Neuronavigation in endoscopic skull base surgery and the accuracy of different MRI sequences.

OBJECTIVE: Neuronavigation is common technology used by skull base teams when performing endoscopic endonasal surgery. A common practice of MRI imagining is to obtain 3D isotopic gadolinium enhanced T1W magnetisation prepared rapid gradient echo (MPRAGE) sequences. These are prone to distortion when undertaken on 3 T magnets. The aim of this project is to compare the in vivo accuracy of MRI sequences between current and new high resolution 3D sequences. The goal is to determine if geometric distortion significantly affects neuronavigation accuracy. METHODS: Patients were scanned with a 3D T1 MPRAGE sequence, 3D T1 SPACE sequence and a CT stereotactic localisation. Following general anaesthesia, patients were registered on the Stealth Station (Medtronic, USA) using a side mount emitter for Electromagnetic navigation. A variety of surgically relevant anatomical landmarks in the sagittal and coronal plane were selected with real and virtual data points measured. RESULTS: A total of 10 patients agreed be enrolled in the study with datapoints collected during surgery. The distance between real and virtual datapoints trended to be lower in SPACE sequences compared to MPRAGE. Paired t test did not demonstrate a significant difference. CONCLUSION: We have demonstrated that navigational accuracy is not significantly affected by the type of MRI sequence selected and that current corrective algorithms are sufficient. Navigational accuracy is affected by many factors, with registration error likely playing the most significant role. Further research involving real time imaging such as endoscopic ultrasound may hopefully address this potential error.

Magnetic Resonance Imaging of Idiopathic Orbital Myositis.

PURPOSE: To characterize the qualitative and quantitative features of idiopathic orbital myositis (IOM) on MRI. METHODS: This was a multicenter retrospective study of patients with active IOM with MRI. Patients with incomplete clinical records, poor-quality or interval scans without active myositis, and specific orbital myositis (i.e., orbital myositis secondary to an identified condition) were excluded. An enlargement ratio was calculated by dividing the diameters of the affected extraocular muscle (EOM) by the contralateral unaffected EOM. RESULTS: Twenty-four patients (mean age: 44.4 ± 17.8 years-old, male: 11) between 2011 and 2022 were included. One case (4.2%) was pediatric (17 years old), and 6 cases presented with recurrence. Active IOM was characterized by fusiform EOM enlargement, high T2 signal, and contrast enhancement. Average maximal EOM diameters ranged from 4.6 to 7.7 mm (enlargement ratio: 1.4-2.2). Eighteen (75%) patients had single EOM involvement, most commonly the medial rectus. Other ipsilateral structures affected included focal orbital fat (16/24, 66.7%) and lacrimal gland (8/24, 33.3%). Contralateral changes in the EOM and/or lacrimal gland were observed in 7 patients (29.2%). Patients presenting with recurrence were likely to develop ongoing recurrent episodes (p = 0.003). CONCLUSIONS: Various radiological patterns of involvement described including EOM enlargement, contrast enhancement, abnormal signal, and involvement of other orbital structures are indicative of active IOM. IOM remains a heterogeneous spectrum of acute and chronic clinico-radiological presentations. Inflammation may involve other ipsilateral or contralateral orbital structures or may be bilateral despite presenting clinically as unilateral disease. Quantitative measurements may have utility in differentiating IOM from other causes of orbital myositis.

Plexiform Schwannoma of the Eyelid.

Plexiform schwannoma of the lacrimal gland of the palpebral lobe has not been previously described. This 41-year-old male presented with a 2-year history of a left upper eyelid mass and associated regional irritation. MRI of the head and orbits confirmed a left superolateral multinodular mass centered on the palpebral lobe of the left lacrimal gland. Excision revealed a schwannoma of the plexiform subtype.

Cutaneous squamous cell carcinoma radiographically mimicking infiltration into the lacrimal gland.

Cutaneous squamous cell carcinoma (SCC) is a common malignancy of the skin, with the potential for local invasion and metastasis. Here, we present a case series of two patients with SCCs, suggesting radiological infiltration of the lacrimal gland on magnetic resonance imaging. However, histopathological examination revealed lymphoplasmacytic infiltration of the lacrimal gland consistent with dacryoadenitis, with no evidence of SCC infiltration. Our cases highlight the potential for peritumoural inflammation to cause dacryoadenitis and radiologically mimic tumour infiltration into the lacrimal gland.

Orbital Artifacts on MRI.

