Orbital magnetic resonance imaging

Vitreous deformation during eye movement

Retinal detachment results in visual loss and requires surgical treatment. The risk of retinal detachment depends, among other factors, on the vitreous rheology, which varies with age. To date, the viscoelasticity of the vitreous body has only been measured in cadaver eyes. However, the ex vivo and in vivo viscoelasticity may differ as a result of the effect of intravitreal membranes. Therefore, an MRI method and appropriate postprocessing tools were developed to determine the vitreous deformation and viscoelastic properties in the eyes of living humans. Nineteen subjects (eight women and 11 men; mean age, 33 years; age range, 14-62 years) gazed at a horizontal sinusoidal moving target during the segmented acquisition of complementary spatial modulation of magnetization images. The center of the lens and the scleral insertion of the optic nerve defined the imaging plane. The vitreous deformation was tracked with a dedicated algorithm and fitted with the commonly used viscoelastic model to determine the model parameters: the modified Womersley number a and the phase angle b. The vitreous deformation was successfully quantified in all 17 volunteers having a monophasic vitreous. The mean and standard deviation of the model parameters were determined to be 5.5 ± 1.3 for a and -2.3 ± 0.2 for b. The correlation coefficient (-0.76) between a and b was significant. At the eye movement frequency used, the mean storage and loss moduli of the vitreous were around 3 ± 1 hPa. For two subjects, the vitreous deformation was clearly polyphasic: some compartments of the vitreous were gel-like and others were liquefied. The borders of these compartments corresponded to reported intravitreal membrane patterns. Thus, the deformation of the vitreous can now be determined in situ, leaving the structure of the intravitreal membranes intact. Their effect on vitreous dynamics challenges actual vitreous viscoelastic models. The determination of the vitreous deformation will aid in the quantification of local vitreous stresses and their correlation with retinal detachment.

Variations and anomalies of the human orbital muscles

The purpose of the study is to describe some rare and hitherto unreported uni- and bilateral anomalies of the orbital rectus muscles (duplication, triplication, accessory bellies, interrectal muscular bridges, false insertion) which were found by chance during the dissections of three cadavers (one adult, two fetuses). The levator palpebrae superioris muscles in the same specimens exhibited some variations (medial and lateral muscular slips) and anomalies (bipartite and unipartite levator). Cross-sections of interrectal bridges in the orbit of an adult were investigated histologically. Numerous nerves were distributed in the interstitium; groups of lipofuscin granules were found in all the myocytes. An attempt is made to explain these anomalies and variations through consideration of developmental and comparative anatomy. The relevance of these anomalies in coronal sections such as those acquired from CT and MRI is discussed.

Bilateral supernumerary rectus muscles of the orbit

A bilateral anomaly of the rectus muscles and a unilateral variation of the levator palpebrae muscle were found in the right and left orbits of an 84-year-old man. The anomaly was in the form of a supernumerary rectus muscle lying on a sagittal orientation between the optic nerve and lateral rectus muscle (in the right orbit) and adjacent to the inferior rectus muscle (in the left orbit). In each orbit the anomalous muscle originated occipitally from the common tendinous ring and frontally-near the eyeball-joined the terminal part of the inferior rectus. On its superior margin the anomalous muscle had, in the right orbit, a broad (4 mm), and in the left orbit a slender (2 mm) muscular bridge to the superior rectus muscle. Because of their connection to the superior rectus and their innervation by N.III the accessory orbital muscles are not deemed to be vestiges of the retractor bulbi muscle which, with the exception of the primates, is a typical occurrence in vertebrates and is always innervated by N.VI. Our anomalous orbital muscle must be explained as a supernumerary rectus muscle. A further variation occurred in the right orbit: an isolated medial part or belly of the levator palpebrae muscle (the so-called M. gracillimus). In primates this variation is known as a remnant of the membrana nictitans (third eyelid of the amniotes). Ignorance of anomalies in the orbital muscles may lead to confusion and error in diagnostic identification and surgical exposure.

