Review of orbital imaging

ACR Appropriateness Criteria® Orbital Imaging and Vision Loss-Child

Orbital disorders in children consist of varied pathologies affecting the orbits, orbital contents, visual pathway, and innervation of the extraocular or intraocular muscles. The underlying etiology of these disorders may be traumatic or nontraumatic. Presumed location of the lesion along with the additional findings, such as eye pain, swelling, exophthalmos/enophthalmos, erythema, conjunctival vascular dilatation, intraocular pressure, etc, help in determining if imaging is needed, modality of choice, and extent of coverage (orbits and/or head). Occasionally, clinical signs and symptoms may be nonspecific, and, in these cases, diagnostic imaging studies play a key role in depicting the nature and extent of the injury or disease. In this document, various clinical scenarios are discussed by which a child may present with an orbital or vision abnormality. Imaging studies that might be most appropriate (based on the best available evidence or expert consensus) in these clinical scenarios are also discussed. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Radiopathological Correlation in Orbital Lesions

PURPOSE

The objective is to analyze the radiological diagnosis of orbital lesions and their correlation with the final histopathological findings. We compared the initial reports by extramural radiologists and an in-house radiologist specialized in orbital imaging to evaluate the diagnostic accuracy in the interpretation of orbital imaging.

METHODS

This was a retrospective chart review of forty patients referred to a Tertiary Eye Care Center in South India over a period of 7 years. These patients already had their imaging done elsewhere. The imaging was re-evaluated by an in-house radiologist. The radiological findings were correlated with the histopathological diagnosis. The diagnostic accuracy between the two radiologists was compared. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value in differentiating malignant from benign lesions were calculated in both groups. The sensitivity and PPV of the radiological diagnosis for neoplastic and inflammatory lesions in both groups were analyzed.

RESULTS

The accuracy in differentiating malignant from benign and inflammatory lesions by our in-house radiologist and extramural radiologists was 95% (κ = 0.9 [0.764, 0.997]) and 50% (κ = 0.036 [-0.160, 0.232]), respectively. The sensitivity and PPV of the radiological diagnosis by our in-house radiologist were 93.31% and 100% for benign lesions and 95.24% and 95.24% for malignant lesions. On the contrary, reports from the extramural radiologists showed a sensitivity and PPV of 76.92% and 66.67% for benign lesions and 14.28% and 60% for malignant lesions.

CONCLUSION

A high radiological diagnostic accuracy is possible when analyzed by radiologists experienced in orbital imaging.

Orbital Tumors-Clinical, Radiologic and Histopathologic Correlation

Orbital masses include a broad spectrum of benign and malignant entities. Often these masses are asymptomatic or show a slow growth rate, so that emergence of clinical symptoms is prolonged. In this context, cross-sectional imaging plays an elementary role in the characterization of these lesions. Aside from the characterization of the underlying entity, an evaluation of the involved compartments is possible by sufficient imaging, which also facilitates optimal treatment and surgery planning. The purpose of this review is to explore different benign and malignant orbital tumors and their typical appearance in imaging together with histopathologic findings.

Role of Quantitative Diffusion-Weighted Imaging in Differentiating Benign and Malignant Orbital Masses

