CT scanning of the paranasal sinuses: axial helical CT with reconstruction in the coronal direction versus coronal helical CT

Multiplanar Reconstructed Computed Tomography Images Improves Depiction and Understanding of the Anatomy of the Frontal Sinus and Recess

Aims

The use of multiplanar reconstructed computed tomography (CT) images of frontal recess and sinuses was assessed with regard to depiction and understanding of anatomy and effect on surgical approach.

Materials and Methods

Three otorhinolaryngologists and one radiologist read CT scans of 43 patients referred for routine paranasal sinus scans. Spiral (helical) CT scans were obtained and coronal and parasagittal reconstructions were imaged. Three hundred forty-two readings were analyzed. The scans were assessed in the coronal plane and then in the parasagittal plane. The images were assessed for (i) Bent and Kuhn classification of frontal ethmoidal sinus air cells, (ii) size of frontal sinus ostium (assessed as unsure, normal, small, or large), (iii) use of parasagittal scans regarding additional understanding of the anatomy with particular reference as to how the agger nasi cell and frontal ethmoidal cells were arranged in a three-dimensional space, and (iv) if the parasagittal scan and subsequent three-dimensional picture created altered the surgical approach. The first two criteria were assessed in the coronal plane and then in the parasagittal plane.

Results

There was no statistically significant difference between the Bent and Kuhn classification of frontoethmoidal cells on coronal and reconstructed parasagittal images (t-test; p < 0.05). The parasagittal scans were significantly better than the coronal scans for identifying and assessing the size of the frontal sinus ostium (p > 0.001; chi-square test). Assuming an intraobserver change rate (repeat error) of 10% on CT scan observations, an exact binomial test was performed on S-PLUS, which showed that there was a significant (p < 0.001) proportion of observers who changed their rating after looking at the parasagittal scan. There also was significant improvement in observers’ abilities to identify and classify the size of the frontal ostium as reflected by the number of observers who changed from being unsure on the coronal scans to sure on the parasagittal scans. Observers felt that the parasagittal scans improved their three-dimensional understanding of the anatomy of the frontal recess by 58% on a 10-point Lickert scale. In 55% of these observations, the surgical plan was altered by a mean of 70.2% on a 10-point Lickert scale based on additional information obtained by viewing the parasagittal scans.

Conclusions

The three-dimensional understanding of the frontal recess is improved greatly by using both coronal and parasagittal reconstructed images as compared with coronal images alone. This had important implications on the planning of the surgery in the frontal recess.

Analysis of the Changing Patterns of Midface Fractures Using 3D Computed Tomography: An Observational Study

This article aims to analyze the changing Le Fort fracture patterns using computed tomography (CT) scans with three-dimensional (3D) reconstruction. A prospective observational study was conducted on 60 patients with midface trauma, who had reported to MS Ramaiah Group of Hospitals, Bangalore, between January 2015 and October 2016. CT scans using 1.6 mm axial, sagittal, coronal sections were taken and their 3D reconstruction was made. The images were studied and compared with the standard Le Fort lines. The deviations from the classical Le Fort lines were analyzed and recorded. A note was also made of any additional fixation that was required for these deviations. Descriptive analysis was done and the results expressed in numbers and percentages. Study revealed that the most common cause for the midface fractures was found to be road traffic accidents (81.7%) with a male preponderance (88.3%) and peak incidence in 21 to 30 years of age (40%). Among the 60 patients, 18 (30%) patients had fracture patterns similar to the ideal Le Fort lines, 4 (6.6%) had a combination of Le Fort patterns, and 38 (66.3%) patients had deviations seen from the ideal Le Fort lines. Four types of deviations were recorded, namely, D1(60%), D2(5.4%), D3(10.9%), and D4(23.6%). It was observed that D1 and D3 required additional fixation. Majority of the cases presented as a deviation from ideal Le Fort fractures. CT was a valuable tool in the assessment of these fracture patterns. Deviations, if any, could be better analyzed using the 3D reconstruction images. Proper diagnosis and detection of these deviations make the planning for fixation easier. Repetition of these deviations could propose a newer or modified classification system for Le Fort fractures.

A Clinical and Radiological Approach to the Management of Benign Mesenchymal Sinonasal Tumors

PURPOSE

Benign mesenchymal sinonasal neoplasms (BMSN) are rare and histologically heterogeneous. Differential diagnosis, appropriate management, and outcome are still a matter of debate. The aim of this study is to provide evidence for further refinement of assessment and treatment in the future.

