High resolution 3D magnetic resonance imaging of Gruber's ligament: a pilot study.

INTRODUCTION: Gruber's ligament (GL), a surgical landmark, extends from the lateral upper clivus to the petrous apex (PA), forming the superior boundary of Dorello's canal (DC). It overlies the interdural segment of the abducens nerve (CN VI). High-resolution 3D skull base MRI (SB-MRI) demonstrates anatomic details visible to the surgeon, but not well seen on traditional cross-sectional imaging. The aim of this study was to demonstrate visualization of the GL and its relationship to CN VI utilizing contrast enhanced high-resolution SB-MRI. METHODS: Two neuroradiologists retrospectively reviewed in consensus the SB-MRIs of 27 skull base sides, among 14 patients. GL detection rate, confidence of detection, and GL length were recorded. When GL was successfully identified, the position of the interdural segment of CN VI within DC was recorded. RESULTS: GL was readily identified in 16 skull base sides (59%), identified with some difficulty in 2 skull base sides (7%), and failed to be identified in 9 skull base sides (33%). The mean GL length was 7.1 mm (4.5-9.3 mm). Among the 18 cases where GL was successfully identified, CN VI was readily identified in all cases (100%), coursing the lateral third of DC in 72% of sides, and middle third in the remaining 28% of sides. CONCLUSION: GL can be identified in approximately two-thirds of cases utilizing 3D high resolution SB-MRI. CN VI passes most commonly along the lateral third of DC. This is the first report demonstrating visualization of GL and its relation to CN VI, on imaging.

Systematic volumetric analysis predicts response to CSF drainage and outcome to shunt surgery in idiopathic normal pressure hydrocephalus.

OBJECTIVES: Idiopathic normal pressure hydrocephalus (INPH) is a neurodegenerative disorder characterized by excess cerebrospinal fluid (CSF) in the ventricles, which can be diagnosed by invasive CSF drainage test and treated by shunt placement. Here, we aim to investigate the diagnostic and prognostic power of systematic volumetric analysis based on brain structural MRI for INPH. METHODS: We performed a retrospective study with a cohort of 104 probable INPH patients who underwent CSF drainage tests and another cohort of 41 INPH patients who had shunt placement. High-resolution T1-weighted images of the patients were segmented using an automated pipeline into 283 structures that are grouped into different granularity levels for volumetric analysis. Volumes at multi-granularity levels were used in a recursive feature elimination model to classify CSF drainage responders and non-responders. We then used pre-surgical brain volumes to predict Tinetti and MMSE scores after shunting, based on the least absolute shrinkage and selection operator. RESULTS: The classification accuracy of differentiating the CSF drainage responders and non-responders increased as the granularity increased. The highest diagnostic accuracy was achieved at the finest segmentation with a sensitivity/specificity/precision/accuracy of 0.89/0.91/0.84/0.90 and an area under the curve of 0.94. The predicted post-surgical neurological scores showed high correlations with the ground truth, with r = 0.80 for Tinetti and r = 0.88 for MMSE. The anatomical features that played important roles in the diagnostic and prognostic tasks were also illustrated. CONCLUSIONS: We demonstrated that volumetric analysis with fine segmentation could reliably differentiate CSF drainage responders from other INPH-like patients, and it could accurately predict the neurological outcomes after shunting. KEY POINTS: • We performed a fully automated segmentation of brain MRI at multiple granularity levels for systematic volumetric analysis of idiopathic normal pressure hydrocephalus (INPH) patients. • We were able to differentiate patients that responded to CSF drainage test with an accuracy of 0.90 and area under the curve of 0.94 in a cohort of 104 probable INPH patients, as well as to predict the post-shunt gait and cognitive scores with a coefficient of 0.80 for Tinetti and 0.88 for MMSE. • Feature analysis showed the inferior lateral ventricle, bilateral hippocampus, and orbital cortex are positive indicators of CSF drainage responders, whereas the posterior deep white matter and parietal subcortical white matter were negative predictors.

Segmental Imaging of the Trochlear Nerve: Anatomic and Pathologic Considerations.

