Sinonasal polyps are morphologically classified into five types – edematous, fibrous, glandular, cystic and angiectatic.1 Angiectatic Nasal Polyp (ANP), also known as angiomatous polyps, is a very rare type of sinonasal polyps. Angiectatic Nasal Polyp with Pleomorphism (PANP) are benign lesions of nose and paranasal sinuses,2 characterized by hemorrhage and necrosis, occasionally accompanied by bizarre large pleomorphic spindle cells hyperplasia. Clinically, it grows rapidly and exhibits an aggressive clinical behavior, simulating malignancy.3–6 In spite of its characteristic findings on imaging, however, it is radiologically challenging to pick it up. Therefore, histopathology features are essential for making definitive diagnosis.

In this report, we identified and summarized the features of thirteen patients with PANP from clinical manifestations, imaging, and histopathology. Awareness of these features would be helpful to avoid misdiagnosis and unnecessary treatment.

Angiectatic Nasal Polyp (ANP), a rare inflammatory sinonasal polyp, often develops secondary to changes in choanal polyp. It is vulnerable to vascular compromise in specific sites, such as ostium, posterior end of the inferior turbinate, choana and nasopharynx.2,7,8 Nasal obstruction is the most common symptom, followed by decrease or loss of smell perception, epistaxis, proptosis and visual disturbances.2,7–9

PANP is an exceedingly rare subtype of ANP. The course of the disease is long, the progress is slow, and the bone is swelling rather than erosive destruction. It is often unilateral, manifested as runny blood or epistaxis and accompanied by swelling destruction of the bone wall of the paranasal sinuses. Histologically, it is characterized by extensive vascular proliferation and dilation with Congo red negative pseudoamyloid material deposition.7 Shobha et al. found racemose aggregates of irregularly shaped blood vessels resembling dilated capillaries without elastic or muscular layers, accompanied by patchy necrosis and atypical stromal spindle cells.3,10,11 Electron microscopy and immunohistochemistry (CD34, factor VIII) results show endothelial cells lining the spaces and myofibroblasts in interstitium.2 On the MRI scan, T2-weighted images show internal heterogeneous hyperintensity with a peripheral hypointense rim while postcontrast images display a strong nodular and patchy enhancement.12,13 Vessel-like marked and progressive enhancement are important features on 2-phase helical CT scan. It is often associated with a soft tissue mass shadow of uneven density, with stripped and nodular high-density shadow located around and inside the lesion. The adjacent bone, especially the inner wall of maxillary sinus, shows discontinuous compression and absorption changes.

Given the manifestations of imaging and pathology, the diagnosis of PANP is still difficult because of potential confusion with Pleomorphic Hyalinizing Angiectatic Tumor (PHAT). PHAT is one of the low-grade intermediate ‒ locally aggressive soft tissue mesenchymal tumors with undetermined tissue differentiation.14 It mainly occurs in adults and is classified as undetermined differentiation tumors in soft tissue and bone tumors by WHO in 2020.15 Smith et al. first described its morphology, which is characterized by the expanded hyaline degeneration of the cluster thin-walled vessels, and pleomorphic spindle shaped and oval shaped pleomorphic cells in interstitium.16 It is extremely rare and easily misdiagnosed since the morphology is similar to that of PANP. A large number of dilated thin-walled blood vessels are distributed in clusters, with different lumen sizes. Pink staining and amorphous protein like substance can be seen under the intima of the vessels. Hyaline degeneration can be seen on the wall of the vessels, extending from the vessels to the interstitium around the vessels. Organized and recanalized thrombus can be seen in some vessels. Pleomorphic tumor cells are interspersed between blood vessels in sheet or bundle shape. The tumor cells are spindle, round or oval, with pleomorphic nuclei. Giant cells of pleomorphic tumor can be seen, but mitosis is rare. It is a characteristic histological change, with pseudoinclusions in the nucleus. Erbolat KQ et al. thought that vimentin and CD3417,18 were positive in PHAT tumor cells, were positive in some of them, and low Ki67 PI suggested that tumor cells had low proliferative activity (<5%).19 Imaging findings showed that surrounding bone were damaged, sometimes discontinuously, in both. However, histological examination showed that PHAT appeared to contain more hyalinized and degenerated thin-walled dilated blood vessels and marked stomal atypia, which was helpful for distinguishing.

Complete removal of PANP lesions by operation is the only effective treatment method, and the prognosis is good. On the contrary, PHAT is an intermediate ‒ locally aggressive soft tissue tumor with high recurrence rate. Therefore, extend local resection and long-term follow-up are recommended. In summary, understanding the clinical manifestations, imaging and pathological features are essential for making proper diagnosis and treatments between the two diseases in the nasal cavity and sinuses.

PANP is a clinically rare tumor which may simulate malignancy lesion. Recognizing of characteristic features in these thirteen patients would be beneficial to avoid misdiagnosis and unnecessary aggressive treatment.

There is no funding for this work.

The author declares no conflicts of interest.