Aim  To determine the role of diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) values in differentiating benign and malignant orbital masses. Materials and Methods  After obtaining institutional ethical board approval and informed consent from all patients, an observational study was done for a period of 24 months in the radiology department of a tertiary care hospital in South India. Conventional magnetic resonance imaging and DWI using a 3T scanner was done for all patients with suspected orbital mass lesion. ADC value and clinicohistopathological correlation were studied for every patient. Chi-square test was used to compare the signal characteristics of DWI and ADC maps between benign and malignant lesions. A comparison of mean ADC values for benign and malignant masses was performed using Student's t -test for independent samples. The cut-off value for ADC was obtained using the receiver operating characteristic (ROC) curve. Results  Of 44 patients with orbital lesions, 70% were benign and 30% were malignant. There was a significant difference in the mean ADC values of benign and malignant orbital masses. Using ROC curve analysis, an optimal ADC threshold of 1.26 × 10 ^-3 mm ² /s was calculated for the prediction of malignancy with 100% sensitivity, 80.65% specificity, and 86.36% accuracy (95% confidence interval: 0.872, 1.00, p < 0.0001). Two ADC thresholds were used to characterize the orbital masses with more than 90% confidence. Conclusion  Quantitative assessment of ADC is a useful noninvasive diagnostic tool for differentiating benign and malignant orbital masses. Malignant orbital lesions demonstrate significantly lower ADC values as compared with benign lesions.

Evaluation of Proptosis: A Primer

Collapse

Quantitative characterization of extraocular orbital lesions in children using diffusion-weighted imaging

BACKGROUND

Diffusion-weighted imaging (DWI) has been shown to be helpful in providing information about cellular density and also predicting the histological features of aggressive tumors. Several studies have evaluated this technique for orbital tumors. However, very few articles have focused exclusively on evaluating pediatric orbital masses and, within those, only a small number of patients were included in the study.

OBJECTIVE

This study aimed to evaluate the use of DWI and apparent diffusion coefficient (ADC) values to differentiate between benign and malignant extraocular orbital lesions in children.

MATERIALS AND METHODS

This retrospective study included 73 patients under the age of 18 seen in our hospital between October 2016 and February 2019. The extraocular orbital lesions were evaluated clinically and radiologically using DWI. The diagnosis was confirmed by either histological examination (after biopsy or surgery) or based on clinical and radiologic evaluation.

RESULTS

The malignant lesions were found to have increased diffusion restriction in comparison to the benign lesions. The ADC values of the malignant lesions were significantly lower (P<0.0001). The use of a cutoff value of 0.99×10^-3 mm²/s allowed for the differentiation of the benign lesions and malignant lesions with a sensitivity of 75% and a specificity of 100% while the cutoff point of 1.26×10^-3 mm²/s had a sensitivity of 100% and a specificity of 73%.

CONCLUSION

Measurement of ADC in extraocular orbital lesions in children may help differentiate malignant lesions from benign lesions.

Role of Quantitative Spectral CT Analysis for Differentiation of Orbital Lymphoma and Other Orbital Lymphoproliferative Disease

PURPOSE

To investigate the value of quantitative parameters from spectral computed tomography for the differentiation of orbital lymphoma from other lymphoproliferative disease, including idiopathic orbital inflammatory disease (IOID) and IgG4-related disease (IgG4-RD).

METHODS

Patients with orbital masses who underwent pre-treatment contrast-enhanced spectral CT were enrolled in this retrospective study. The subjects were divided into lymphoma and other orbital lymphoproliferative disease groups. Qualitative imaging features (margin, location, enhancement pattern, cranial nerves, soft tissue, and bone involvement) were reviewed. Quantitative parameters (iodine density and spectral attenuation curve slope) derived from spectral CT were measured.

RESULTS

Eleven patients had orbital lymphoma and 11 had other orbital lymphoproliferative diseases (idiopathic orbital inflammatory disease (IOID), n = 5; IgG4-related disease (IgG4-RD), n = 6). Qualitative analysis showed no significant difference between the two groups. There was significantly higher iodine density in orbital lymphoma (1.24 ± 0.24 mg/ml) than in IOID/IgG4-RD (0.83 ± 0.23 mg/ml; P = 0.001). An iodine density threshold of 1.0 mg/ml gave sensitivity, specificity, and accuracy of 81.8%, with an area under the curve of 0.876 (P = 0.0003). Orbital lymphoma had a significantly higher iodine spectral attenuation curve slope (2.44 ± 0.51 HU/keV) than IOID/IgG4-RD (1.66 ± 0.47 HU/keV; P = 0.001). A threshold of 1.99 HU/keV for the spectral attenuation curve slope of 40-70 keV gave sensitivity, specificity, and accuracy of 81.8%, with an area under the curve of 0.884 (P = 0.0002).