BACKGROUND: The trochlear nerve (the fourth cranial nerve) is the only cranial nerve that arises from the dorsal aspect of the midbrain. The nerve has a lengthy course making it highly susceptible to injury. It is also the smallest cranial nerve and is often difficult to identify on neuroimaging. EVIDENCE ACQUISITION: High-resolution 3-dimensional skull base MRI allows for submillimeter isotropic acquisition and is optimal for cranial nerve evaluation. In this text, the detailed anatomy of the fourth cranial nerve applicable to imaging will be reviewed. RESULTS: Detailed anatomic knowledge of each segment of the trochlear nerve is necessary in patients with trochlear nerve palsy. A systematic approach to identification and assessment of each trochlear nerve segment is essential. Pathologic cases are provided for each segment. CONCLUSIONS: A segmental approach to high-resolution 3-dimensional MRI for the study of the trochlear nerve is suggested.

Twenty-Five Diagnoses on Midline Images of the Brain: From Fetus to Child to Adult.

Midsagittal images of the brain provide a wealth of anatomic information and may show abnormalities that are pathognomonic for particular diagnoses. Using an anatomy-based approach, the authors identify pertinent anatomic structures to serve as a checklist when evaluating these structures. Subregions evaluated include the corpus callosum, pituitary gland and sellar region, pineal gland and pineal region, brainstem, and cerebellum. The authors present 25 conditions with characteristic identifiable abnormalities at midsagittal imaging. Midsagittal views from multiple imaging modalities are shown, including computed tomography, ultrasonography, and magnetic resonance (MR) imaging. Standard MR imaging sequences are shown, as well as fetal MR and sagittal diffusion-weighted images. To demonstrate these conditions, fetal, neonatal, childhood, adolescent, and young adulthood images are reviewed. The differentiation of normal variants is guided by the understanding of anatomy and pathology. When a specific diagnosis is not possible, the authors present information to evaluate differential considerations and discuss when follow-up imaging may be indicated. The authors hope each case will clarify a pertinent differential diagnosis, appropriately guide patient management, and improve understanding of normal anatomy and identification of pathologic entities. It is in these hopes that the authors have presented a checklist of pertinent anatomy and pathologic entities that can build on existing search patterns. Improved confidence and accuracy in the evaluation of midsagittal images will benefit physicians and patients. ©RSNA, 2018.

Visual Defects in Patients With Pituitary Adenomas: The Myth of Bitemporal Hemianopsia.

OBJECTIVE: The objective of this study was to test the hypothesis that bitemporal hemianopsia (BHA) is the most common visual field (VF) defect in patients with pituitary macroadenoma and to assess the degree of optic pathway compression necessary to produce visual defects. MATERIALS AND METHODS: We reviewed the MRI findings and medical records of 119 patients with pituitary macroadenoma who had undergone formal assessment of VFs. We then evaluated the degree of optic pathway displacement caused by the pituitary macroadenoma, as observed on MR images. The classifications of optic pathway displacement included no contact, abutment but no displacement, mild displacement (< 3 mm), and moderate displacement (≥ 3 mm). Qualitative analysis classified VFs as normal or as having defects that were monocular, bitemporal, mixed (bitemporal with additional defects), homonymous, or nonspecific. RESULTS: A total of 89 of 115 patients had an abnormal VF. Only one patient had true BHA. The most common defects were bitemporal or mixed defects (in 49 of 115 patients [42.6%]), likely because more than just the chiasm is often compressed by the pituitary macroadenoma. Classification of optic pathway displacement by the pituitary macroadenoma was as follows: 23 patients had no contact, eight had abutment but no displacement, 27 had mild displacement, and 57 had moderate displacement. In 78 of the 92 patients (84.8%) with pituitary macroadenoma that had contact with the optic pathway, contact was with the optic chiasm and the prechiasmal optic nerve. Of the 49 patients with bitemporal or mixed defects, 42 had moderate displacement of the optic pathway caused by their tumors. CONCLUSION: BHA is exceedingly uncommon in patients with pituitary macroadenoma. However, although bitemporal and mixed defects are the most common abnormal VF findings, they were found in only 42.6% of patients. Such defects rarely occur if the tumor displaces the optic pathway less than 3 mm from baseline.

