Antrochoanal polyps arise from the maxillary sinuses and are the much less common, ethmoidal polyps arise from the ethmoidal sinuses.
Antrochoanal polyps are usually single and unilateral whereas ethmoidal polyps are multiple and bilateral.
Above the ethmoidal crest is a narrow, horizontal groove, which forms part of the superior meatus.
It is formed by a mucous membrane that is covering the ethmoidal crest of the maxilla.
In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells.
It passes through the posterior ethmoidal foramen, with the posterior ethmoidal artery.
It is the gloomy area beneath the lac(rimal) and ethmoidal bones in the image.
The nerve is the continuation of the nasociliary nerve after it enters the anterior ethmoidal foramen into the anterior ethmoidal air cells.
