one described in this case do not generally require systemic evaluation beyond clinical monitoring [2].

In conclusion, congenital juvenile xanthogranuloma may present as a subcutaneous mass and may be clinically and radiologically misdiagnosed as a vascular tumor. Radiologic diagnosis is challenging due to its nonspecific imaging features, which often differ from those expected in hemangiomas. Therefore, the radiologist can play an important role by carefully assessing the lesion, turning on the lights to look at the lesion, considering clinical history, growth pattern and imaging characteristics, and recognize when findings are atypical for vascular lesions to ensure further diagnostic steps. When imaging and clinical features are inconclusive and overlap with fibrous lesions, biopsy remains essential for establishing a definitive diagnosis. Increased awareness of this entity among radiologists may help prevent misclassification and ensure appropriate patient management.

Differential diagnosis

Infantile hemangioma
Initially suspected because of the congenital bluish-red discoloration and subcutaneous location. However, the lesion demonstrated marked firmness on palpation and only limited peripheral Doppler vascularity, which are atypical features for an infantile hemangioma.

Infantile myofibroma
May present as a congenital or early infantile firm subcutaneous mass with a well-circumscribed hypoechoic appearance on ultrasound and limited vascularity. Imaging overlap with JXG can make distinction difficult.

Dermoid/Epidermoid cyst
Can appear as a well-defined superficial mass in infants but is less likely in the absence of posterior acoustic enhancement or internal cystic features.

Congenital infantile fibrosarcoma
An important malignant consideration in congenital soft-tissue masses. Typically presents as a larger, more aggressive, and often hypervascular soft-tissue lesion than seen in this case.

References

• 1. Janney C.G., Hurt M.A., Santa Cruz D.J. Deep Juvenile Xanthogranuloma: Subcutaneous and Intramuscular Forms. Am J Surg Pathol. 1991; 15(2): 150-159. DOI: 10.1097/00000478-199102000-00008. 2. Cichewicz A., Bialecka A., Mecinska-Jundzill K., Adamska U., Bialecki M., Neska-Dlugosz I., Grzanka D. Congenital Multiple Juvenile Xanthogranuloma. Adv Dermatol Allergol. 2019; 36 (3): 365-368. DOI: 10.5114/ada.2019.85643. 3. Oza V.S., Stringer, T., Campbell C., Hinds B., Chamlin S.L., Frieden I.J., Shah S. Congenital-Type Juvenile Xanthogranuloma: Case Series and Literature Review. Pediatr Dermatol. 2018; 35: 582-587. DOI: 10.1111/pde.13544. 4. Ginat D.T., Vargas S.O., Silvera V.M., Volk M.S., Degar B.A., Robson C.D. Imaging Features of Juvenile Xanthogranuloma of the Pediatric Head and Neck. AJNR. 2016; 37: 910-16. DOI: 10.3174/ajnr.A4644. 5. Chen Y., Yang Z., Shi J., Qiao Z. Imaging Features of Juvenile Xanthogranuloma. Pediatr Radiol. 2023; 53: 265-272. DOI: 10.1007/s00247-022-05486-5. 6. Saifaldein A.A., Almahmoudi F.H., Babgi R.I., Alsammahi, A.A. A Subcutaneous Juvenile Xanthogranuloma in a 4-Year-Old Girl. Case Rep Ophthalmol. 2019; 10:153-159. DOI: 10.1159/000500224.