High-Resolution 3D Magnetic Resonance Imaging of the Sixth Cranial Nerve: Anatomic and Pathologic Considerations by Segment.

BACKGROUND: Weakness of the sixth cranial nerve is the most common cause of an ocular motor cranial nerve palsy. It is often difficult to identify a corresponding abnormality on neuroimaging to correlate with the clinical examination. EVIDENCE ACQUISITION: High-resolution 3D skull base magnetic resonance imaging (MRI) allows for visualization of the sixth nerve along much of its course and may increase sensitivity for abnormalities in regions that previously were challenging to evaluate. In this review, the authors share their experience with high-resolution imaging of the sixth nerve. RESULTS: For each segment, anatomic features visible on high-resolution imaging are described along with relevant pathologic entities. CONCLUSIONS: We present a segmental approach to high-resolution 3D MRI for evaluation of the sixth nerve from the nuclear to the orbital segment.

Clinical features of sellar and suprasellar meningiomas.

Meningiomas account for about 1% of sellar masses. Although they can mimic pituitary adenomas, they are more vascularized and invasive. To gain insights that would enhance our ability to establish a pre-surgical diagnosis of meningioma, we performed a retrospective study of these tumors. Query of the surgical pathology database identified 1,516 meningiomas operated at out institution between January 2000 and May 2012. Cases were matched to the radiology database to identify a strictly defined sellar and/or suprasellar location. We identified 57 meningiomas. F:M ratio was 6:1. The mean age was 52 years (median 50, range 30-78). The most common symptoms were visual disturbance (58%), headache (16%) and incidental finding (12%). The mean duration of symptoms was 13 months. Hyperprolactinemia was found in 36%, with mean value of 51.6 ng/ml (median 41.8, range 22.5-132). Mean maximal diameter was 2.9 cm (median 2.7, range 0.9-6.8), and most tumors enhanced homogeneously on MRI after gadolinium. A "dural tail" sign was reported in a third. The radiologist reported "likely meningioma" in 65%, "possible meningioma" in 8.7%, and pituitary adenoma in 11%. After surgery, visual disturbances improved in most patients (80%) but headache only in 7%. Post-operative complications at 1 and 3 months occurred 38.6 and 33.3% respectively. There was no mortality. Sellar/suprasellar meningiomas represent 4% of all meningiomas, and have a particularly high female predominance. The diagnosis is suggested by the radiologist in approximately 2/3 of the cases. An improved method to differentiate preoperatively these tumors from adenomas would be desirable.

Partial third nerve palsy and ocular neuromyotonia from displacement of posterior communicating artery detected by high-resolution MRI.

Ocular neuromyotonia is an unusual condition in which sustained, undesired contraction of one or more extraocular muscles occurs after normal muscle activation. Although most commonly reported after paraseller cranial irradiation for tumor, chronic nonaneurysmal vascular compression of the third nerve can produce partial ocular motor nerve paresis and ocular neuromyotonia. A 75-year-old woman presented with intermittent left-gaze-evoked binocular diplopia. She had an incomplete right third nerve palsy but became symptomatically diplopic and esotropic upon sustained left gaze. High-resolution brain magnetic resonance imaging showed displacement of the right posterior communicating artery and contact with the right third nerve. Gaze-evoked diplopia resolved with carbamazepine, but a partial third nerve paresis remained.

Investigation of probability maps in deep-learning-based brain ventricle parcellation.

