The periosteum of the orbit (periorbita) is an important anatomic structure of the orbit. It represents the only soft tissue barrier between the paranasal sinuses and orbital contents. It is a relatively tough fibrous membrane that is generally loosely adherent to the surrounding bones except at the anterior orbital margin, lacrimal crests, margins of the fissures, and the canals.<sup>29 McNab A.A., Wright G.E. Orbitofrontal cholesterol granuloma Ophthalmology 1990 ;  97 : 28-32

Cliccare qui per andare alla sezione Riferimenti, 35 Reeh M.J., Wobij J.L., Wirtschafter J.D. Ophthalmic Anatomy: A Manual with Some Clinical Applications San Francisco: American Academy of Ophthalmology (1981).  11-54

Cliccare qui per andare alla sezione Riferimenti, 36 Diseases of the Orbit Philadelphia: JB Lippincott (1988). 

Cliccare qui per andare alla sezione Riferimenti</sup> Posteriorly, it is continuous with the dura of the optic nerve and the dura surrounding the superior orbital fissure,<sup>27 Mafee M.F., Putterman A., Valvassori G.E. , e al. Orbital space occupying lesions: Role of computed tomography and magnetic resonance imaging Radiol Clin North Am 1987 ;  25 : 529-559

Cliccare qui per andare alla sezione Riferimenti, 36 Diseases of the Orbit Philadelphia: JB Lippincott (1988). 

Cliccare qui per andare alla sezione Riferimenti</sup> and anteriorly with the periosteum of the orbital margins. Thus, surgery or trauma posteriorly may result in cerebrospinal fluid leaks.<sup>36 Diseases of the Orbit Philadelphia: JB Lippincott (1988). 

Cliccare qui per andare alla sezione Riferimenti</sup> The periorbita can be easily stripped from the bone except at the suture lines, where it passes through to fuse with the periosteum on the other side. In descriptive terms, the orbit has been divided into extraperiosteal, subperiosteal, extraconal, and intraconal spaces.

The subperiosteal compartment of the orbit, a potential space, is an important entity due to its unique anatomy, location, and susceptibility to various pathologic processes, such as hemorrhage, infection, infiltration of lymphoproliferative disorders, infiltration of en plaque meningiomas, and metastasis. Early diagnosis and intervention may be crucial in preventing significant morbidity in many cases. CT and MR imaging have contributed greatly to our understanding of orbital disorders. Both techniques are excellent for defining abnormalities within the orbital subperiosteal region. The detection of these lesions is based on tissue density and tissue intensity as provided by MR imaging. This article discusses the role of CT and MR imaging in a variety of more important subperiosteal lesions and aids the radiologist and the clinician to diagnose correctly orbital subperiosteal lesions.