PROCEDURES

We retrospectively reviewed data on 93 patients with neuroradiologically verified BMSN treated at our university reference center during the past 22 years.

RESULTS

The most frequent BMSN recorded in our cohort was osteoma of the frontal sinus. Only one-third of the patients affected were symptomatic at initial presentation. The 2 other common fibro-osseous tumor entities, fibrous dysplasia and ossifying fibroma, were confirmed in 12 and 6 patients, respectively. Patients with soft tissue tumor entities such as hemangioma, glomangiopericytoma, angiofibroma, and hamartoma were all symptomatic and underwent surgical resection.

CONCLUSION

Understanding and recognizing the spectrum of appearances of benign mesenchymal sinonasal tumors will improve patient assessment and clinical management. The pathognomonic neuroradiological signs of a particular tumor entity should be actively sought as the neuroradiological features may be the diagnostic clues. Computed tomography and magnetic resonance imaging play complementary roles in identifying the morphological details and locoregional staging of benign mesenchymal sinonasal tumors.

Radiation Dose to the Eyes and Parotids during CT of the Sinuses

OBJECTIVE: To measure the radiation dose to the lens and parotid during high-resolution computed tomography scan of the sinuses.

STUDY DESIGN AND SETTING: Nine cadaver heads were scanned in the axial plane by means of a fine-cut (0.75 mm) protocol. Images were then reconstructed in the coronal and sagittal planes for use with the image guidance software. Thermoluminescent dosimeters were taped over the eyes and parotids and used to measure the radiation dose absorbed by these organs.

RESULTS: Doses obtained were 29.5 mGy for the lens and around 30 mGy for the parotid.

CONCLUSION: The measured doses are lower than the reported acute thresholds of 500-2000 mGy for lens opacities and well below the threshold of 2500 mGy for damage to the parotid.

SIGNIFICANCE: These results demonstrate minimal risk from radiation through the use of high-resolution computed tomography and support the use of such a protocol for diagnosis and preoperative planning.

Optimized imaging of the midface and orbits

A variety of imaging techniques are available for imaging the midface and orbits. This review article describes the different imaging techniques based on the recent literature and discusses their impact on clinical routine imaging. Imaging protocols are presented for different diseases and the different imaging modalities.

Diagnostic imaging modalities in head and neck disease

BACKGROUND

Because of the complex anatomy of the head and neck region, conventional projection radiography alone is unreliable and carries a high risk of misdiagnosis. The poor risk-benefit ratio of conventional radiography has led to their replacement by tomographic imaging for nearly all studies in this region.

METHOD

This review is based on pertinent articles retrieved by a selective search in the PubMed database (January 1980 to May 2013) as well as on the relevant guidelines from Germany and abroad.

RESULTS

The indication for diagnostic imaging in the anatomically complex head and neck region should be established for a specific type of imaging study on the basis of a thorough clinical examination. Conventional films, though easy to obtain, often cannot answer the diagnostic question and may yield confusing information leading to misdiagnosis. Computed tomography (CT) has the best risk-benefit profile and a high diagnostic value, but low-dose protocols have not yet been put into use in all centers. Magnetic resonance imaging (MRI) is best for bone and soft-tissue diagnosis, but consumes more resources. Digital volume tomography (DVT) is another type of three-dimensional, sectional imaging with high local resolution; the associated radiation exposure and image quality are generally both low, but may vary depending on the apparatus used. DVT cannot be used to evaluate the soft tissues. Ultrasonography can be used to evaluate superficial structures in the head and neck region; nuclear imaging can be used to evaluate thyroid disease and cancer.

CONCLUSION

Inflammatory, traumatic, and neoplastic diseases of the head and neck are best evaluated with cross-sectional imaging (CT, MRI) in accordance with current guidelines. Conventional x-rays should, in general, only be used for dental evaluation, with rare exceptions.

Don't sue the surgeon: remineralisation of the skull base or a defect that never existed?

INTRODUCTION

Intracranial complications are recognised as rare, but serious, sequelae of endoscopic sinus surgery.

CASE REPORT

A 56-year-old woman was referred after developing meningitis following elective functional endoscopic sinus surgery. Computed tomography demonstrated a significant defect of the skull base in the right posterior ethmoid, clearly visible on both coronal and sagittal sections. Operative exploration demonstrated the skull base to be intact in the posterior ethmoid area identified on the scan, and the overlying mucosa appeared undisturbed. Scans were reviewed in the light of operative findings; coronal and sagittal images were found to be reconstructions. Directly acquired coronal computed tomography, undertaken three weeks after surgery, demonstrated a complete bony plate in the right posterior ethmoid at the site previously identified as dehiscent.

