The medial Orbit

The medial orbital wall is composed of several bones: the frontal process of the maxilla, the lacrimal bone, the lamina papyracea of the ethmoid, and part of the lesser wing of the sphenoid. In terms of function, the medial orbit can be divided into anterior, middle, and posterior thirds.

Anterior One Third of the Medial Orbital Wall. The medial orbital rim and the anterior one third of the medial orbit comprise the frontal process of the maxilla, the maxillary process of the frontal bone, and the lacrimal bone. The lacrimal fossa for the lacrimal sac lies between the anterior and posterior lacrimal crest. The anterior crest is a continuation of the frontal process of the maxilla. The posterior lacrimal crest is an extension of the lacrimal bone. The bone of the lateral nasal wall contains the nasolacrimal duct, which enters the nasal cavity through the inferior meatus located beneath the inferior turbinate.

Middle One Third of the Medial Orbital Wall This part of the medial orbital wall, largely made of the lamina papyracea of the ethmoid bone, is thin, but is reinforced by the buttress effect of the ethmoid air cells. The only vascular structures of any significance are the anterior and the posterior ethmoidal arteries. The foramina for the anterior and posterior ethmoid arteries and nerves are found in, or just above, the frontoethmoid suture line at the level of the cribriform plate. The anterior ethmoid foramen is located approximately 24 mm posterior to the anterior lacrimal crest (4) (Fig. 6-6). The posterior ethmoid foramen or foramina (25% are multiple) are located approximately 36 mm posterior to the anterior lacrimal crest (4). The optic canal is located approximately 42 mm posterior to the anterior lacrimal crest. The distance between the posterior ethmoidal artery and the optic nerve is variable, but it is never less than 3 mm (4).

Figure 6- 6 Medial orbital wall of the skull. Note the position of the anterior and posterior ethmoidal foramina (arrows). They are not located at the most superior portion of the orbit but at the level of the cribriform plate.

Posterior One Third of the Medial Orbital Wall. The posterior part of the orbit is made of thick bone surrounding the optic foramen and superior orbital fissure.

TECHNIQUE

The coronal approach can be used to expose different areas of the upper and middle face, The layer of dissection and the amount of exposure depend on the particular surgical procedure for which the coronal approach is used. In some instances, it may be prudent to perform a subperiosteal elevation of the flap from the point of incision. The periosteum is freed with a scalpel along the superior temporal lines as one proceeds anteriorly with the dissection, leaving the temporalis muscle attached to the skull. In most cases, however, dissection and elevation of the flap are in the easily cleaved subgaleal plane. For illustrative purposes, the following description is that of complete exposure of the upper and middle face, including the zygomatic arch, using a subgaleal dissection for most of the flap elevation.

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