CONCLUSIONS

Quantitative spectral CT parameters can help differentiate orbital lymphoma from other orbital lymphoproliferative disease, with lymphoma having a significantly higher iodine density value and spectral attenuation curve slope than IOID/IgG4-RD.

T2 mapping in orbital masses: preliminary study on differential diagnostic ability of T2 relaxation time

Background

T2 mapping has been proven to be useful in tumor characterization. As to orbital masses, its diagnostic value needs to be investigated.

Purpose

To evaluate the usefulness of T2 mapping in orbital masses and the ability of T2 relaxation time in differentiating malignant from benign orbital masses.

Material and Methods

Forty-seven patients with solid orbital masses (33 benign and 14 malignant) who underwent T2 mapping examination for preoperative assessment were enrolled in the current study. T2 mapping was acquired using 16 TE values (range 12–192 ms; delta TE 12 ms). Mean T2 relaxation time was calculated based on the whole mass region of interest and compared between the malignant and benign groups using the unpaired t-test. Receiver operating characteristic curve analysis was adopted to calculate its diagnostic value.

Results

Malignant orbital masses showed significantly lower T2 relaxation time than benign masses (76.4 ± 13.0 ms vs. 119.1 ± 20.4 ms; P < 0.001). If setting a T2 relaxation time of 89.5 ms as the threshold value, optimal differentiating performance could be achieved (area under the curve 0.936; sensitivity 100.0%; specificity 87.9%; accuracy 91.5%; positive predictive value 77.8%; negative predictive value 100%).

Conclusion

T2 mapping and its derived T2 relaxation time could provide quantitative information and serve as a supplementary imaging marker for differentiating malignant from benign orbital masses.

An Orbital Abscess Secondary to Intraoral Impalement

Penetrating orbital trauma in the pediatric population is rare. Even more unusual is a secondary orbital infection following penetrating trauma. Here we present a highly unusual case of fulminant facial cellulitis with an orbital abscess in an otherwise healthy 3-year-old boy following a penetrating injury to the orbit from a point of entry on the gingiva-buccal sulcus, sustained during a fall while carrying a wooden lollipop stick. Examination of the retina revealed a focal injury at the inferior pole of the globe. The organisms cultured from pus sampled from the abscess and from the discharging intraoral wound revealed the same oral commensals while the MRI revealed a track in continuity with the orbital collection.

The Use of 68Ga-DOTATATE PET/CT in the Non-invasive Diagnosis of Optic Nerve Sheath Meningioma: A Case Report

We hereby report the case of a patient with optic nerve sheath meningioma (ONSM), whose diagnosis and multidisciplinary management was guided by the use of Gallium-68 (⁶⁸Ga)-labeled dodecanetetraacetic acid-tyrosine-3-octreotate (DOTATATE) positron emission tomography (PET)/computed tomography (CT) scan. We briefly review the diagnosis and management of ONSM, and review the literature on the role and current status of nuclear imaging with somatostatin receptor ligands in the non-invasive diagnosis and management of meningiomas.

Magnetic Resonance Imaging in Orbital Pathologies: A Pictorial Review

Orbital lesions form a wide range of pathologies, that create challenges in diagnosis, management, and treatment. The high-resolution soft tissue detail provided by magnetic resonance imaging (MRI) has allowed for better lesion characterization. Especially in cases where history and clinical evaluation are insufficient, MRI plays a crucial role. MRI is also important in the detection of the extent of orbital diseases. The aim of this study was to examine the MRI characteristics of common and/or rare diseases arising from or extending into the orbita to aid radiologists in the correct diagnosis of orbital lesions.