DISCUSSION AND CONCLUSION

We speculate that the posterior ethmoid defect was actually an artefact of reconstruction. We cannot exclude the alternative possibility of remineralisation, but given the time frame this seems unlikely. This case highlights the need for caution when interpreting reconstructed images of the thin bony plates of the skull base and lamina papyracea, as regards both clinical significance and medicolegal reporting. While virtual defects have been reported in the superior semicircular canals as a result of reconstructed images, we believe this to be the first reported case demonstrating a similar problem in the anterior skull base.

Identification of the anterior ethmoid arteries on thin-section axial images and coronal reformatted orbit images by means of multidetector row CT

AIM

The aim of this study was to identify anterior ethmoid arteries on thin-section axial images and coronal reformatted images of the orbits using multidetector row computed tomography (CT).

MATERIALS AND METHODS

One hundred and thirty-two patients underwent paranasal CT using a 16-row detector CT (n=59) or a 6-row detector CT machine (n=73) at 1 or 1.25 mm section width, respectively. Coronal images were reformatted at section widths of 3 and 1 mm. The anterior ethmoid arteries were identified for each patient. Differences were assessed using the chi-square test.

RESULTS

All CT images were of approximately average diagnostic quality. Anterior ethmoid arteries were identified in 97.5 and 96.6% at section thicknesses of 1 and 1.25 mm on the axial images, respectively. There was no statistically significant difference in the detection rate (p=0.89). On the coronal images, anterior ethmoid arteries were presented tangentially in 75.4 and 90.2% at section widths of 3 and 1 mm, respectively. The visibility of the anterior ethmoid arteries was rated significantly better on coronal images at a section width of 1 mm than on those at section widths of 3 mm (p<0.001).

CONCLUSION

Thin-section axial images and coronal reformatted images using multi-detector row CT mostly depict anterior ethmoid arteries, and are useful to identify anterior ethmoid arteries for preoperative evaluation of paranasal sinuses.

Dose classification scheme for computed tomography of the paranasal sinuses

PURPOSE

The purpose of this study was to define objective and reproducible standards for the quality of CT images as a function of radiation doses and therapeutic validity.

MATERIALS AND METHODS

CT images of the paranasal sinuses of 145 patients (77 female, 68 male; 5-83 years old; mean age, 39.9 years) were classified both subjectively (with a view toward their validity for the planning of functional endoscopic sinus surgery, FESS) and objectively by defining the pixel noise (the standard deviation, STD, of the CT number) in a homogeneous region of interest (ROI), centered on the M. masseter and on the frontal lobe. These measurements were then compared to measurements obtained from scan images of a water-filled Perspex phantom.

RESULTS

The pixel noise measured in the phantom images was nearly identical to the respective values on the M. masseter on the patient images. The use of an edge-enhancing reconstruction algorithm and low-dose protocols, with a pixel noise amounting to 70-90 Hounsfield Units (HU), are indicated for children, chronic sinusitis, and septum deviation, while standard protocols, with a pixel noise of 50-70 HU, are recommended for the preoperative planning and postoperative control of FESS. The pixel noise for high-dose protocols is less than 50 HU; nonetheless, such protocols should generally be avoided.

CONCLUSION

The pixel noise measured in a water-filled Perspex phantom is indicative of the clinical potential and image quality of paranasal sinus CT scans. Alternatively, the M. masseter can be chosen as an ROI to measure the pixel noise in order to obtain a rough estimate of the image quality or radiation dose class.

Preoperative imaging of chronic sinusitis by multislice computed tomography

The aim of this study was to evaluate whether multislice CT enables quality improvement and dose reduction in the imaging of the paranasal sinuses, especially when using secondary reconstructions. We compared the imaging quality of direct CT scans and secondary reconstructions of single-slice CT (SSCT) as a criterion standard with multislice CT (MSCT) of the paranasal sinuses in 80 patients suspected of having chronic sinusitis. Coronary secondary reconstructions were calculated from all transversal CT data sets. Coronary reconstructions of transversal MSCT showed a significantly better image quality compared with coronary reconstructions of SSCT. Because of the absence of dental metal artifacts, coronary reconstructions of MSCT were superior even to direct coronary images of SSCT. MSCT offered a superior examination quality compared to SSCT. A halving of radiation dosage can be reached by eliminating one examination plane.