Indications for and accuracy of magnetic resonance imaging and computed tomography in orbital disease

All patients referred for orbital imaging to the neuroradiology department of the Institute of Neurological Sciences in Glasgow over a three year period were enrolled in the study and were scheduled to undergo both magnetic resonance imaging and computed tomography. A total of 101 of the 110 referred patients were deemed suitable for analysis. Details of key presenting symptoms, signs, and a pre-imaging diagnosis were recorded prospectively. A final diagnosis was obtained by histology in 65% of cases with an orbital abnormality, by a minimum of one year of clinical review in 19.5%, by response to antibiotic or steroid therapy in 8.5%, or by conclusive investigations such as carotid angiography in in 7% of patients, 29% of the patients had no detectable orbital disease despite a minimum one years' follow-up, and so were regarded as a "normal" group. The images were interpreted prospectively by separate masked observers. The diagnostic accuracies of the two techniques were compared to the final diagnosis. The two imaging methods were shown to be comparable in overall diagnostic accuracy, with a small and statistically non-significant advantage held by magnetic resonance imaging. Interpretation of the two investigations gave more accurate information in different types of disease.

Magnetic resonance imaging evaluation of uveal tumors

We detected seven tumors with magnetic resonance imaging, which demonstrate some of the uses and limitations of this diagnostic technique. In one patient, the correct diagnosis of extraocular extension was demonstrated with magnetic resonance imaging when both clinical and ultrasonographic data were not diagnostic. In another case, an extremely small area of extraocular extension was detected with ultrasound evaluation but was not noted on magnetic resonance imaging. Magnetic resonance imaging is highly reliable in the detection of intraocular tumors. In pigmented uveal melanomas it is both sensitive and highly specific. In amelanotic processes magnetic resonance imaging can identify a mass but cannot always adequately characterize it. Further experience will be necessary to determine the proper role of magnetic resonance imaging in the evaluation of uveal tumors.

Immunohistochemical characterization of epithelial cells in human lacrimal glands. II. Inflammatory and neoplastic lesions of lacrimal glands

The distribution of cytokeratins (CK), actin, lactoferrin (Lf), lysozyme (Ly), vimentin and S-100 protein was immunohistochemically investigated in paraffin-embedded specimens of five inflammatory and five neoplastic lesions of lacrimal glands (LGs). Atrophic acini in dacryoadenitis reacted with antibodies (ABs) KL1 and Pkk1 (CK 7, 8, 17, 18) in a manner similar to ducts. Apart from myoepithelial cells and some luminal-duct cells, the remaining epithelia in dacryoadenitis were negative with AB 34 beta E12 (CK 5). The number of AB HHF35 (actin)-positive myoepithelial cells was not altered in dacryoadenitis. Epithelia in dacryoadenitis reacted weakly but consistently with Lf while revealing weak and inconsistent staining for Ly. Vimentin was negative in epithelial cells in dacryoadenitis except in one case. S-100 protein was detected only in epithelia of inflammatory major LGs. Epimyoepithelial islands in lymphoepithelial proliferation reacted variably for CKs, Lf, Ly and vimentin and remained negative for actin and S-100. In pleomorphic adenomas, neoplastic cells showing duct-like differentiation (luminal) reacted consistently with CK 7, 8, 17, 18 and S-100 protein and inconsistently with CK 5, Lf and Ly but remained negative for actin and vimentin. Other neoplastic cells (ovoid/peripheral cells) stained consistently for CK 5, vimentin and S-100 protein and focally for CK 7, 8, 17, 18, actin, Lf and Ly. Spindle-form neoplastic cells found in the stroma exhibited vimentin and S-100 protein and, less frequently, actin. Determination of these antigens in pleomorphic LG adenomas may help to evaluate their prognosis.

Neuroimaging in neuro-ophthalmology

Computed tomographic scanning is an excellent modality for evaluation of most orbital and intracranial tumors and strokes. However, MR scanning is definitely superior to CT when evaluating for multiple sclerosis, posterior fossa lesions (evaluation of gaze palsies, internuclear ophthalmoplegia, and downbeat nystagmus), or when assessing an area where sagittal scanning is important (chiasmal lesions). Magnetic resonance has increased specificity when the CT is equivocal. Although MR and CT may be complementary in the information they provide, many clinical studies have shown MR to be superior to CT in evaluating cerebral infarctions, hematomas, the intracanalicular optic nerve, optic chiasm, sella turcica, and the cavernous sinus. Magnetic resonance generally has replaced metrizamide CT cisternography as the procedure of choice for evaluating the suprasellar cistern and posterior fossa. Computed tomography is still preferable for major trauma, especially involving acute fractures and hematomas, although MR is more sensitive to the more subtle intracerebral lesions, such as shear injuries and subdural hematomas, that may provide prognostic information. Computed tomography also is preferred in situations where detecting small amounts of calcification is important for the differential diagnosis. As the development of MR imaging continues with faster scan times, finer spatial resolution, the use of paramagnetic contrast agents, and with increased availability and decreased cost, MR imaging may become preferable to CT as the imaging modality of choice for the CNS and orbit.