Utility of histogram analysis of ADC maps for differentiating orbital tumors

PURPOSE

We aimed to evaluate the role of histogram analysis of apparent diffusion coefficient (ADC) maps for differentiating benign and malignant orbital tumors.

METHODS

Fifty-two patients with orbital tumors were enrolled from March 2013 to November 2014. Pretreatment diffusion-weighted imaging was performed on a 3T magnetic resonance scanner with b factors of 0 and 800 s/mm2, and the corresponding ADC maps were generated. Whole-tumor regions of interest were drawn on all slices of the ADC maps to obtain histogram parameters, including ADCmean, ADCmedian, standard deviation (SD), skewness, kurtosis, quartile, ADC10, ADC25, ADC75, and ADC90. Histogram parameter differences between benign and malignant orbital tumors were compared. The diagnostic value of each significant parameter in predicting malignant tumors was established.

RESULTS

Age, ADCmean, ADCmedian, quartile, kurtosis, ADC10, ADC25, ADC75, and ADC90 parameters were significantly different between benign and malignant orbital tumor groups, while gender, location, SD, and skewness were not significantly different. The best diagnostic performance in predicting malignant orbital tumors was achieved at the threshold of ADC10=0.990 (AUC, 0.997; sensitivity, 96.2%; specificity, 100%).

CONCLUSION

Histogram analysis of ADC maps holds promise for differentiating benign and malignant orbital tumors. ADC10 has the potential to be the most significant parameter for predicting malignant orbital tumors.

Eye Globe Abnormalities on MR and CT in Adults: An Anatomical Approach

Eye globe abnormalities can be readily detected on dedicated and non-dedicated CT and MR studies. A primary understanding of the globe anatomy is key to characterising both traumatic and non-traumatic globe abnormalities. The globe consists of three primary layers: the sclera (outer), uvea (middle), and retina (inner layer). The various pathological processes involving these layers are highlighted using case examples with fundoscopic correlation where appropriate. In the emergent setting, trauma can result in hemorrhage, retinal/choroidal detachment and globe rupture. Neoplasms and inflammatory/infective processes predominantly occur in the vascular middle layer. The radiologist has an important role in primary diagnosis contributing to appropriate ophthalmology referral, thereby preventing devastating consequences such as vision loss.

Isolated schwannoma involving extraocular muscles

BACKGROUND

Progressive strabismus initially considered idiopathic may be caused by isolated schwannomas of motor nerves to extraocular muscles, detectable only on careful imaging. This study reviewed clinical experience of a referral practice in identifying schwannomas on magnetic resonance imaging (MRI).

METHODS

We reviewed 647 cases imaged for strabismus to identify presumed cranial nerve schwannomas, identified by gadodiamide-enhanced, high-resolution surface coil orbital MRI and thin-section cranial MRI. Clinical features and management were correlated with MRI.

RESULTS

Schwannomas were identified as fusiform intraneural enlargements in 8 cases: 1 affecting the trochlear nerve; 2, the abducens nerve; and 5 the oculomotor nerve. Involved muscles were atrophic. Both abducens schwannomas, 1 superior oblique, and 1 oculomotor schwannoma were subarachnoid; 3 were intraorbital, and bilateral oculomotor lesions of 1 case extended from cavernous sinus to orbit. Associated strabismus progressed for 3-17 years. Abducens schwannoma caused esotropia; trochlear schwannoma caused hypertropia and cyclotropia. Intracranial oculomotor schwannoma caused mydriasis and exotropia. Intraorbital schwannoma caused exotropia with or without hypertropia. Since lesion diameters were 3-9 mm, 6 had been previously missed on routine MRI.

CONCLUSIONS

Progressive, acquired strabismus may be caused by isolated cranial nerve schwannomas, representing about 1% of strabismus cases in this study, involving the oculomotor more than abducens nerve. Because most schwannomas are small and deep in the orbit, findings could be readily missed by routine imaging, leading to a possible diagnosis of idiopathic strabismus. Schwannomas should be suspected when extraocular muscles are atrophic, but the causative lesions themselves are identifiable only using targeted, high resolution MRI.