Normal Pressure Hydrocephalus (NPH) is a brain disorder associated with ventriculomegaly. Accurate segmentation of the ventricle system into its sub-compartments from magnetic resonance images (MRIs) could help evaluate NPH patients for surgical intervention. In this paper, we modify a 3D U-net utilizing probability maps to perform accurate ventricle parcellation, even with grossly enlarged ventricles and post-surgery shunt artifacts, from MRIs. Our method achieves a mean dice similarity coefficient (DSC) on whole ventricles for healthy controls of 0.864 ± 0.047 and 0.961 ± 0.024 for NPH patients. Furthermore, with the benefit of probability maps, the proposed method provides superior performance on MRI with grossly enlarged ventricles (mean DSC value of 0.965 ± 0.027) or post-surgery shunt artifacts (mean DSC value of 0.964 ± 0.031). Results indicate that our method provides a high robust parcellation tool on the ventricular systems which is comparable to other state-of-the-art methods.

AUTOMATED VENTRICLE PARCELLATION AND EVAN'S RATIO COMPUTATION IN PRE- AND POST-SURGICAL VENTRICULOMEGALY.

Normal pressure hydrocephalus (NPH) is a brain disorder associated with enlarged ventricles and multiple cognitive and motor symptoms. The degree of ventricular enlargement can be measured using magnetic resonance images (MRIs) and characterized quantitatively using the Evan's ratio (ER). Automatic computation of ER is desired to avoid the extra time and variations associated with manual measurements on MRI. Because shunt surgery is often used to treat NPH, it is necessary that this process be robust to image artifacts caused by the shunt and related implants. In this paper, we propose a 3D regions-of-interest aware (ROI-aware) network for segmenting the ventricles. The method achieves state-of-the-art performance on both pre-surgery MRIs and post-surgery MRIs with artifacts. Based on our segmentation results, we also describe an automated approach to compute ER from these results. Experimental results on multiple datasets demonstrate the potential of the proposed method to assist clinicians in the diagnosis and management of NPH.

Expanded endonasal endoscopic approach for resection of a skull base low-grade smooth muscle neoplasm.

Benign smooth muscle tumors rarely occur in the head and neck and, to the best of our knowledge, have not been reported in the pterygopalatine fossa. In this report, we describe a 15-year-old adolescent who presented with facial pain and was found to have a large skull base tumor centered in the pterygopalatine fossa. The patient underwent an expanded endonasal endoscopic approach for complete resection of this lesion with resolution of his symptoms. Pathology revealed a well-differentiated smooth muscle neoplasm consistent with a leiomyoma. This case adds to the growing body of literature supporting a role for endoscopic procedures in the treatment of skull base pathologies in pediatric patients.

A joint ventricle and WMH segmentation from MRI for evaluation of healthy and pathological changes in the aging brain.

Age-related changes in brain structure include atrophy of the brain parenchyma and white matter changes of presumed vascular origin. Enlargement of the ventricles may occur due to atrophy or impaired cerebrospinal fluid (CSF) circulation. The co-occurrence of these changes in neurodegenerative diseases and in aging brains often requires investigators to take both into account when studying the brain, however, automated segmentation of enlarged ventricles and white matter hyperintensities (WMHs) can be a challenging task. Here, we present a hybrid multi-atlas segmentation and convolutional autoencoder approach for joint ventricle parcellation and WMH segmentation from magnetic resonance images (MRIs). Our fully automated approach uses a convolutional autoencoder to generate a standardized image of grey matter, white matter, CSF, and WMHs, which, in conjunction with labels generated by a multi-atlas segmentation approach, is then fed into a convolutional neural network to parcellate the ventricular system. Hence, our approach does not depend on manually delineated training data for new data sets. The segmentation pipeline was validated on both healthy elderly subjects and subjects with normal pressure hydrocephalus using ground truth manual labels and compared with state-of-the-art segmentation methods. We then applied the method to a cohort of 2401 elderly brains to investigate associations of ventricle volume and WMH load with various demographics and clinical biomarkers, using a multiple regression model. Our results indicate that the ventricle volume and WMH load are both highly variable in a cohort of elderly subjects and there is an independent association between the two, which highlights the importance of taking both the possibility of enlarged ventricles and WMHs into account when studying the aging brain.

The Role of Preoperative Magnetic Resonance Imaging in Assessing Neurovascular Compression Before Microvascular Decompression in Trigeminal Neuralgia.

