Fig. 2.1
The main views of the skull: (a, b) the anterior and posterior views. The auricular vertical plane runs parallel to the X-ray film holder, while the median sagittal plane and the horizontal plane run perpendicular to it. (c) The lateral view. The median sagittal plane is oriented parallel to the X-ray film holder, while the auricular vertical and horizontal planes are oriented perpendicular to it. (d, e) The parietal (d) and mental (e) axial views, when the horizontal plane is oriented parallel to the X-ray film holder plane, while the sagittal and the auricular vertical planes are oriented perpendicular to it. (f, g) Anterior (f) and posterior (g) semiaxial views, when the horizontal and auricular vertical planes are oriented at an angle of 45° with respect to the X-ray film holder, while the median sagittal plane is strictly perpendicular to it. If position (g) is infeasible, position (h) is used
X-ray imaging of the skull using the anteroposterior view provides a general overview of the condition of the calvarial bones, cranial sutures, and temporal pyramids. It is difficult to interpret the condition of the orbit because the images of the bones of the skull base overlap those of the upper sections of the orbit. However, the orbital opening and the orbital floor are clearly discernible (Fig. 2.2).
Fig. 2.2
X-ray image of the skull in the anteroposterior view (nasofrontal position): The calvarial bones (1) and cranial sutures (2) are clearly discernible. The image of the temporal pyramids (3) overlaps that of the orbit (4), resulting in fragmentary image of the orbital opening (shown with small triangular arrows) and the infraorbital margin in particular (small arrows). The superior orbital wall is imaged rather clearly. Furthermore, frontal sinuses (5), cribriform plate of the ethmoidal labyrinth (6), nasal cavity (7), and maxillary sinuses (8) are seen in the image
X-ray imaging of the skull in the posteroanterior view is mainly performed for patients with severe head injury. Such orbital structures as wings of the sphenoid bone and the superior orbital fissures are clearly seen in the images.
X-ray imaging of the skull using the lateral view also presents an overview and is rather useful to assess the condition of the calvarial bones and the skull base (but not the facial skeleton). Paranasal sinuses, sella turcica, anterior and posterior clinoid processes, nasopharynx, and lamina cribrosa of the ethmoid bone are clearly discernible in the images. This view presents the best image of the lateral margin and the superior orbital wall. It is difficult to interpret the condition of the orbital floor using the lateral view due to its S-shaped profile and elevation toward the orbital apex. Also, the overlap of the images of both orbits results in several contours of the orbital floor seen on a single image [1] (Fig. 2.3).
Fig. 2.3
X-ray image of the skull in the lateral view: Frontal sinuses (1), jugum sphenoidale (3), sella turcica (4), anterior (5) and posterior (6) clinoid processes, and sphenoidal sinus (7) are seen in the image. This view provides the best image of the lateral margin and the orbital roof (2). It is difficult to interpret the condition of the orbital floor (shown with arrows) using the lateral view due to its S-shaped profile, elevation toward the orbital apex, and summation of the images of both orbits, resulting in several contours of the orbital floor seen in an image
A standard X-ray examination of the orbit and periorbital structures includes occipitofrontal (Caldwell’s) projection, nasomental projection, Waters anterior semiaxial (occipitomental) projection, and lateral and parietal (submentovertex) projections (Table 2.1).
Table 2.1
The main X-ray projections used to diagnose orbital fractures
Projection | Anatomical structure being visualized | Pathological changes being visualized |
|---|---|---|
Occipitomental | The anterior two-thirds of the orbital floor, the zygomatic arch | Fractures of the superior and inferior orbital walls with vertical displacement of the fragments |
Maxillary sinus | Sinusitis, hemosinus | |
Occipitofrontal | Frontal sinus, ethmoidal labyrinth | Hemosinus, mucocele, fracture of sinus walls |
Innominate line | Fracture of the medial and lateral orbital walls | |
Sphenoid bone | Lateral wall fracture | |
Posterior one-third of the orbital floor | Blow-out fracture | |
Lateral | Superior orbital wall | Fracture of the superior wall |
Sella turcica | Pituitary disorders | |
Basal (submentovertex) | Sphenoid sinus and ethmoidal labyrinth | Fracture |
Lateral orbital wall | Lateral orbital wall fracture | |
Zygomatic arch | Fracture of the zygomatic arch | |
Rhese’s oblique anterior | Optic canal | Fracture of canal walls |
In addition to the aforementioned standard projections, three specialized ones are used: nasal projection, frontal protuberance projection, and Rhese’s oblique anterior (posterior) projection (Fig. 2.4).
