**4.1 Inflammatory polyps**

Inflammatory polyps are certainly the most common lesions that are confused with REAHs.

The most notable clinical differences between REAHs and inflammatory polyps are the location and their gross appearance.

Inflammatory polyps are typically the clinical manifestation of a sinonasal polyposis. Nasal polyps are rarely isolated. They are multiple and bilateral and usually extrude from the middle and superior meati. They are rarely attached to the posterior septum. REAHs originate specifically from the olfactory cleft.

Nasal polyps are usually edematous and not indurated. On microscopy, both lesions can show fibroblastic and vascular proliferation, stromal edema, a mixed inflammatory cell infiltrate, and seromucinous gland proliferation. However, inflammatory polyps do not have florid adenomatoid proliferation and stromal hyalinization which, when present, favor REAHs (**Figures 6–9**).

**Figure 6.** *Macroscopic and endoscopic view of a nasal polyp.*

**4.2 Schneiderian papillomas**

**Figure 9.**

**57**

**Figure 8.**

This is the second important differential diagnosis of REAHs.

*Inflammatory polyp showing inflammatory stroma without hyalinization.*

*Inflammatory polyp with edematous inflammatory stroma and single-layered glands.*

*REAHs and REAH-Like Lesions: Underdiagnosed lesions Often Misconfused with Nasal Polyps*

*DOI: http://dx.doi.org/10.5772/intechopen.90327*

Schneiderian papillomas are benign epithelial neoplasms of the sinonasal tract.

They are classified in three types: exophytic/fungiform papilloma, endophytic/ inverted papilloma, and oncocytic/cylindrical cell papilloma. The inverted type is

Their annual incidence ranges between 0.2 and 1.5/100,000 people per year.

**Figure 7.** *Endoscopic view: right and left nasal cavity: presence of nasal polyps in the middle and superior meati.*

*REAHs and REAH-Like Lesions: Underdiagnosed lesions Often Misconfused with Nasal Polyps DOI: http://dx.doi.org/10.5772/intechopen.90327*

**Figure 8.** *Inflammatory polyp with edematous inflammatory stroma and single-layered glands.*

**Figure 9.** *Inflammatory polyp showing inflammatory stroma without hyalinization.*
