Pulmonary artery angiomatoid fibrous histiocytoma mimicking pulmonary embolism

Background

Angiomatoid fibrous histiocytoma (AFH) is a rare soft tissue neoplasm of intermediate biological potential that commonly arises in the superficial soft tissue of the extremities of children and young adults.1 AFH occurring in the pulmonary parenchyma is a rare tumour with about 14 cases reported in literature.2 Intraluminal pulmonary artery AFH is even more rare with only three previously reported cases in the English-language literature.3–5

We document the fourth case of intraluminal pulmonary artery AFH reported in the English-language literature.

Case presentation

A man in his 20s presented to the emergency department (ED) with acute-onset pleuritic chest pain and shortness of breath. He recently had a long 9-hour flight. He had received his coronavirus vaccine 2 weeks prior to presentation. He had never smoked and had no medical history. Upon arrival to the ED, he was afebrile with a heart rate of 83 beats/min, blood pressure of 143/82 mm Hg, oxygen saturation of 99% and respiratory rate of 18. Physical examination did not reveal any abnormality.

Investigations

Bloodwork revealed normal basic metabolic panel with a creatinine of 1.13 mg/dL (normal: 0.7–1.30), normal brain natriuretic peptide, haemoglobin of 116 g/L (normal: 130–170 g/L), thrombocytosis with platelet count of 421x10⁹/L (normal: 140 –400) and elevated D-dimer 0.54 mg/L FEU-Fibrinogen Equivalent Unit (normal <0.49). ECG demonstrated an isolated ST-segment elevation in lead V3. Given his presentation, risk factors and elevated D-dimer, CT angiography (CTA) was done. The preliminary report revealed a lobulated filling defect in the left main pulmonary artery consistent with pulmonary embolism (PE). However, the final report of the CTA described a 3.4 cm mediastinal mass compressing on the pulmonary artery and resulting in a 95% narrowing of the artery lumen (figure 1). A transthoracic echo revealed normal right and left ventricular function and the presence of a mass abutting the left atrium.

Figure 1

CT angiography showing filling defect in the pulmonary artery.

MRI of the chest showed a heterogeneously enhancing, partially necrotic 3.3 cm soft tissue mass located mostly inside the left pulmonary artery and extending into the mediastinum anterior to the left mainstem bronchus (figure 2).

Figure 2

MRI of the chest with contrast showing a large necrotic mass in the pulmonary artery.

Differential diagnosis

For any patient who presents with shortness of breath, pleuritic chest pain, recent long-distance travel and positive D-dimer, PE is on top of the differential, as was for our patient. Pulmonary artery intraluminal tumours can easily be misdiagnosed as PE, only to be diagnosed during thrombectomy or at autopsy. Intraluminal tumours include pulmonary artery sarcomas, primary myxoid pulmonary tumours or rarely AFH or lung cancer, intra-arterial extension or even with external compression of the pulmonary artery. Diagnosis for the intraluminal tumour would be based on histology, immunohistochemical profiling, and, if needed, molecular evaluation as in our case.

Outcome and follow-up

A pulmonary artery sarcoma was the main consideration on the needle core biopsy based on the intra-arterial location and the presence of atypical cells suspended in a myxoid stroma. The resection specimen demonstrated an intraluminal mass within the dilated lumen of the pulmonary artery (figure 3). Microscopically, the tumour consisted of cellular nodules of plump spindled and epithelioid histiocyte-like cells with mildly atypical oval and retiform nuclei, lightly eosinophilic cytoplasm and ill-defined cytoplasmic borders within a partially myxoid and haemorrhagic stroma (figure 4). Mitotic activity peaked at 4 mitoses in 50 high-powered fields and the Ki-67 proliferative index was approximately 5% (low). Small foci of tumorous necrosis were observed. Notably, the process was well marginated and partially surrounded by a fibrous pseudocapsule and a brisk lymphoplasmacytic infiltrate (figure 5). Immunohistochemically, the tumour cells variably expressed CD99 and ALK-1, focally expressed CD68 and CD34, and exhibited very focal expression of desmin. Tumour cells were negative for smooth muscle actin, EMA, S100 protein and D2-40. EWSR1 gene rearrangement was detected by ‘break-apart’ FISH(Fluorescence In Situ Hybridization). SYT gene rearrangement and MDM2 amplification were not detected by FISH. The characteristic histological findings coupled with the immunoprofile and molecular results confirmed the diagnosis of an AFH arising within the pulmonary artery.

Figure 3

Cut surface of tumour within the pulmonary artery. The tumour is bivalved to reveal a cavity filled with haemorrhagic material. The remainder of the tumour is homogeneous soft and tan-yellow in colour.

Figure 4

H&E, 200×. Nodules display ovoid and spindled tumour cells with myxoid stroma, mild atypia and very low mitotic index.

Figure 5

H&E, 40×. Low-power magnification showing dense fibrous pseudocapsule and nodules of tumour cells with lymphoplasmacytic cuffing.

He subsequently underwent staging CT of the abdomen and pelvis, which did not show any evidence of metastatic disease. The patient remained stable throughout with complete resolution of symptoms. He was discharged with outpatient follow-up with cardiothoracic surgery and oncology and has not experienced a recurrence during a 12-month follow-up interval.