Fig. 2.4
Projections used for X-ray imaging of the orbit: CM canthomeatal (or the orbitomeatal) line connecting the lateral canthus and the external acoustic foramen (the physiological horizontal line), CXB central X-ray beam. (a) Caldwell’s occipitofrontal (anterior fronto-occipital) projection. A prone patient touches the X-ray film holder with his/her nose tip and forehead. The angle between the X-ray beam direction and the canthomeatal line (15–23°) moves the shadow from the temporal bone downward from the image of the orbit. (b) Nasomental projection. The nose and chin of a prone patient are tightly pressed against the X-ray film holder. (c) Waters anterior semiaxial (occipitomental) projection. A prone patient touches the X-ray film holder only with his/her chin; the nose tip lies 0.5–1.5 cm above the X-ray film holder. The angle between the canthomeatal line and the central X-ray beam is 37–45°. (d) The basal (axial, submentovertex) projection. A cushion is placed under the shoulders of a patient lying supine so that his/her head tilted back touched the X-ray film holder with the bregma, while the infraorbitomeatal line (IM) is parallel to the X-ray cassette and perpendicular to the central X-ray beam. (e) Rhese’s oblique anterior projection. The head of a patient lying prone is positioned in such a manner that the superciliary area, the zygomatic bone, and the nose tip were pressed against the X-ray film holder. The beam is centered for the opposite parietal protuberance; the sequential images of both orbits are obtained strictly symmetrically
Caldwell’s occipitofrontal projection (1918) allows one to study the contours of the orbital opening, the lacrimal sac fossa, and the medial and lateral orbital walls but not the infraorbital margin. This is because it is difficult to assess the infraorbital margin because the shadow from the inferior orbital wall overlaps the margin with the anterior one-third of the inferior orbital wall imaged below the margin, the middle one-third lies at its level, and the posterior one-third imaged above the margin [2]. In this view, such anatomical structures as the superior and inferior orbital fissures and wings of the sphenoid bone are overlapped by temporal pyramids (Figs. 2.2 and 2.4a).
An image using the nasomental projection with patient’s nose being tightly pressed to the X-ray cassette is an overview image of the orbits in the anteroposterior view, which allows one to compare the shape and size of margo orbitalis. Furthermore, this projection is the one to be used when examining the frontal and maxillary sinuses and the ethmoidal labyrinth. Finally, facial bones are clearly visualized in the nasomental projection (Figs. 2.4b and 2.5).
Fig. 2.5
X-ray image of the orbits in anteroposterior projection (Caldwell’s occipitofrontal projection) allows one to assess the contours of the orbital opening, the lacrimal sac fossa (1), and the medial (2) and lateral (3) walls of the orbit. It is difficult to assess the infraorbital margin (4), since it is overlapped by the shadow of the inferior wall (with the anterior one-third of the inferior wall lying above the margin, the middle one-third lying at its level, and the superior one-third lying above the margin). (5) Innominate line, (6) the greater wing of the sphenoid bone, (7) ethmoidal labyrinth, (8) frontal sinus, and (9) margin of the pyramid of the temporal bone
The Waters and Waldron (1915) semiaxial occipitomental projection is indispensable for assessing the condition of the anterior portions of the medial wall, the roof and floor of the orbit, the zygomatic bones, the lesser wing of the sphenoid bone, the infraorbital foramen, as well as the maxillary sinuses and the ethmoidal labyrinth (Figs. 2.4c and 2.6). Due to the clear image of the superior orbital wall, as well as the anterior and middle one-thirds of the inferior orbital walls, the projection is used to visualize the vertically displaced roof and floor fragments, including the diagnosis of blow-out and blow-in fractures of the orbital roof and floor. When interpreting an image, one should bear in mind that the image of the orbital floor is 10 mm below the contour of the infraorbital margin due to specific features of the projection.
Fig. 2.6
X-ray imaging in the anterior semiaxial (occipitomental) projection according to Waters and Waldron (1915): Since the shadow of the pyramid of the temporal bone is moved downward, the projection clearly visualizes the medial (1), inferior (2), and superior (3) walls of the orbit, the infraorbital margin (4) and the infraorbital canal (5), the frontozygomatic suture (6), the zygomatic arch (7), the lesser wing of the sphenoid bone (8), as well as the frontal (9) and maxillary sinuses (10) and ethmoidal labyrinth (11). (12) Innominate line (linea innominata), (13) cribriform plate of the ethmoid bone, and (14) crista galli
Thus, the occipitomental and occipitofrontal projections need to be used to perform a thorough analysis of the condition of the inferior orbital wall.
The Schuller’s (1905) and Bowen’s (1914) basal (axial, parietal, submentovertex) projection visualizes the lateral wall of the orbit and maxillary sinus along its entire length, the nasopharynx, the pterygoid processes of the sphenoid bone, the pterygopalatine fossa, the sphenoidal sinus, and the ethmoidal labyrinth (Figs. 2.4d and 2.7). Meanwhile, the medial half of the orbits is overlapped by the image of the maxillary tooth row. The position cannot be used in patients with suspected injury of the cervical spine since it involves hyperextension of the neck.
