Antrochoanal Polyp Ct

Pattern of Nasal Polyposis

The pattern of nasal polyposis is characterized in most cases by bilateral involvement of middle meati, ethmoid infundibula (often widened), and paranasal cavities. Inflammatory polyps most frequently arise in the middle meatus from the mucosa investing the middle turbinate, the ethmoid infundibu-lum, and the uncinate process. They also originate from the anterior part of ethmoid bulla or frontal recess. At CT, they appear as solid lobulated lesions filling the ethmoid, nasal fossae and sinusal cavities, in most cases with bilateral extension. Bone remodeling is associated, triggered by mechanical pressure exerted by the polyps but also by the local release of inflammatory mediators and by bacterial invasion of bone and periosteum (GiACChi et al. 2001). This

Posterior Ethmoids
Fig. 6.11. Sphenoethmoid recess pattern. Mucosal thickening along the path of sphenoethmoid recess (dotted line), thickened mucosa, and retained secretions within posterior ethmoid cells and sphenoid sinus (asterisks)

process is a complex balance between the activity of osteoblasts and osteoclasts. As a result, thinning and displacement of subtle bone structures such as ethmoid labyrinth and lamina papyracea (often exhibiting inversion of its normal medial convexity) may be observed along with sclerosis of thicker sinusal walls, such as posterolateral maxillary sinus wall (Fig. 6.12a).

Two additional signs are described as common features of sinonasal polyposis. (1) Widening of ethmoid infundibulum can be observed in several different conditions, including antrochoanal polyp and inverted papilloma. The specificity of this finding, however, is increased by bilateral presentation. (2) Truncation of middle turbinate (bilateral in up to 80% of cases) is easily recognized on CT scans as an amputation of the more distal, bulbous part, the vertical lamella usually being spared. In a series of 100 patients (LiANG et al. 1996) affected by chronic rhinosinusitis, this sign was observed exclusively in the subgroup with sinonasal polyposis, in 58% of cases.

MR signal pattern of inflammatory polyps does not differ from that of mucosal cysts, it is composed of hyper T2 signal and a combination of hyperinten-sity (mucosa) and hypointensity (edematous stroma) on contrast-enhanced T1 (Fig. 6.12b).

Even though bone changes and bilateral pattern of growth are quite typical, it must be emphasized

Nasal Polyp

Fig. 6.12a,b. Nasal polyposis. Coronal CT (a) and Gd-DTPA SE T1 (b) scans through the anterior ethmoid. Nasal fossae, maxillary sinuses and ethmoid cells are completely filled by polyps. Dehiscence and remodeling of bone structures of the lateral nasal walls; pressure exerted by polyps remodels and laterally displaces both laminae papyraceae [arrows in (a)]. MR better delineates the hypointense stromal component of polyps [black arrows in (b)], deep to the mucosal surface. Within the maxillary sinus the folds of hypertrophic mucosa are detected [white arrows in (b)]

Fig. 6.12a,b. Nasal polyposis. Coronal CT (a) and Gd-DTPA SE T1 (b) scans through the anterior ethmoid. Nasal fossae, maxillary sinuses and ethmoid cells are completely filled by polyps. Dehiscence and remodeling of bone structures of the lateral nasal walls; pressure exerted by polyps remodels and laterally displaces both laminae papyraceae [arrows in (a)]. MR better delineates the hypointense stromal component of polyps [black arrows in (b)], deep to the mucosal surface. Within the maxillary sinus the folds of hypertrophic mucosa are detected [white arrows in (b)]

that density/signal pattern of nasal polyps is not completely specific; therefore several authors recommend thorough evaluation of surgical specimens.

A peculiar variant of sinonasal polyp is represented by antrochoanal polyp. This lesion arises in the maxillary sinus and protrudes in the middle meatus (through its natural drainage pathway or through an accessory ostium), where it extends between the middle turbinate and the lateral nasal wall. In its further posterior growth, the lesion typically reaches the choana. CT density of antrochoanal polyp is low (fluid-like), MR appearance resembles that of inflammatory polyps (Figs. 6.13, 6.14). Sphenochoanal and ethmoidochoanal polyps are described as extremely rare variants.

As a consequence of their natural history (growth through ostia), all sinochoanal polyps are subject to vascular compromise, because the waist of the polyp may be strangled as it passes through constrictive ostia. When this occurs, the intranasal portion of the sinochoanal polyp shows dilation and stasis of feeding vessels combined with edema. This vascularly compromised part of the lesion exhibits bright enhancement, possibly due to stasis in dilated vessels and is referred to as an angiomatous polyp (Batsakis and Sneige 1992; de Vuysere et al. 2001) (Fig. 6.14). Prolonged vascular damage may induce complete necrosis of the polyp, finally resulting in autopolypec-tomy (Pruna 2003).

Antrochoanal Polyp Scan
Fig. 6.13a,b. Antrochoanal polyp. Axial (a) and coronal (b) CT scan. Polypoid lesion occupies the left maxillary sinus, protruding into the nasal fossa and, through the choana, in the nasopharynx (arrows). Note in (b) the low density of the lesion
Scan Sinus Polyps

Fig. 6.14a,b. Antrochoanal polyp. Coronal SE T2 (a), axial Gd-DTPA SE T1 (b). The maxillary sinus is occupied by a lesion protruding through an accessory ostium into the middle meatus and then posteriorly reaching the choana. The signal pattern of the lesion resembles that of a common nasal polyp. The part of the lesion passing through the ostium (arrows) shows hypointense T2 signal and vivid enhancement, possibly due to stasis of contrast agent within dilated vessels. This vascularly compromised component of the lesion is referred to as an angiomatous polyp

Fig. 6.14a,b. Antrochoanal polyp. Coronal SE T2 (a), axial Gd-DTPA SE T1 (b). The maxillary sinus is occupied by a lesion protruding through an accessory ostium into the middle meatus and then posteriorly reaching the choana. The signal pattern of the lesion resembles that of a common nasal polyp. The part of the lesion passing through the ostium (arrows) shows hypointense T2 signal and vivid enhancement, possibly due to stasis of contrast agent within dilated vessels. This vascularly compromised component of the lesion is referred to as an angiomatous polyp

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  • fre-qalsi
    How to reach antrochoanal polyp?
    7 years ago

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