Purpose or Case Report: Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue neoplasm presenting as a mass in the subcutis or deep dermis in the extremities of children and young adults. Although previously regarded as ‘malignant’, due to its benign microscopic appearance and favorable prognosis, this tumor was categorized as an “intermediate tumor of uncertain differentiation” in the 2013 World Health Organization classification.

AFH is often misdiagnosed on imaging and pathology. We will present the unusual case of AFH with extensive lymphadenopathy and multiple episodes of anemia. The imaging findings will be illustrated with radiographic, ultrasound, MRI, and PET/CT exams. We will also present gross specimen and pathology images.

Our case involves a 9 year old male presenting with asymptomatic left upper arm and left chest wall masses for two years. A previous biopsy of the mass and a lymph node had been performed, showing juvenile capillary hemangioma and benign progressive germinal transformation, respectively. The patient had several prior episodes of anemia requiring multiple blood transfusions. Coagulopathy workup was negative, and it was postulated that bleeding into the mass could be the source of the anemia.

Radiographs revealed a 4.5 cm ovoid mass in the posteromedial soft tissues of the upper left arm with stable size but increasing calcific serpiginous opacifications throughout the lesion compared to two years prior. Multiple round soft tissue nodules within the left axillary region were also present.

MRI revealed a heterogeneous lesion with a calcified rim with significant susceptibility artifact likely from hemosiderin. Several enlarged adjacent lymph nodes were present with additional marked lymphadenopathy filling the left axilla abutting the brachial plexus and neurovascular bundles, extending superiorly above the acromion. The largest lymph node measured 2.8 cm within a cluster of lymphadenopathy measuring 9 x 4 x 4 cm, increased compared to MRI two years prior. PET/CT revealed increased radiotracer uptake in the mass with a max SUV of 4.5 and within the left axillary lymphadenopathy with a max SUV of 6.5.

The patient underwent surgical excision of the mass with dissection and removal of two adjacent palpable lymph nodes. The mass had a firm capsule with a red/myxoid appearance measuring 6.0 x 5.0 cm. Pathology of the mass was consistent with angiomatoid fibrous histiocytoma and pathology of the lymph nodes revealed reactive follicular hyperplasia.
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