PURPOSE: To describe artifacts on orbital MRI, which led to an incorrect radiology report. METHODS: Retrospective chart review of patients identified from the orbital databases at the Royal Adelaide Hospital and University of Wisconsin Hospital. Patients who had artifacts on orbital MRI that led to an incorrect radiology report were included. Records were evaluated for age at imaging, gender, MRI sequence, laterality, and location of artifact, radiological characteristics and misdiagnosis, and cause of artifact. RESULTS: Data were collected from 7 patients (3 male) who had a median age of 61 years at the time of imaging. Five artifacts resulted from fat-suppression failure with 4 of these cases misdiagnosed as inflammatory changes and 1 misdiagnosed as neoplastic infiltration. The OD was involved in 4 cases. Six cases were in the inferior orbit region. CONCLUSIONS: Fat-suppression failure artifacts may arise in the inferior orbit region and can be mistaken for inflammatory or neoplastic orbital disease. This may prompt additional investigations such as orbital biopsy. Clinicians should be aware of artifacts which can affect orbital MRI and lead to potential misdiagnosis.

Case Report: Late spontaneous orbital subperiosteal hematoma after endoscopic sinonasal tumor resection.

INTRODUCTION AND IMPORTANCE: We report a case of spontaneous subperiosteal orbital hematoma many years after endoscopic sinonasal resection of malignancy. CASE PRESENTATION: A 50-year-old female with a six-year history of endoscopic sinonasal resection of a poorly differentiated neuroendocrine tumor presented with two days of worsening frontal headache and left periocular swelling. A subperiosteal abscess was initially suspected on CT; however, MRI sequences revealed changes consistent with the diagnosis of hematoma. A conservative approach was justified based on the clinico-radiologic features. Progressive clinical resolution was noted over three weeks. Two monthly follow-up MRI revealed resolution of the orbital findings with no features to indicate recurrence of malignancy. CLINICAL DISCUSSION: Subperiosteal pathologies can be clinically challenging to differentiate. Differing radiodensities on CT may help differentiate between them but is not always reliable. MRI is more sensitive and is the preferred imaging modality. CONCLUSION: Spontaneous orbital hematomas are self-resolving, and surgical exploration may be avoided in the absence of complications. Therefore, it is beneficial to recognize it as a potential late complication of extensive endoscopic endonasal surgery. Characteristic features on MRI can aid diagnosis.

Disseminated thrombosis of the internal jugular vein, superior ophthalmic vein and cavernous sinus as the primary manifestation of occult malignancy: a case report.

Internal jugular vein (IJV) thrombosis is a life-threatening condition most often associated with local risk factors such as head or neck infection or central venous catheterisation. Underlying malignancy is a rare but important aetiology to consider in patients presenting with spontaneous IJV thrombosis. We describe a case of necrotic cervical lymphadenopathy with thrombosis of the IJVs, cavernous sinuses and superior ophthalmic veins in a patient with metastatic squamous cell carcinoma, which was further complicated by an orbital compartment syndrome. The differential diagnosis of IJV thrombosis includes a range of infective, metastatic and thrombophilic pathologies. This case illustrates that, in the absence of an underlying precipitating factor, spontaneous IJV thrombosis should prompt further systemic investigations. Furthermore, patients with thrombotic events affecting the orbital venous drainage system should be monitored closely for signs of an acute orbital compartment syndrome.

Synthetic cranial MRI from 3D optical surface scans using deep learning for radiation therapy treatment planning.

