Image Analysis of Sinonasal Neoplasms
It is often difficult for the radiologist to hone down on a particular histologic diagnosis because of the marked overlap of the imaging appearance of different tumors on CT and MRI.111 The major contribution by the radiologist is an accurate mapping of the tumor extent in the context of an understanding of the anatomic sites that will influence or alter surgical resection, treatment planning, and prognosis. In the setting of sinonasal malignancies, a combination of CT and MRI is usually acquired.69,70,73,74,112 Potential areas of tumor extension that must be assessed in all patients with sinonasal malignancies include intracranial spread (the anterior and middle cranial fossa), the palate, the orbits, the pterygopalatine fossa, and the skull base.22–24,111,113
Histologic specificity is not possible with MRI or CT techniques except perhaps in some cases of melanoma. In the majority of melanomas that contain melanin, the neoplasms may be hyperintense to gray matter on unenhanced T1-weighted images, with more variable signal characteristics on a corresponding T2-weighted MRI.114–119
Differentiating Secretions and Inflammatory Changes from a Tumor
One of the advantages of MRI over CT is its ability to help discern complex sinonasal secretions and inflammatory disease from a tumor ( Fig. 3.2A,B ).7,73,76,102,120–124 Secretions and mucosal disease frequently have a high water content yielding high signal intensity on T2-weighted images with peripheral enhancement ( Fig. 3.3A,B ).
A combination of T1- and T2-weighted images is extremely useful in distinguishing secretions and mucosal inflammation from neoplasm.122 Both pulse sequences are important due to the marked variability in the signal intensity of sinonasal secretions, which is the result of variable protein concentrations, the presence and extent of mobile water protons, and viscosity. The changes in signal intensity associated with increasing protein concentrations are likely due to extensive cross-linking of the glycoproteins present within hyperproteinaceous secretions. As a result, the relative amount of mobile water protons decreases. In the presence of low protein concentrations (less than 10%) and high free water content, secretions in the paranasal sinuses are typically hypointense on T1-weighted images and hyperintense on T2-weighted images.57 As the protein concentration increases, secretions on T1-weighted images become more hyperintense. When concentrations approach 20 to 25%, secretions typically are hyperintense on both T1-weighted and T2-weighted sequences. When protein concentrations exceed 25%, they are hyperintense on T1-weighted and hypointense on T2-weighted images ( Fig. 3.18A,B ). Finally, when protein concentrations are extremely high (exceeding 28%) such as is seen in aggressive fungal infections, they are hypointense on both T1-and T2-weighted sequences and can mimic an “aerated sinus” ( Fig. 3.19A,B ).
The hallmark of malignancies involving the sinonasal cavity is the presence of osseous destruction most commonly seen with carcinomas ( Fig. 3.20 ).111 Bone involvement is seen in ~80% of CT scans assessing sinonasal squamous cell carcinomas. Esthesioneuroblastomas occur in the upper nasal cavity/ethmoid vault, arising from the olfactory nerves. They have a marked propensity for eroding the cribriform plate and extending intracranially.121,125 Although less common, bone destruction may also be seen with lymphomas ( Fig. 3.21A ), metastases, and sarcomas.
Sclerosis secondary to a tumor is rare. The presence of such is normally related to coexistent chronic inflammatory changes. Although uncommon, osteomyelitis may occur and is usually associated with rarefaction and sclerosis of bone. Calcification of sinonasal tumors is uncommon. Although prior literature has suggested that the presence of calcification with certain tumors is typical, it is more likely that in many cases that the findings interpreted as calcifications actually corresponded to fragmented bone.126