Noortje I. Regensburg

A New and Validated CT-Based Method for the Calculation of Orbital Soft Tissue Volumes

PURPOSE There is no consensus as how to calculate orbital soft tissue volume based on CT or MRI scans. The authors sought to validate their technique and to assess the intraobserver and interobserver variability of their calculations of bony orbital volume (OV), orbital fat volume (FV), and extraocular muscle volume (MV) on CT scans of humans. METHODS The authors calculated these volumes with the use of a manual segmentation technique on CT scans with commercially available software. Two observers (one of them masked) calculated the orbital soft tissue volumes in a CT scan of a phantom constructed of dry skull, butter, and chicken muscle. These calculations were compared with previously taken standard volume measurements of these materials. Repetitive calculations on one CT scan by the same observer were compared. Soft tissue volumes taken from 10 orbital CT scans were calculated by two observers and compared. From the data acquired, intraobserver and interobserver variability was calculated. RESULTS Outcomes of these calculations using this software approximated the volumes of the phantom measured with standardized techniques. Accuracy of the phantom calculations between the two observers varied from +0.7% to -0.7% for FV and between -1.5% and -2.2% for MV. Mean differences between the repeated calculations were smaller than 5%. The intraclass correlation coefficient varied from 0.961 to 0.999. CONCLUSIONS Calculating orbital soft tissue volume using a manual segmentation technique for CT scans is a reliable and accurate tool.

Age and gender-specific reference values of orbital fat and muscle volumes in Caucasians

Aim To provide age and gender-specific reference values for orbital fat and muscle volumes (MV) in Caucasian adults. Patients and Methods Computed tomographic scans of 160 orbits from 52 men and 55 women, aged 20–80 years, not affected by orbital disease were evaluated. Orbital bony cavity volume (OV), fat volume (FV) and MV were calculated by a previously validated method using the software program Mimics. Ratios of FV to OV and of MV to OV were determined. Results OV, FV and MV were all significantly larger in men than in women (p<0.001), but FV/OV and MV/OV were similar in both sexes. OV and MV did not change with age, but FV increased with advancing age in both women (p<0.001) and men (p<0.001). Linear regression analysis with FV/OV and MV/OV ratios as dependent variables and age and gender as independent variables showed a significant correlation between age and FV/OV (r=0.52, p<0.0001) and age and MV/OV (r=−0.26, p=0.001). Conclusions Advancing age is associated with an increase of FV/OV and a minor decrease of MV/OV. Gender-specific differences in orbital FV and MV disappear once FV and MV are related to OV, by calculating the ratios FV/OV and MV/OV. Age-specific gender-neutral reference ranges (2.5 and 97.5 percentiles) of FV/OV and MV/OV are presented.

Densities of orbital fat and extraocular muscles in graves orbitopathy patients and controls.

Purpose: To investigate CT densities of orbital soft tissue volumes in patients with Graves orbitopathy (GO) and to compare these with the densities of controls. Methods: Observational case series. Of 95 patients with GO and 150 controls, soft tissue volumes, mean densities, and ratios of fat volume to orbital volume and muscle volume to orbital volume were calculated with software. The 95% confidence intervals of the controls were used as reference values. The densities were plotted against age and volume ratios. For statistical analysis SPSS 16.00.2 was used. p values were calculated with the following tests: analysis of variance, Pearson correlation, Kruskal-Wallis, Mann-Whitney, and linear regression. Results: The main outcome measurements were differences in orbital soft tissue densities. In GO patients the mean orbital fat density was significantly higher than in controls (p ≤ 0.001) and independent of age (p = 0.23). The mean extraocular muscle density of GO patients was within the range of controls and did not decrease with age (p = 0.16) as it did in controls (p ≤ 0.001). Mean fat density increased with decreasing fat volume (p = 0.001). Mean extraocular muscle density increased slightly with increasing muscle volume (p = 0.09). Muscle density correlated with fat density in both controls and GO patients. Conclusions: Orbital fat density in GO patients is significantly higher than in controls and negatively correlated to fat volume but positively correlated to muscle volume and muscle density.

Traumatic neuroma of the infraorbital nerve subsequent to inferomedial orbital decompression for Graves’ orbitopathy

Purpose. To present and discuss the occurrence of a traumatic neuroma subsequent to inferomedial orbital decompression surgery in Graves’ orbitopathy. Methods. Case report. Results. Approximately 1 month after surgery, a patient who underwent bilateral rehabilitative inferomedial orbital decompression developed a mass with clinical and radiologic characteristics compatible with a traumatic neuroma of the left infraorbital nerve. The lesion, which was thought to be the result of unnoticed nerve trauma at the time of surgical dissection of the infraorbital canal, remained stable in shape and other imaging characteristics during the 39-month follow-up period. Symptoms of trigeminal neuralgia could be only partially controlled with medical therapy (oral pregabalin 75 mg 3 times daily). Conclusions. The second branch of the trigeminal nerve may be damaged in the course of orbital floor removal decompression for Graves’ orbitopathy. This may potentially induce the formation of traumatic or amputation neuromas. Such lesions should be included in the potential complications of decompressions when counseling patients about to undergo this type of surgery, as they are difficult to treat and may cause persistent and disabling pain.