Sporadic Burkitt's lymphoma/acute B-cell leukaemia presenting with progressive proptosis and orbital mass in a child

Burkitt's lymphoma (BL) is an aggressive B-cell non-Hodgkin lymphoma that is found predominantly in children, with the highest incidence occurring in Africa. The sporadic form occurs in non-endemic areas and typically involves the ileo-caecum and the bowel, whereas orbital and paranasal sinus involvement is rare. Here, we present an unusual case of sporadic BL in a Caucasian male child with rapidly progressive painful proptosis of the right eye. Magnetic resonance imaging showed an oval-shaped, extraconal mass in the supero-lateral part of the right orbit that deformed and dislocated the eyeball antero-inferiorly. The patient underwent anterior orbitotomy, and a biopsy of the excised tissue revealed a starry-sky appearance characteristic of BL. Postoperative aggressive chemotherapy was initiated with a good response after one week.

Orbital Indeterminate Lesions in Adults: Combined Magnetic Resonance Morphometry and Histogram Analysis of Apparent Diffusion Coefficient Maps for Predicting Malignancy

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate the added value of histogram analysis of apparent diffusion coefficient (ADC) maps in differentiating indeterminate orbital malignant tumors from benign tumors, compared to using magnetic resonance (MR) morphological features alone.

MATERIALS AND METHODS

We retrospectively evaluated 54 patients with orbital tumors from March 2013 to February 2015. All the patients were assessed by both routine MR and diffusion-weighted imaging, and divided into benign group and malignant group. Routine MR imaging features and histogram parameters derived from ADC maps, including mean ADC (ADCmean), median ADC (ADCmedian), standard deviation, skewness, kurtosis, and 10th and 90th percentiles of ADC (ADC10 and ADC90), were compared between two groups. Univariate and multivariate logistic regression analyses were used to identify the most valuable variables in predicting malignancy. Receiver operating characteristic (ROC) curve analysis was used to determine the diagnostic value of significant variables.

RESULTS

Multivariate logistic regression analysis indicated that two or more quadrants involved, iso-intense on T2-weighted imaging (T2WI), and ADC10 were significant predictors for orbital malignancy. By using model 2 (iso-intense on T2WI + two or more quadrants involved + ADC10 < 0.990) as the criterion, higher AUC and specificity could be achieved than by using model 1 (iso-intense on T2WI + two or more quadrants involved) alone, (model 2 vs model 1; area under curve (AUC), 0.827 vs 0.793; sensitivity, 65.4% vs 69.2%; specificity, 100% vs 89.3%).

CONCLUSIONS

Iso-intense on T2WI, two or more quadrants involved, and ADC10 are risk factors for orbital malignancy. Histogram analysis of ADC map might provide added value in predicting orbital malignancy.

Orbital tumours and tumour-like lesions: exploring the armamentarium of multiparametric imaging

Although the orbit is a small anatomical space, the wide range of structures present within it are often the site of origin of various tumours and tumour-like conditions, both in adults and children. Cross-sectional imaging is mandatory for the detection, characterization, and mapping of these lesions. This review focuses on multiparametric imaging of orbital tumours. Each tumour is reviewed in relation to its clinical presentation, compartmental location, imaging characteristics, and its histological features. We herein describe orbital tumours as lesions of the globe (retinoblastoma, uveal melanoma), optic nerve sheath complex (meningioma, optic nerve glioma), conal-intraconal compartment (hemangioma), extraconal compartment (dermoid/epidermoid, lacrimal gland tumours, lymphoma, rhabdomysarcoma), and bone and sinus compartment (fibrous dysplasia). Lesions without any typical compartmental localization and those with multi-compartment involvement (veno-lymphatic malformation, plexiform neurofibroma, idiopathic orbital pseudotumour, IgG4 related disease, metastases) are also reviewed. We discuss the role of advanced imaging techniques, such as MR diffusion-weighted imaging (DWI), diffusion tensor imaging, fluoro-2-deoxy-D-glucose positron emission tomography CT (FDG-PET CT), and positron emission tomography MRI (MRI PET) as problem-solving tools in the evaluation of those orbital masses that present with non-specific morphologic imaging findings. Main messages/Teaching points • A compartment-based approach is essential for the diagnosis of orbital tumours. • CT and MRI play a key role in the work-up of orbital tumours. • DWI, PET CT, and MRI PET are complementary tools to solve diagnostic dilemmas. • Awareness of salient imaging pearls and diagnostic pitfalls avoids interpretation errors.

