![]() The orbital floor is the roof of the maxillary sinus. It is formed mainly by the orbital plate of the maxilla with contributions from the zygoma anterolaterally and the palatine bone at its most posterior limit. The floor ( Figure 5) is triangular and slopes gradually upwards to merge almost imperceptibly with the medial wall at the maxilloethmoid suture. The medial wall articulates with the floor at the maxillo-ethmoid suture, which marks the position of the thick inferomedial bony strut which is usually left intact anteriorly to support the globe and prevent hypoglobus following orbital decompression. The anterior and posterior ethmoidal nerves and vessels leave the orbit via their respective foramina located in the fronto-ethmoid suture and the vessels should be clipped or cauterized to avoid potentially devastating orbital haemorrhage in the course of extraperiosteal medial wall dissection. Removal of bone above this suture carries the risk of cerebrospinal fluid leakage owing to exposure of the dura of the frontal lobe. The medial wall articulates with the roof at the fronto-ethmoid suture, which marks the upper limit of safe bone removal during medial wall decompression. 3 The thick bone of the sphenoid body forms the most posterior part of the medial wall, adjoining the optic canal. The lamina papyracea fractures readily follow blunt orbital trauma and is also readily breached in the course of ethmoid sinus surgery, exposing the orbit to the risk of inadvertent surgical injury. This paper-thin bone overlying the ethmoid sinus facilitates the spread of infection, in cases of ethmoid sinusitis, into the orbit with subperiosteal abscess formation and/or orbital cellulitis ( Figure 4). The vast majority of the medial wall is comprised of the lamina papyracea. The latter is a well-defined ridge on the thin lacrimal bone, which forms part of the lateral wall of the nose and overlies the root of the middle turbinate. At its anterior aspect, it contains the lacrimal fossa which is bounded by the anterior and posterior lacrimal crests. The medial wall ( Figure 3) is roughly rectangular and extends from the anterior lacrimal crest (frontal process of the maxilla) to the orbital apex.
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