Radiation dose to the lens of eye and thyroid gland in paranasal sinus multislice CT

CT has become an established examination in the evaluation of the paranasal sinuses. Until recently this was achieved by the direct coronal technique on conventional and single slice helical scanners. With the advent of multislice technology, thin slice axial CT with excellent coronal and sagittal reconstructions is now the norm. We describe a study designed to evaluate the radiation dose to the lens of the eye and thyroid gland in the axial and coronal planes on a Siemens Volume Zoom quad slice scanner at 140 kV and effective mAs of 100 using 1 mm collimation. Thermoluminescent dosimeters were placed on the eyelid and thyroid gland of 29 patients scanned axially in the supine position and a further 28 patients scanned coronally in the prone position with gantry tilt. The results show mean doses of 35.1 mGy (lens) and 2.9 mGy (thyroid gland) in the coronal plane compared with 24.5 mGy (lens) and 1.4 mGy (thyroid gland) in the axial plane. Results obtained from a head phantom and from using the ImPACT CT dose calculator were comparable. The kV and mAs were then reduced to 120 and 40, respectively, and the axial study repeated using the head phantom and predicted doses using the ImPACT CT dose calculator. The low dose scanning technique revealed a lens dose of 9.2 mGy and thyroid dose of 0.4 mGy. The eye dose on a multislice scanner is still substantially less than the threshold dose of 0.5-2 Gy for detectable lens opacities. These results indicate that, in addition to the established perceived advantages of multislice axial sinus CT, i.e. patient comfort, no artefact from dental amalgam and reproducible true coronal images, should be included a decreased radiation dose to both the eye lens and thyroid gland compared with direct coronal scanning.

Helical CT of the local spread of carcinoma of the gallbladder: evaluation according to the TNM system in patients who underwent surgical resection

OBJECTIVE

Our aim was to evaluate the performance of helical CT as an aid in the preoperative diagnosis of the spread of carcinomas of the gallbladder.

MATERIALS AND METHODS

Two radiologists retrospectively reviewed both hard-copy and soft-copy (on a monitor with multiplanar reconstruction capability) versions of helical CT scans (3-mm collimation and 3-mm reconstruction) of 21 patients who had undergone surgical resection for carcinomas of the gallbladder. The local spread of the disease was evaluated according to the TNM system, and the results were correlated to the pathologic findings. Inter- and intraobserver differences were checked with kappa statistics. Results of the consensus interpretations were used to calculate sensitivity, specificity, and accuracy of helical CT.

RESULTS

No significant inter- or intraobserver differences were found in any T category evaluation. The sensitivities of the hard-copy consensus interpretations in the diagnosis of T1, T2, T3, and T4 lesions were 33%, 64%, 80%, and 100%, respectively; specificities of hard-copy interpretations were 94%, 80%, 81%, and 95%, respectively. For soft-copy (monitor) consensus interpretations, the sensitivities for the diagnosis of T1, T2, T3, and T4 lesions were 33%, 73%, 80%, and 100%, respectively; the specificities of soft-copy interpretations were 94%, 80%, 88%, and 95%, respectively. Overall accuracy of the hard-copy interpretation was 83%; the overall accuracy of the soft-copy interpretation was not significantly different-86%.

CONCLUSION

Helical CT provided 83-86% accuracy in the diagnosis of the local extent of carcinomas of the gallbladder, showing acceptable sensitivity and specificity for the T2 and more advanced lesions but poor sensitivity for the T1 lesions. Use of a monitor with multiplanar reconstructions of the CT data did not significantly improve the diagnostic accuracy.

