Radiology Quiz Case 1: Diagnosis

Diagnosis: Sinonasal idiopathic inflammatory pseudotumor (IIP) with orbital invasion

In the head and neck region, IIP most commonly involves the orbit and rarely involves the paranasal sinuses. The common symptoms of the sinonasal IIPs are pain around the involving sinus, nasal obstruction, and hemorrhagic rhinorrhea. Our patient had only orbital symptoms, such as periorbital edema, proptosis, global displacement, and binocular diplopia, with limitation on ocular motility; however, he had no nasal symptoms or painful cheek swelling. The mass was clinically silent until it invaded the orbital area, with periorbital edema, proptosis, and extraocular muscle involvement.

Computed tomography with moderate enhancement showed a homogeneous mass. Classically, orbital IIP rarely involves the orbital bony walls. However, the sinonasal IIP has a more aggressive appearance on imaging than its counterpart in the orbit.¹ The imaging findings can mimic a malignant neoplasm and lead to unnecessary radical surgery.^{2 - 3} The computed tomographic findings in our case showed an irregular mass filling the sinonasal cavity. Bony erosion and tumor invasion of the left medial inferior orbit were highly suggestive of a malignant process. Transnasal biopsy of the nasal mass revealed lymphoid hyperplasia in the stroma. Oral prednisolone was initially prescribed for 1 week; however, the ocular symptoms showed little improvement. Endoscopic sinus surgery was subsequently performed.

Idiopathic inflammatory pseudotumor of the cervicofacial region is more often involved secondary to orbital pseudotumor with sinonasal or facial manifestations. Primary sinonasal IIP with orbital involvement is rare. Idiopathic inflammatory pseudotumors of the sinonasal tract with orbital involvement should be distinguished from fungal infection, granulomatous inflammation, collagen vascular disease, sarcoidosis, sinus neoplasia, metastatic tumors, lymphoma, and bacterial cellulitis that has spread from the sinus to the orbit. Lymphoma is the most difficult lesion to exclude by imaging and pathologic analysis. Only pathologic examination and flow cytomety can help to differentiate IIP from lymphoma.

High-dose corticosteroid therapy for 2 to 4 weeks has been recommended to treat IIPs. Lesions with lymphoid follicles tend to be more responsive to steroid therapy, whereas more mature lesions have a greater component of fibrous tissue and will show lesser response. In this case, the ocular symptoms initially showed little improvement with oral prednisolone therapy. This lack of response could have been the result of the prominent fibrosis component of the tumor. Ruaux et al⁴ reported that sinonasal IIPs are less responsive to treatment with corticosteroids than orbital IIPs. Som et al¹ also suggested that surgery should be performed in cases with poor response to steroid therapy. When surgery is indicated, the excision should be as complete as possible, while avoiding the radical resection that is often used in oncology. Radiotherapy and chemotherapy may be considered in patients with IIP who are steroid resistant or intolerant.^{3 ,5}

Idiopathic inflammatory pseudotumors of the paranasal sinuses can masquerade as a malignant neoplasm with bony erosion on imaging studies. It is important for the head and neck surgeon to be familiar with such disease entities and to provide adequate treatment modalities.

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