Fig. 2.7
X-ray image of the orbit in the Schuller’s (1905) and Bowen’s (1914) axial projection: 1 zygomatic arch, 2 orbit, 3 infraorbital canal, 4 lateral wall of the orbit, 5 posterior wall of the maxillary sinus, 6 pterygoid process of the sphenoid bone, 7 sphenoidal sinus
The nasal projection (the anterior sagittal projection) is used to assess the condition of the wings of the sphenoid bone and the superior orbital fissures. Due to variability in structure of the sphenoid bone, it is difficult to analyze the images of the superior orbital fissures recorded using the nasal projection; therefore, special attention should be paid to the symmetry of the shape and size of the superior orbital fissures when assessing the images obtained from this projection. Mild orbital asymmetry is a normal variant, while more pronounced differences (more than 2 mm) are abnormal.
The frontal protuberance projection is obtained with a 3–4 cm-thick bandage placed under the nose tip and the central X-ray beam is directed anteriad from the external acoustic meatus. This projection visualizes the inferior orbital fissures.
Sequential X-ray imaging of the right and left orbits in the Rhese’s oblique anterior (posterior) projections (1911) is performed to visualize the optic canals (Fig. 2.4). The vertical and horizontal size of the optic foramen in the resulting image is normally 6 and 5 mm, respectively; the interorbital asymmetry of the size of optic foramina in 96% of patients is less than 1 mm. Both the increased vertical diameter (up to 6.5 mm and more) and obvious (more than 1 mm) asymmetry of optic foramina are indicative of a pathological state.
In addition to the optic foramen, the image displays the roots of the lesser wing of the sphenoid bone and the upper sections of the ethmoidal labyrinth. The pneumatized anterior clinoid process can be mistaken for the optic foramen. In order to avoid misinterpretation of the X-ray image, one should bear in mind that the optic foramen is viewed near the lateral margin of the jugum sphenoidale.
The Rhese’s projection is rarely used at this time because it has been replaced by the routine use of CT studies.
The interpretation of orbital X-rays is more difficult and complex than the interpretation of fractures at other locations because of the complex facial anatomy. The complex X-ray image of the facial skeleton, projection distortions, and the effect of overlapping of different bone structures add to the difficulties of interpretation. Orbital walls are thin flat compact structures; hence, the image formed on the film as a perpendicular X-ray beam passes through them is almost unidentifiable. The tangential orientation of X-rays is the only way to obtain a clear linear shadow with localization and configuration typical of each orbital wall.
Thus, the radiologic diagnosis of fractures of the bones of the middle facial area is often made by the interpretation of indirect signs such as the altered smoothness of the contour of the orbit, zygomatic arches, etc. and the deformation of the contour of the orbital and paranasal sinuses or the bone surface. The radiologic interpretation in other locations may use more direct signs such as formation of the typical fracture line or the displacement of bone fragments. An analysis of the radiologic lines of interest for a physician includes their discontinuity, fragmentation, or steplike and angular deformities. Other indirect signs of damage to the orbit include thickening and induration of periorbital soft tissues caused by hemorrhage and reactive edema, subcutaneous or orbital emphysema, blood in the sinuses, induration of the soft tissue under the roof of the maxillary sinus, and pneumocephalus (Fig. 2.8) [3, 4].
Fig. 2.8
Blow-out fracture of the inferior orbital wall: the arrows indicate the orbital soft tissues prolapsed into the maxillary sinus
Unfortunately, often times numerous labor-consuming X-ray examinations of the orbit fail to give useful information [5], thus leading to misinterpretation and increase of time before the proper diagnosis is made [6, 7]. The probability of a fracture not being detected by X-ray imaging and subsequently diagnosed using coronal computed tomography is 10–13 % for the inferior wall fractures and 20–50 % for the medial wall fractures [4, 8]. Hence, diagnostic X-ray imaging is currently used for examination of the skull and the orbit only as a screening method [6, 9–11].
The final diagnosis and formation of a treatment plan should be based on the results of computed tomography (CT), which is regarded as the gold standard of radiological diagnosis of orbital fractures [12–14]. Modern equipment is capable of scanning the head structures within several seconds and producing high-resolution images, while the radiation exposure of patients remains minimal.
CT indications include suspected head injury and damage to the facial soft tissues [15].
CT scanning is typically started with examining the head with 2–3 mm table feed for assessing the base of the skull and 8 mm table feed for analyzing the supratentorial structures [16, 17]. The extent of the examination goes from the base of the cerebrum to the bregma. The plane of the slices is parallel to the plane running along the orbitomeatal line, which is conventionally used for brain examination.