Clinical applications of 2D and 3D CT imaging of the airways--a review

Hardware and software evolution has broadened the possibilities of 2D and 3D reformatting of spiral CT and MR data set. In the study of the thorax, intrinsic benefits of volumetric CT scanning and better quality of reconstructed images offer us the possibility to apply additional rendering techniques to everyday clinical practice. Considering the large number and redundancy of possible post-processing imaging techniques that we can apply to raw CT sections data, it is necessary to precisely set a well-defined number of clinical applications of each of them, by careful evaluation of their benefits and possible pitfalls in each clinical setting. In diagnostic evaluation of pathological processes affecting the airways, a huge number of thin sections is necessary for detailed appraisal and has to be evaluated, and information must then be transferred to referring clinicians. By additional rendering it is possible to make image evaluation and data transfer easier, faster, and more effective. In the study of central airways, additional rendering can be of interest for precise evaluation of the length, morphology, and degree of stenoses. It may help in depicting exactly the locoregional extent of central tumours by better display of relations with bronchovascular interfaces and can increase CT/bronchoscopy sinergy. It may allow closer radiotherapy planning and better depiction of air collections, and, finally, it could ease panoramic evaluation of the results of dynamic or functional studies, that are made possible by increased speed of spiral scanning. When applied to the evaluation of peripheral airways, as a completion to conventional HRCT scans, High-Resolution Volumetric CT, by projection slabs applied to target areas of interest, can better depict the profusion and extension of affected bronchial segments in bronchiectasis, influence the choice of different approaches for tissue sampling by better evaluation of the relations of lung nodules with the airways, or help to detect otherwise overlooked slight pathological findings. In the exploration of the air-spaces of the head and neck, targeted multiplanar study can now be performed without additional scanning by retro-reconstructed sections from original transverse CT slices. Additional rendering can help in surgical planning, by simulation of surgical approaches, and allows better integration with functional paranasal sinuses endoscopic surgery, by endoscopic perspective rendering. Whichever application we perform, the clinical value of 2D and 3D rendering techniques lies in the possibility of overcoming perceptual difficulties and 'slice pollution', by easing more efficient data transfer without loss of information. 3D imaging should not be considered, in the large majority of cases, as a diagnostic tool: looking at reformatted images may increase diagnostic accuracy in only very few cases, but an increase in diagnostic confidence could be not negligible. The purpose of the radiologist skilled in post-processing techniques should be that of modifying patient management, by more confident diagnostic evaluation, in a small number of patients, and, in a larger number of cases, by simplifying communication with referring physicians and surgeons. We will display in detail possible clinical applications of the different 2D and 3D imaging techniques, in the study of the tracheobronchial tree, larynx, nasal cavities and paranasal sinuses by Helical CT, review relating bibliography, and briefly discuss pitfalls and perspectives of CT rendering techniques for each field.

Sagittal computerized tomography reconstruction of the lateral nasal wall for functional endoscopic sinus surgery

Coronal computerized tomography (CT) scanning is imperative in the preoperative work-up for functional endoscopic sinus surgery (FESS). This study describes additional information provided by lateral CT reconstruction with special attention to the (naso-) frontal recess. Thin axial scans were taken from 10 patients suffering from chronic rhinosinusitis. This procedure avoided artefacts from dental fillings on the computerized reconstructions. The common landmarks of the lateral nasal wall as described in the surgical anatomy of FESS were easily identified on sagittal views. The average angulation of the sagittal plane from the midline required to obtain optimal images of the frontal recess was antero-posteriorly 8.7 degrees (SD, 2.4), cranio-caudally 7.7 degrees (SD, 2.6). Size and condition of the frontal recess could be demonstrated. Variations of the angle between frontal sinus and ethmoid infundibulum appeared to depend on the anterior projection of the frontal sinus and may give an indication as to the optimal endoscopic angle for visualization of the frontal ostium. Sagittal reconstructions provide information for better spatial orientation particularly in the plane of the surgical approach and may help to diagnose underlying functional changes of chronic frontal sinusitis.

Petrosal bone: coronal reconstructions from axial spiral CT data obtained with 0.5-mm collimation can replace direct coronal sequential CT scans

PURPOSE

To investigate whether coronal multiplanar reconstruction (MPR) images of the petrosal bone from axial spiral computed tomographic (CT) data obtained with 0.5-mm collimation can replace direct coronal sequential CT scans obtained with 0.5- or 1.0-mm collimation.

MATERIALS AND METHODS

The differences in diagnostic quality between thin-section coronal sequential CT scans of 24 petrosal bones in 12 patients and matched MPR images were assessed by five observers. The matched MPR images were calculated with both trilinear and tricubic interpolation. Image resolution was determined by measuring the three-dimensional point spread function.

RESULTS

All observers preferred tricubically interpolated MPR images over trilinearly interpolated images. Subjective differences in image quality between direct coronal scans and matched tricubically interpolated MPR images were small. Only the direct coronal scans with the highest image quality (0.5-mm collimation, 465 mAs) were judged to be slightly better than the matched MPR images. With regard to direct coronal scans obtained at 245 mAs and/or 1.0-mm collimation, either there was no preference or the MPR images were preferred.

CONCLUSION

Coronal MPR images from axial spiral CT obtained with 0.5-mm collimation can replace direct coronal sequential CT scans.