Magnetic resonance imaging of the orbits using a binocular surface coil

Sixty subjects, including 12 normal volunteers, have been studied using the Aberdeen 0.08 T magnetic resonance imager. A wide range of pathological conditions, including both ocular and and orbital disease, have been examined using a specialized binocular surface coil. The images produced using this coil are superior to those made with a head coil and have the advantage of demonstrating both eyes simultaneously. Each patient has been studied using a pulse sequence combining alternate saturation-recovery and inversion-recovery pulses. The resultant short time-to-inversion inversion-recovery and saturation-recovery images have been shown to be accurate in demonstrating the normal anatomy of the globe and orbit and for the demonstration of a wide range of disease states.

Rectus muscle position in V-pattern strabismus. A study with coronal computed tomography scanning

Coronal computerized tomographic (CT) scans were obtained on ten children with previously unoperated V-pattern strabismus and ten control patients to determine the relationship of rectus muscles to the globe. All patients with V-pattern had sufficient overaction of the inferior oblique muscles to warrant bilateral surgical weakening. Control patients had no strabismus or isolated horizontal deviations without A- or V-patterns. Using a horizontal reference line constructed along the anterior cranial fossa, the mean horizontal rectus-muscle axes were found to approximate the expected value of 180 degrees closely. The vertical rectus muscle axes were excyclotorted in both groups. However, there was no significant difference in the mean superior temporal quadrant angles formed by the intersection of the horizontal and vertical rectus muscle axes. Analysis of covariance with age as the covariant demonstrated a significant relationship (P less than 0.01) between age and the superior temporal quadrant angle measured in each eye. Our data suggest that apparent rectus muscle malposition identified by CT scanning is a function of age and cannot be implicated as an important cause of V-pattern strabismus.

Orbital dermoid cyst

Over a thirteen year period forty patients underwent surgery to remove an orbital dermoid cyst. Cysts which became manifest after the age of three years were deeper and larger than most that were noted before that age. Three out of four epidermoid cysts appeared after the age of 17 years and had an intracranial component. The majority of cysts showed histological evidence of leakage and associated inflammation. It is our view that dermoid cysts should be totally excised because they gradually enlarge and cause inflammation and scarring in adjacent structures.

Diagnosis of orbital myositis by nuclear magnetic resonance imaging

Two cases of orbital myositis are reported in which precise identification of the involved muscle was possible with the use of surface coil nuclear magnetic resonance (NMR) imaging. A clinical response to oral steroids in both cases coincided with a marked reduction in the abnormal thickening of the muscles as seen on the NMR images.

Nuclear magnetic resonance imaging of subretinal fluid

We ascertained the relationship between the relaxation time of magnetic resonance imaging and the protein concentration of subretinal fluid, by examining rhegmatogenous and nonrhegmatogenous retinal detachments with a 0.15 tesla nuclear magnetic resonance system, and we calculated T1 and T2 relaxation times of subretinal fluid. The protein concentration of subretinal fluid obtained at the time of surgery was determined by a biochemical method. The subretinal fluid in a fresh rhegmatogenous retinal detachment had a low protein concentration and relaxation times equal to those of vitreous. Conversely, increased protein concentrations and shortened relaxation times were noted in subretinal fluid from long-standing rhegmatogenous retinal detachments. Subretinal fluid in a nonrhegmatogenous retinal detachment with a high concentration of protein showed much shorter relaxation times. The relaxation times and protein concentration of the subretinal fluid correlated closely. It may be possible to measure the protein concentration of subretinal fluid in vivo with nuclear magnetic resonance imaging.