BACKGROUND: Optical scanning technologies are increasingly being utilised to supplement treatment workflows in radiation oncology, such as surface-guided radiotherapy or 3D printing custom bolus. One limitation of optical scanning devices is the absence of internal anatomical information of the patient being scanned. As a result, conventional radiation therapy treatment planning using this imaging modality is not feasible. Deep learning is useful for automating various manual tasks in radiation oncology, most notably, organ segmentation and treatment planning. Deep learning models have also been used to transform MRI datasets into synthetic CT datasets, facilitating the development of MRI-only radiation therapy planning. AIMS: To train a pix2pix generative adversarial network to transform 3D optical scan data into estimated MRI datasets for a given patient to provide additional anatomical data for a select few radiation therapy treatment sites. The proposed network may provide useful anatomical information for treatment planning of surface mould brachytherapy, total body irradiation, and total skin electron therapy, for example, without delivering any imaging dose. METHODS: A 2D pix2pix GAN was trained on 15,000 axial MRI slices of healthy adult brains paired with corresponding external mask slices. The model was validated on a further 5000 previously unseen external mask slices. The predictions were compared with the "ground-truth" MRI slices using the multi-scale structural similarity index (MSSI) metric. A certified neuro-radiologist was subsequently consulted to provide an independent review of the model's performance in terms of anatomical accuracy and consistency. The network was then applied to a 3D photogrammetry scan of a test subject to demonstrate the feasibility of this novel technique. RESULTS: The trained pix2pix network predicted MRI slices with a mean MSSI of 0.831 ± 0.057 for the 5000 validation images indicating that it is possible to estimate a significant proportion of a patient's gross cranial anatomy from a patient's exterior contour. When independently reviewed by a certified neuro-radiologist, the model's performance was described as "quite amazing, but there are limitations in the regions where there is wide variation within the normal population." When the trained network was applied to a 3D model of a human subject acquired using optical photogrammetry, the network could estimate the corresponding MRI volume for that subject with good qualitative accuracy. However, a ground-truth MRI baseline was not available for quantitative comparison. CONCLUSIONS: A deep learning model was developed, to transform 3D optical scan data of a patient into an estimated MRI volume, potentially increasing the usefulness of optical scanning in radiation therapy planning. This work has demonstrated that much of the human cranial anatomy can be predicted from the external shape of the head and may provide an additional source of valuable imaging data. Further research is required to investigate the feasibility of this approach for use in a clinical setting and further improve the model's accuracy.

Normative orbital measurements in an Australian cohort on computed tomography.

PURPOSE: To determine the normal diameters of the extraocular muscles (EOMs) and optic nerve sheath complex (ONSD) and correlate with patient demographics in an Australian cohort. METHODS: Consecutive patients who underwent contrast enhanced computed tomography (CT) orbits between December 2017 and March 2021 were included. Patients with bilateral disease, previous orbital surgery, or poor scan quality were excluded. Normal orbit was used in patients with unilateral orbital disease. RESULTS: Two hundred one orbits from 201 patients were included. Normal measurements (mean ± SD) were as follows: medial rectus (MR) 4.22 ± 0.56 mm; inferior rectus (IR) 4.20 ± 0.70 mm; lateral rectus (LR) 3.40 ± 0.56 mm; superior muscle group (SMG) 4.13 ± 0.72 mm; superior oblique (SO) 2.60 ± 0.43 mm; inferior oblique (IO) on quasi-sagittal plane 2.19 ± 0.42 mm, and the ONSD 5.62 ± 0.82 mm. The mean diameters of the LR, SMG, IR, SO, and ONSD were significantly larger in male than female patients (p < .05). Statistically significant correlation was found between age and the diameters of the LR (r = 0.29, p < .01), SMG (r = 0.22, p < .01), IO on a coronal plane (r = -0.18, p < .01), and ONSD (r = 0.16, p = .02). CONCLUSION: This normative data may be used to diagnose pathological enlargement of the optic nerve and extraocular muscles, including involvement of the oblique muscles.

Optic nerve infiltration in systemic non Hodgkin lymphoma.

Optic nerve infiltration secondary to systemic non-Hodgkin lymphoma (NHL) is a rare phenomenon. We present a 55-year-old man with low-grade systemic NHL who initially presented with an isolated optic neuropathy and non-specific neurological symptoms. We further present a literature review of systemic NHL with radiological evidence of optic nerve infiltration. On magnetic resonance imaging, the characteristic features include optic nerve enhancement and enlargement, while leptomeningeal enhancement is uncommon. Cerebrospinal fluid analysis and optic nerve sheath biopsy can return false negative results, and when such investigations are inconclusive, biopsy of the optic nerve substance has a high diagnostic yield. Although rare, lymphomatous optic nerve infiltration must be considered in the differential diagnosis of a pale swollen optic disc.

Radiological analysis of orbital lymphoma histological subtypes.

