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The risk of lymphatic metastasis in sinonasal malignancies depends on the site, extent of tumor spread, and histology (Fig. 5). As the sinonasal tract is thought to have limited capillary lymphatics [16], the incidence of regional metastasis is low, ranging between 4 and 15% [17, 18]. When the neoplasm is confined within a sinus cavity, nodal metastasis is more frequent in tumors arising from the maxillary sinus than from the ethmoid. A greater incidence of regional involvement, up to 50%, is reported when lymphatic-rich areas adjacent to the sinuses are invaded, like the masticatory space or the skin. Among the different histologies, nodal metastases are more frequently observed in olfactory neuroblastoma (ONB; up to 43%), mucosal malignant melanoma, and squamous cell carcinoma [19, 20].

Fig. 5. Adenosquamous carcinoma. a The patient was examined for a large lymph node metastasis at level 2 with extranodal extent and no primary. The sternocleidomastoid muscle is infiltrated (black arrows). The right common carotid artery is displaced medially. A node-to-vessel contact of less than 180° is present (white arrows). b In the axial TSE T2 sequence, low-intensity tissue is detectable in the posterior ethmoid cells of both sides (black arrows on the right, white arrows on the left). At endoscopic surgery both ethmoid lesions were neoplastic; no connection between the two sides was demonstrated.

In addition to the upper jugular and facial nodes, sinonasal malignancies drain to the retro-latero-pharyngeal nodes (RLPN). While CT and MRI yield similar results in assessing cervical lymph nodes, MRI has been found to be significantly more sensitive than CT in detecting abnormal RLPN [21]. Findings suggesting RLPN metastasis include a short diameter greater than 5 mm or the presence of intranodal necrosis (a central area showing high intensity on T2W sequence and low intensity on postcontrast T1W sequences) [22]. Both cervical and RLPN metastases are a poor prognostic factor for decreased overall survival and locoregional control [23]. When MRI is used to evaluate the local tumor extent, contrast-enhanced CT or an ultrasound examination can be used to evaluate the lymph nodes of the neck. An advantage of the ultrasound examination is easy sampling of suspicious nodes via FNAC (fine-needle aspiration cytology).

Distant metastases are uncommon, ranging from 10 to 15%, and they depend on the histology [1, 24, 25]. Sinonasal mucosal melanomas have a worse prognosis than other head and neck sites [18, 26]. While in these patients the incidence at the time of diagnosis is <10%, up to 40–50% of patients will develop distant metastasis in the lung, brain, liver, and bone during follow-up [27]. PET-CT is indicated in the work-up of distant metastasis, particularly in very aggressive histologic types such as mucosal melanoma [28].