The uncinate process is a very important surgical landmark in the lateral nasal wall for endonasal sinus surgery. Although considered part of the ethmoid labyrinth since it derives from the descending portion of the first ethmoturbinal, the uncinate process is typically discussed when addressing the maxillary sinus because of its intimate relationship with the maxillary ostium. The uncinate process is a crescent-shaped bony structure that typically projects from posteroin-ferior (at the palatine bone and inferior turbinate) to anterosuperior where it runs along the lateral nasal wall attaching to the ethmoid crest of the maxilla, the lacrimal bone, the skull base or the lamina papyra-cea. Its anterior-inferior margin has no bony attachments, and posteriorly it attaches to the ethmoid process of the inferior turbinate (Fig. 2.4) . Its anterior convex part forms the anterior boundary of the (anterior) ostiomeatal complex, where the maxillary, anterior ethmoid and frontal sinuses drain. It endo-scopically hides the hiatus semilunaris, which could fairly be represented by the space between the unci-nate and the ethmoid bulla. The uncinate process can be displaced medially by polypoid disease or laterally against the orbit as in maxillary sinus hypoplasia. Removing the uncinate process is the first step of most endoscopic sinus surgeries. When performing this, one must keep in mind the anterior insertion of the uncinate process in order to avoid injuries to the medial orbital wall (lamina papyracea). This step usually reveals the natural ostium of the maxillary sinus. The superior border of the maxillary sinus ostium identifies the level of the orbital floor.
The maxillary sinus is the largest and most constant of the paranasal sinuses. It is the first sinus to develop in utero. After birth, it undergoes two periods of rapid growth, between birth and 3 years of life, then between ages 7 and 18 years. The maxillary sinus has a pyramidal shape with an anterior wall corresponding to the facial surface of the maxilla. Its posterior bony wall separates it from the pterygomaxil-lary fossa medially and from the infratemporal fossa laterally. Its medial wall does not contain any bone; it is formed by the middle meatus mucosa, a layer of connective tissue and the sinus mucosa . This is best recognized at the level of the posterior fontanelle which corresponds to the area between the tails of the middle and inferior turbinates, behind the hiatus semilunaris and under the ethmoid bulla. The poste rior fontanelle can have an opening to the maxillary sinus, the accessory ostium, which could be mistaken for the natural ostium during ESS if an incomplete uncinectomy is performed (Fig. 2.4). A smaller anterior fontanelle is located between the anterior part of the uncinate superiorly and the insertion of the inferior turbinate inferiorly. The floor of the maxillary sinus is formed by the alveolar process of the maxillary bone and the hard palate. It lies at the same level of the floor of the nose in children, and 5-10 mm under the floor of the nose in adults . The roof of the maxillary sinus corresponds to the floor of the orbit, and frequently shows a posteroanterior bony canal for the distal part of the second branch of the trigeminal nerve. The most common anatomical variation in the maxillary sinus is the infraorbital ethmoid cell, or Haller cell; Haller cells are pneumatized ethmoid cells that project along the floor of the orbit, arising most often from the anterior ethmoids [11, 14]. They can in some cases compromise the patency of the maxillary sinus infundibulum, and in other cases can be involved in the chronic polypoid disease, which will mandate opening them. In addition to this, removing the infraorbital ethmoid cell will allow an accurate identification of the floor of the orbit and the posterior wall of the maxillary sinus, which represent reliable surgical landmarks in the presence of advanced disease or distortion of the middle me-atal anatomy.
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