Methotrexate as a Corticosteroid-Sparing Agent for Thyroid Eye Disease

OBJECTIVE

Thyroid eye disease (TED) is generally treated with oral corticosteroid therapy. A steroid sparing drug could be a useful adjunct. We reviewed our experience with methotrexate as a corticosteroid sparing agent to treat TED.

METHODS

Retrospective chart review from two eye inflammation clinics. Patients with TED who were unable to discontinue prednisone therapy without disease recurrence were included.

RESULTS

14 patients who were receiving an average of 32 mg/day of prednisone were treated with methotrexate, usually 15 mg/week orally or 20 mg/week subcutaneously. Five patients discontinued therapy for a lack of benefit or intolerance. Of the 9 patients who remained on methotrexate, all were able to discontinue prednisone completely after an average duration of 7.5 months. Improved visual acuity by at least two lines on the Snellen chart was achieved by 7 of 12 patients with reduced acuity and partial improvement in ocular motility was achieved in 5 of 14 patients.

CONCLUSIONS

Methotrexate provided an effective steroid sparing effect in a subset of patients with TED.

Imaging of adult ocular and orbital pathology--a pictorial review

Orbital pathology often presents a diagnostic challenge to the reporting radiologist. The aetiology is protean, and clinical input is therefore often necessary to narrow the differential diagnosis. With this manuscript, we provide a pictorial review of adult ocular and orbital pathology.

Idiopathic orbital inflammation syndrome with retro-orbital involvement: a retrospective study of eight patients

Background

The aim of this retrospective study was to document the clinical findings and radiological features of idiopathic orbital inflammation syndrome with retro-orbital involvement.

Methods

We searched for ophthalmological patients who received orbital imaging at Zhejiang Provincial People's Hospital between October 2003 and April 2010. Seventy-three patients were diagnosed with idiopathic orbital inflammation syndrome based on clinicoradiological features, with pathological confirmation of nonspecific inflammatory conditions in 47 patients. Eight patients (11%) had MRI or CT evidence of retro-orbital involvement. All 8 patients were diagnosed with idiopathic orbital inflammation syndrome after biopsy of the orbital lesion. MR images were obtained for all 8 patients; 3 patients also had a contrast-enhanced CT scan.

Results

Seven out of 8 patients with retro-orbital involvement also had orbital apex lesions. Of the 65 patients without retro-orbital involvement, 19 had orbital apex lesions. The difference in the number of patients with orbital apex lesions between the two populations was significant (Fisher exact test P = .002). In all 8 patients with retro-orbital involvement, the inflammation spread through the superior orbital fissure. The retro-orbital lesions were isointense to grey matter on T1-weighted images, hypointense on T2-weighted images, and displayed uniform contrast enhancement; on contrast-enhanced CT scans, they were hyperdense relative to the contralateral mirror area and had radiological contours that were similar to those seen on MR images. The diffuse inflammation with marked sclerosis and hyalinization that we observed in the patients with retro-orbital involvement is consistent with the diagnosis of the sclerosing subtype of idiopathic orbital inflammation syndrome. All 8 patients also complained of mild to moderate periorbital pain (headache).