BACKGROUND: Preoperative magnetic resonance imaging (MRI) is a standard component of the preoperative clinical workup for patients before microvascular decompression (MVD). However, its ability to accurately exclude neurovascular compression of the trigeminal nerve is not well understood. METHODS: We retrospectively reviewed 1020 patients with available preoperative MRI data before microvascular decompression. General patient demographics and clinical characteristics were collected for each case. We recorded both evidence of neurovascular conflict on preoperative MRI radiology notes and intraoperative compression from operative notes. Sensitivity, specificity, positive predictive value, and negative predictive value were determined for general MRI, high-resolution MRI, and non-high resolution. RESULTS: Overall, preoperative MRI before MVD showed a sensitivity of 75.8%, specificity of 65.8%, positive predictive value of 92.4%, and negative predictive value of 33.3% in predicting neurovascular compression of the trigeminal nerve. In particular, MRI was unable to identify 21.0% cases of sole arterial compression, 42.5% cases of sole venous compression, and combined arterial and venous compression in 18.5% of cases. A total of 958 patients (93.9%) underwent high-resolution preoperative MRI with skull base sequences. This imaging showed a sensitivity of 75.6%, specificity of 66.9%, positive predictive value of 92.5% and a negative predictive value of 33.4% in predicting trigeminal nerve neurovascular compression. Non-high-resolution MRI showed a sensitivity of 78.8%, specificity of 50.0%, positive predictive value of 89.1%, and negative predictive value of 31.3%. The negative predictive values of general, high-resolution, and non-high-resolution MRIs were all <50%. CONCLUSIONS: Preoperative MRI may offer a high predictive value for neurovascular conflict and should be part of the standard preoperative care workup for patients with trigeminal neuralgia. However, lack of neurovascular conflict on preoperative imaging is not sufficient to exclude patients from undergoing MVD.

Expanded endonasal endoscopic approach for resection of a large skull base aneurysmal bone cyst in a pediatric patient with extensive cranial fibrous dysplasia.

Aneurysmal bone cysts (ABCs) are uncommon non-neoplastic, hemorrhagic, and expansile osseous lesions. These lesions most commonly occur in the first two decades of life and affect the long bones and spinal column. Skull base involvement is rare. The authors report the case of a 16-year-old boy who presented with acute visual decline and was found to have a large skull base ABC centered in the sphenoid sinus. In addition, the patient had extensive cranial fibrous dysplasia. The patient underwent a staged expanded endonasal endoscopic approach for complete resection of this lesion with excellent return of his vision. This case adds to the growing body of evidence supporting a role for expanded endonasal endoscopic procedures in pediatric patients with skull base pathologies.

Endonasal endoscopic resection of esthesioneuroblastoma: the Johns Hopkins Hospital experience and review of the literature.

Esthesioneuroblastoma is an uncommon malignant tumor originating in the upper nasal cavity. The surgical treatment for this tumor has traditionally been via an open craniofacial resection. Over the past decade, there has been tremendous development in endoscopic techniques. In this report, we performed a retrospective analysis of patients with esthesioneuroblastomas treated with a purely endonasal endoscopic approach and resection at the Johns Hopkins Hospital between January 2005 and April 2010. A total of eight patients with esthesioneuroblastoma, five men and three women, were identified. Six patients were treated for primary disease, and two were treated for tumor recurrence. The modified Kadish staging was A in one patient (12.5%), B in two patients (25%), C in four patients (50%), and D in one patient (12.5%). All patients had a complete resection with negative intraoperative margins. One patient had intraoperative hypertension; there were no perioperative complications. With a mean follow-up of over 27 months, all patients are without evidence of disease. In addition, we reviewed the literature and identified several overlapping case series of patients with esthesioneuroblastoma treated via a purely endoscopic technique. Our series adds to the growing experience of expanded endonasal endoscopic surgery in the treatment of skull base tumors including esthesioneuroblastoma. Longer follow-up on a larger number of patients is required to further demonstrate the utility of endoscopic approaches in the management of this malignancy.