Assessment of the maxillofacial region is performed in the scanning area parallel to the plane of the hard palate with a 1–2 mm slice thickness. The examined area includes the zone from the floor of the oral cavity to the end of the frontal sinuses. When the condition of the horizontal bony structures and the ostiomeatal complex needs to be assessed, CT scanning is performed again in the coronal view.
Targeted CT scanning of the orbit is necessary for the detection of periorbital edema or an orbital wall fracture.
Examination in at least two planes, the axial (horizontal) and coronal (frontal), with slice thickness less than 3 mm is used to ensure the optimal imaging of the orbit.
The axial slices are oriented parallel to the physiological horizontal line. This line which connects the infraorbital margin to the external auditory foramen and diverges 10° from the orbitomeatal line and to the optic nerve. This plane can be used to assess the orbit’s condition but cannot show the damage to the inferior and superior orbital walls [18]. Coronal CT scanning is required to search for damage to those walls and subsequently assess them [19, 20].
During coronal CT examination, a patient lies prone with his chin resting on the elevated head support so that his head was tilted back as much as possible. If necessary, the maximum extension of the cervical spine is supplemented with the negative tilt angle of a scanning device. The slices are made from the orbital opening toward its apex.
The coronal (frontal) CT scans are most informative when analyzing the condition of all four orbital walls [21, 22]. Supplementation of the coronal projection with oblique sagittal reconstructions makes it simpler to assess the length of the fracture, the volume of tissues displaced to the maxillary sinus or the ethmoidal labyrinth, and the degree of entrapment of extraocular muscles in a bone defect [23–25].
The following conditions can impede obtaining coronal images: a critical condition of a patient, endotracheal intubation (the image of the tube overlaps the contour of the orbit), or a neck injury that impedes its hyperextension. Multispiral computed tomography is used in these cases as it has a high scanning rate and can generate 3D and multiplanar reconstructions [26, 27]. Furthermore, there is no need for neck hyperextension to obtain coronal cross sections of the orbit.
The proven advantages of CT scanning are many. These include its versatility and high accuracy, the possibility of rapid assessment of the condition of several anatomic regions during the same study (such as the head, abdomen, pelvis, and spine), and clear imaging of small-scale and combined fractures which can include several orbital walls. CT scanning is also highly useful when there are many bone fragments and can help identify metal or low-contrast ferromagnetic foreign bodies that may be present in the orbit. Furthermore, CT scanning can be used to diagnose trauma complications, such as retrobulbar or subperiosteal hematoma, hemorrhage to the subsheath space of the optic nerve and the inferior rectus and inferior oblique, and orbital cellulitis and abscess. CT scanning also has relatively low cost, and allows access for emergency resuscitation if necessary,
A significant drawback of CT scanning is the radiation exposure of the crystalline lens [28, 29] if multiple repeat scans are performed. Moreover, the position of a graft covering a bony defect with respect to extraocular muscles and orbital fat sometimes cannot be properly assessed compared to the preoperative control CT scans.
Magnetic resonance imaging (MRI) of the orbits provides T1-, T2-, and proton density-weighted images in three mutually perpendicular planes using various software programs.
Magnetic resonance imaging plays a secondary role in the evaluation of orbital fractures for many diverse reasons [10–12]. MRI is not good for the imaging of bone fragments and cannot be used if there are ferromagnetic foreign bodies whose displacement and/or heating may cause severe secondary injury1. Also, MRI imaging is a long scanning procedure (up to 1 h) during which a patient needs to remain motionless, and it has a high cost (2–3 times as expensive as CT scanning) [30, 31]. There are numerous non-facial contraindications limiting the use of MRI to diagnose orbital traumas: presence of a pacemaker, metal implants, permanent makeup and tattoos (which may create artifacts and impede interpretation of the images), claustrophobia, involuntary motions of a patient during the examination, and the lack of access for emergency resuscitation equipment for life support if the need should arise [30–33].
Meanwhile, the undisputable advantages of MRI include good imaging of soft tissues, the absence of radiation exposure, and the possibility of obtaining images in all possible (axial, coronal, sagittal, and oblique) views without changing the position of the patient’s body [34].
Taking into account the aforementioned facts, nuclear magnetic resonance is used to estimate the position of an implant in the orbit and possible residual entrapment of a muscle or adipose tissue in the fracture area [28, 29], to diagnose traumatic carotid–cavernous fistula, to search for nonmetal foreign bodies, to analyze fluid accumulation in the orbit and subperiosteal space and the dynamics of conversion of methemoglobin to hemosiderin (evolution of orbital hematoma), etc. Furthermore, MRI is a useful method for assessing the condition of the orbital apex, the parasellar region, and structures of the posterior cranial fossa and the portion of the optic nerve located inside the canal and the skull [30, 31, 33, 35, 36].
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