Conclusions

In patients with idiopathic orbital inflammation syndrome, it is important to perform MRI and CT scans to identify possible retro-orbital involvement. Retro-orbital involvement is more frequent when the lesion is present in the orbital apex.

Value of MR imaging in differentiation between solitary fibrous tumor and schwannoma in the orbit

BACKGROUND AND PURPOSE

Orbital SFT is a rare tumor, often misdiagnosed as orbital schwannoma preoperatively but with different prognosis and treatment. Our aim was to evaluate MR imaging features that might distinguish orbital SFT from schwannoma.

MATERIALS AND METHODS

MR imaging including DCE scanning was performed in 9 patients with SFT and 22 patients with schwannoma in the orbit confirmed by pathology. Location, shape, margin, signal intensity, homogeneity, enhancement pattern, ER, and TIC of the tumors were retrospectively evaluated.

RESULTS

There was a statistically significant difference between SFT and schwannoma in location and T2 signal intensity (P < .05). A statistically significant difference was also found regarding the enhancement pattern of the very high-signal-intensity areas shown on T2-weighted imaging and the type of TICs (P < .01).

CONCLUSIONS

MR imaging is useful in differentiating orbital SFT and schwannoma. The enhancement pattern of the very high-signal-intensity areas shown on T2-weighted imaging and the type of TICs on DCE MR imaging played an important role in differentiating orbital SFT from schwannoma.

Abnormalities of the globe

Although much has been published in the radiology literature on the multitudinous conditions affecting the bony orbit, there has been relatively little on diseases confined to the globe itself. As current cross-sectional imaging techniques evolve, the globes can be visualized in ever greater detail, facilitating the recognition of even fairly subtle disease entities in this region. Indeed, the fact that high-resolution detailed images of this area are achievable without significant time or radiation penalty when evaluating surrounding structures means that incidental disease is not infrequently encountered. As such, common disease entities in this region are of interest to the general radiologist and the diagnosis of globe disease need not be the remit of experienced observers in specialist centres. At our institutions we have recently encountered a number of cases covering a broad spectrum of diagnoses including traumatic, neoplastic, iatrogenic, inflammatory, and infective aetiologies. The purpose of this review is to briefly revise the pertinent anatomical and physiological properties of the globe and to familiarize the reader with the computed tomography (CT) and magnetic resonance imaging (MRI) appearances of a number of these disease states. The collection of abnormalities included is not intended to be exhaustive, merely representative, with the emphasis towards those more commonly encountered.

Differentiation between benign and malignant orbital tumors at 3-T diffusion MR-imaging

INTRODUCTION

To differentiate between malignant and benign orbital tumors at 3-T diffusion MR imaging.

METHODS

A retrospective study was conducted on 47 patients (34 males and 13 females aged 4-74 years) with orbital masses. They underwent echo-planar diffusion-weighted MR imaging of the orbit with b-factor of 0, 500, and 1,000 s/mm(2) at 3-T MR unit. Apparent diffusion coefficient (ADC) maps were reconstructed, and the ADC value of the orbital mass was calculated.

RESULTS

The mean ADC value of the malignant orbital tumors (0.84 ± 0.34 × 10(-3) mm(2)/s) was significantly lower (P = 0.001) than that of the benign orbital tumors (1.57 ± 0.33 × 10(-3) mm(2)/s). The selection of an ADC value of 1.15 × 10(-3) mm(2)/s as a threshold value for differentiating malignant orbital tumors from benign lesions has a sensitivity of 95%, a specificity of 91%, and an accuracy of 93%. There was a significant difference in the ADC value between well- and poorly differentiated malignancies (P = 0.005).

CONCLUSION

Apparent diffusion coefficient value at 3 T is an additional noninvasive imaging parameter that can be used for the differentiation of malignant orbital tumors from benign lesions, the characterization of some orbital tumors, as well as the grading of orbital malignancy.