Surjith Vattoth

Radiation Necrosis in the Brain: Imaging Features and Differentiation from Tumor Recurrence

Radiation necrosis in the brain commonly occurs in three distinct clinical scenarios, namely, radiation therapy for head and neck malignancy or intracranial extraaxial tumor, stereotactic radiation therapy (including radiosurgery) for brain metastasis, and radiation therapy for primary brain tumors. Knowledge of the radiation treatment plan, amount of brain tissue included in the radiation port, type of radiation, location of the primary malignancy, and amount of time elapsed since radiation therapy is extremely important in determining whether the imaging abnormality represents radiation necrosis or recurrent tumor. Conventional magnetic resonance (MR) imaging findings of these two entities overlap considerably, and even at histopathologic analysis, tumor mixed with radiation necrosis is a common finding. Advanced imaging modalities such as diffusion tensor imaging and perfusion MR imaging (with calculation of certain specific parameters such as apparent diffusion coefficient ratios, relative peak height, and percentage of signal recovery), MR spectroscopy, and positron emission tomography can be useful in differentiating between recurrent tumor and radiation necrosis. In everyday practice, the visual assessment of diffusion-weighted and perfusion images may also be helpful by favoring one diagnosis over the other, with restricted diffusion and an elevated relative cerebral blood volume being seen much more frequently in recurrent tumor than in radiation necrosis.

A Compartment-Based Approach for the Imaging Evaluation of Tinnitus

SUMMARY: Tinnitus affects 10% of the US general population and is a common indication for imaging studies. We describe a sequential compartment-based diagnostic approach, which simplifies the interpretation of imaging studies in patients with tinnitus. The choice of the initial imaging technique depends on the type of tinnitus, associated symptoms, and examination findings. Familiarity with the pathophysiologic mechanisms of tinnitus and the imaging findings is a prerequisite for a tailored diagnostic approach by the radiologist.

Susac syndrome in a young child

Susac syndrome is a microangiopathy of unknown origin affecting the brain, retina and inner ear. This rare entity is often misdiagnosed as a demyelinating condition such as multiple sclerosis or acute disseminated encephalomyelitis. A high index of suspicion must be present as the majority of patients do not have the complete clinical triad at the time of onset of symptoms. The radiologist plays an important role when the disease is suspected and helps orient the investigations. The syndrome has characteristic imaging features on MRI that include multifocal white matter and occasional grey matter lesions, the corpus callosum being always involved. The predominant central callosal lesions, especially with rapid cystic transformation (central callosal holes) can be considered pathognomonic of this condition in the appropriate clinical setting. This disease is extremely rare in children. We report a case of Susac syndrome in a 9-year-old girl to increase the awareness among paediatric radiologists of this entity, which is usually not considered as a differential diagnosis of multifocal white matter involvement in this age group.

MR Anatomy of Deep Brain Nuclei with Special Reference to Specific Diseases and Deep Brain Stimulation Localization

Diseases affecting the basal ganglia and deep brain structures vary widely in etiology and include metabolic, infectious, ischemic, and neurodegenerative conditions. Some neurologic diseases, such as Wernicke encephalopathy or pseudohypoparathyroidism, require specific treatments, which if unrecognized could lead to further complications. Other pathologies, such as hypertrophic olivary degeneration, if not properly diagnosed may be mistaken for a primary medullary neoplasm and create unnecessary concern. The deep brain structures are complex and can be difficult to distinguish on routine imaging. It is imperative that radiologists first understand the intrinsic anatomic relationships between the different basal ganglia nuclei and deep brain structures with magnetic resonance (MR) imaging. It is important to understand the “normal” MR signal characteristics, locations, and appearances of these structures. This is essential to recognizing diseases affecting the basal ganglia and deep brain structures, especially since most of these diseases result in symmetrical, and therefore less noticeable, abnormalities. It is also crucial that neurosurgeons correctly identify the deep brain nuclei presurgically for positioning deep brain stimulator leads, the most important being the subthalamic nucleus for Parkinson syndromes and the thalamic ventral intermediate nucleus for essential tremor. Radiologists will be able to better assist clinicians in diagnosis and treatment once they are able to accurately localize specific deep brain structures.

Surgical Approaches to Central Skull Base and Postsurgical Imaging

The close proximity to or intricate involvement of critical neurovascular structures in the central skull base region or both present unique surgical challenges. Varied surgical approaches may be used to remove tumors in this region, including open craniotomies and minimally invasive transnasal or transfacial endoscopic approaches. The ideal surgical technique is chosen based on multiple factors including the aggressiveness, histopathology, and location of the tumor with respect to regional neurovascular elements. Postsurgical image analysis of the central skull base requires an intimate understanding of preoperative and expected postoperative appearance in relation to the nature of the excision and surgical materials used.

A practical review of the muscles of facial mimicry with special emphasis on the superficial musculoaponeurotic system.

OBJECTIVE In this article, we elaborate a practical approach to superficial facial anatomy enabling easy identification of the facial mimic muscles by classifying them according to their shared common insertion sites. CONCLUSION The facial mimic muscles are often difficult to identify on imaging. By tracing them from their common group insertion sites back to their individual origins as well as understanding key anatomic relationships, radiologists can more accurately identify these muscles.

Reversible Blindness in Cryptococcal Meningitis With Normal Intracranial Pressure: Case Report and Review of the Literature

Ocular complications in cryptococcal meningitis (CM) are commonly attributed to elevated intracranial pressure (ICP). We report a case of reversible vision loss complicating AIDS-related CM with a normal ICP. We review other cases of blindness in CM with normal ICP and the potential role of corticosteroids as treatment.

Vascular Lesions of the Central Skull Base Region

The arterial and venous structures of the central skull base region form complex anatomical relationships with each other and with adjacent osseous and neural structures. Vascular structures including the cavernous sinuses and internal carotid arteries can be displaced, encased, or invaded by neoplastic, inflammatory, or infectious lesions of the central skull base. Consequently, the vascular structures have a unique role in determining the imaging appearance, clinical significance, and therapeutic options of lesions occurring in the central skull base. This article briefly reviews the basic anatomy of the cavernous sinus and the relationship of the internal carotid artery to the cavernous sinus and central skull base. The major imaging features of some common vascular lesions, including skull base aneurysm, carotid-cavernous fistula, and cavernous sinus thrombosis are presented.

Unusual appearance and presentation of supratentorial subependymoma in an adult patient.

We report a case of a large, heterogeneously enhancing, pathologically proven, supratentorial subependymoma in a 31-year-old male patient presenting with headache, nausea and vomiting as well as gait disturbances. Although most supratentorial subependymomas have distinctive MR features, our case demonstrated imaging findings that made it indistinguishable from other more aggressive malignant supratentorial intraventricular lesions. It is of paramount importance to consider supratentorial subependymomas in the differential diagnosis of supratentorial lesions, even if their radiological features were atypical.

Primary Hyperparathyroidism-Related Brown Tumors Mimicking Other Giant Cell-Containing Skeletal Tumors: Role of Correlative Imaging in Diagnosis

A patient initially suspected of having a giant cell granuloma was subsequently found—through additional imaging with 99mTc-sestamibi and ultrasound—to have osteolytic brown tumors caused by a parathyroid adenoma. Brown tumors that relate to primary hyperparathyroidism may mimic other skeletal tumors that contain giant cells, presenting difficulty with accurate diagnosis. Correlative imaging can have a valuable role in such cases, potentially avoiding the extensive work-up usually done for suspected bone metastases.