PURPOSE: To characterise the radiological features of orbital lymphoma subtypes. METHODS: This was a multicentre, retrospective study to analyse radiological and clinical characteristics of orbital lymphoma by histological subtype across two sites within Australia and the United States. RESULTS: A total of eighty-eight patients were included. The most common subtypes were extranodal marginal zone lymphoma [EMZL] (48, 54.5%), follicular lymphoma [FL] (16, 18.2%), and diffuse large B-cell lymphoma [DLBCL] (15, 17.0%). Clinically, significant associations were found between DLBCL and vision change (p < .01), pain (p < .01), extraocular movement limitation (p = .01), and optic neuropathy (p = .01). Radiologically, there was no significant difference between the individual histopathological sub-groups with respect to bone destruction (p = .30), optic nerve involvement (p = .30) and diffuse appearance (p = .84). However, if categorised as either aggressive or indolent, aggressive lymphoma subtypes were significantly more likely to demonstrate globe indentation radiologically than indolent subtypes (Odds Ratio = 5.5, 95% CI: 1.3, 23.3; p = .02). CONCLUSIONS: DLBCL was significantly associated with vision change, pain, extraocular movement limitation and optic neuropathy clinically. Aggressive lymphoma subtypes were significantly more likely to demonstrate globe indentation radiologically. Otherwise, there were no significant differences between lymphoma subtypes and radiological findings on MRI and CT.

Normative lacrimal gland dimensions by magnetic resonance imaging in an Australian cohort.

PURPOSE: To report the normative dimensions of the lacrimal gland on fat-suppressed contrast-enhanced magnetic resonance imaging (MRI) in an Australian cohort. METHODS: Retrospective review of patients who underwent 3 T orbital MRI is presented. Two hundred eleven orbits were used to conduct lacrimal gland measurements. Orbits were excluded if there was ipsilateral orbital or lacrimal gland disease, prior surgery, or poor image quality. The length and width of the lacrimal gland were measured in axial and coronal sections using the largest image. RESULTS: The mean lacrimal gland axial length was 14.6 mm in the right orbit and 14.3 mm in the left orbit. The mean axial width was 4.9 mm in both orbits. Coronal lengths averaged 16.2 mm in the right orbit and 16.4 mm in the left orbit. The coronal width averaged 4.8 mm in both orbits. A significant negative correlation was found between age and the right axial length (r = -0.26, p < .01) and the left axial length (r = -0.26, p < .01) of the lacrimal gland. No statistically significant difference was found between genders or laterality. CONCLUSION: This study presents the normal lacrimal gland dimensions on fat-suppressed contrast-enhanced MRI in an Australian cohort. An inverse relationship exists between age and the axial length of the lacrimal gland. These data may be used to help diagnose enlargement of the lacrimal gland.

Normative globe position values on orbital computed tomography in Australians.

OBJECTIVE: To determine normal globe position values, interzygomatic distance (IZD), and globe axial length and width on computed tomography in an Australian cohort. DESIGN: Retrospective cohort study. PARTICIPANTS: Patients who underwent computed tomography of the orbits. Patients with bilateral disease, previous orbital surgery, or poor scan quality were excluded. METHODS: An axial slice through the midglobe was used to conduct the globe position measurements. Anterior globe position was defined as the perpendicular distance from the anterior globe margin to the interzygomatic line and posterior globe position as the perpendicular distance from the posterior globe margin to the interzygomatic line. RESULTS: The normal measurements (mean ± SD) were IZD, 97.4 ± 4.1 mm; anterior globe position, 18.8 ± 2.8 mm; posterior globe position, 6.2 ± 2.9 mm; axial globe length, 24.9 ± 1.1 mm; and axial globe width, 25.9 ± 1.2 mm. A significant positive correlation was seen between the IZD and the anterior globe position (r = 0.15, p = 0.03), axial globe length (r = 0.33, p < 0.01), and axial globe width (r = 0.30, p < 0.01). CONCLUSION: This normative globe position data may be used to diagnose radiologic exophthalmos or enophthalmos.

Evaluation of orbital lesions with DCE-MRI: a literature review.

PURPOSE: To provide a major review on the applications of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in evaluating orbital lesions. This review also outlines selected scenarios where DCE-MRI may be helpful. METHODS: A comprehensive retrospective literature review of all English language publications on PubMed, EMBASE, and Google Scholar between 1994 and 2022. This literature review examined the specific applications and clinical scenarios surrounding the utility of DCE-MRI in orbital lesions and various findings that have been presented in the current literature. RESULTS: DCE-MRI provides information on tissue physiology and permeability, beyond the anatomical features displayed on static imaging. Various measured parameters (qualitative, semi-quantitative, and quantitative) obtained by DCE-MRI have been used to differentiate between benign and malignant lesions, specific orbital lymphoproliferative diseases (OLPD), lacrimal gland lesions, and various rare orbital tumours. DCE-MRI has a limited role as an initial diagnostic imaging modality. However, DCE-MRI may prove to have benefit in predicting and monitoring treatment response in orbital lymphoma as a critical imaging study, but literature specific to orbital malignancies remains limited. CONCLUSION: The value of DCE-MRI may be in situations of diagnostic uncertainty, where it may be an additional imaging aid following conventional imaging techniques. It may also act as a critical imaging modality for monitoring of orbital tumour treatment response, but the literature remains limited. Standardisation of imaging protocol, measured parameters, and statistical analysis remain limitations of this imaging technique.

Radiological Features of Bilateral Sequential Leukaemic Optic Nerve Infiltration: A Case Report.

Leukaemic infiltration of the optic nerve is an oncologic emergency that can lead to a significant risk of irreversible vision loss and has an overall poor systemic prognosis. We present the case of a 77-year-old man in previous systemic remission from acute myeloid leukaemia (AML) who developed bilateral sequential leukaemic optic nerve involvement with eventual complete vision loss. A review of the clinical and radiological characteristics of optic nerve infiltration in AML is provided. Profound vision loss to the order of 20/200 or worse is common. Magnetic resonance imaging features include optic nerve thickening, enhancement of the nerve sheath, T2 hyperintensity and restricted diffusion. Urgent orbital radiotherapy is indicated prior to the onset of irreversible optic nerve damage.

Extensive orbital inflammation in an anophthalmic socket: is the Bioceramic implant a bystander or a participant?

Purpose: Porous orbital implants are commonly used materials following enucleation or evisceration. Implant-associated inflammation is a rare but serious complication which may necessitate explantation. Observations: We report a case of a patient who developed extensive orbital inflammation six months after implantation of a vicryl (polyglactin 910) mesh-wrapped Bioceramic (aluminum oxide) spherical implant. An orbital biopsy demonstrated an extensive fibroinflammatory reaction with multinucleated giant cells. Removal of the implant resulted in complete resolution of symptoms. Conclusions and importance: We surmise that the Bioceramic implant played a significant contributory role in this patient's orbital inflammation, a complication which has not been described previously.

Extraocular muscle enlargement.

Extraocular muscle enlargement can occur secondary to a range of orbital and systemic diseases. Although the most common cause of extraocular muscle enlargement is thyroid eye disease, a range of other inflammatory, infective, neoplastic, and vascular conditions can alter the size and shape of the extraocular muscles. Imaging with computed tomography and magnetic resonance imaging plays an essential role in the workup of these conditions. This article provides an image-rich review of the wide range of pathology that can cause enlargement of the extraocular muscles.

Diagnostic Utility of Diffusion-Weighted Imaging and Apparent Diffusion Coefficient for Common Orbital Lesions: A Review.

PURPOSE: To review and summarize the existing literature surrounding the clinical use of diffusion-weighted imaging and apparent diffusion coefficient (ADC) as diagnostic tools in differentiating common orbital lesions. METHODS: A systematic literature review on the use of ADC and diffusion-weighted imaging sequences for orbital imaging was performed. Only original research articles that reported ADC values for benign or malignant lesions were included. RESULTS: Malignant orbital tumors have an overall lower mean ADC value than benign masses. Orbital lymphoma is characterized by consistently lower ADC values compared with other malignant orbital masses; a threshold value less than 0.775 × 10 -3 mm 2 /s has been proposed to distinguish orbital lymphoma from other neoplastic and non-neoplastic orbital masses. To differentiate orbital inflammatory disease from lymphoma, an ADC threshold greater than 0.92 × 10 -3 mm 2 /s has been proposed. CONCLUSIONS: Orbital masses encompass a host of benign and malignant etiologies and can present a diagnostic challenge on both clinical and radiological assessment. Recent advanced MRI techniques such as diffusion-weighted imaging and ADC can improve the diagnostic specificity for orbital disease, particularly in differentiating benign from malignant lesions and lymphoma from orbital inflammatory disease.

Primary leptomeningeal low-grade Schwann cell neoplasm.

We discuss an extremely rare case of low-grade Schwann cell leptomeningeal neoplasm with no evident intradural primary, presenting with rapid neurological decline leading to death reflecting the aggressive biological behaviour of this entity despite its low-grade morphology. Notwithstanding extensive investigations, the diagnosis was only established on autopsy as clinical presentation is non-specific making diagnosis challenging. This condition could be considered in patients presenting with leptomeningeal disease if initial workup of more common causes is non-revealing.