Imaging of stroke: Part 2, Pathophysiology at the molecular and cellular levels and corresponding imaging changes.

OBJECTIVE: Stroke is the third leading cause of death and the leading cause of severe disability. During the "decade of the brain" in the 1990s, the most promising development was the treatment of acute ischemic stroke. It is thought to result from a cascade of events from energy depletion to cell death. In the initial minutes to hour, clinical deficit does not necessarily reflect irreversible damage. The final outcome and residual deficit will be decided by how fast reperfusion is achieved, which in turn depends on how early the diagnosis is made. This article explains the pathophysiology of stroke at the molecular and cellular levels with corresponding changes on various imaging techniques. CONCLUSION: The pathophysiology of stroke has several complex mechanisms. Understanding these mechanisms is essential to derive neuroprotective agents that limit neuronal damage after ischemia. Imaging and clinical strategies aimed at extending the therapeutic window for reperfusion treatment with mechanical and pharmacologic thrombolysis will add value to existing treatment strategies. Acute ischemic stroke is defined as abrupt neurologic dysfunction due to focal brain ischemia resulting in persistent neurologic deficit accompanied by characteristic abnormalities on brain imaging. Knowledge of the pathophysiologic mechanisms of neuronal injury in stroke is essential to target treatment. Neuroprotective and thrombolytic agents have been shown to improve clinical outcome. Physiologic imaging with diffusion-weighted imaging (DWI) and perfusion CT and MRI provide a pathophysiologic substrate of evolving ischemic stroke.

Optimization of patient dose and image quality with z-axis dose modulation for computed tomography (CT) head in acute head trauma and stroke.

The purpose of this study is to retrospectively analyze the effect of z-axis modulation for CT head protocols on patient dose and image quality in patients with acute head trauma and stroke. The study was approved by the Institutional Review Board. We retrospectively evaluated the effect of dose modulation on unenhanced CT head examinations in patients with acute head trauma and stroke. Two series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation. Multidetector 16-section CT was performed sequentially and axial 5-mm-thick slices were obtained from base of skull to vertex. With z-axis dose modulation, the same tube current range was maintained, but a computer algorithm altered the tube current applied to each CT section. For each examination, the weighted volume CT dose index (CTDI (vol)) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality by two independent, blinded readers. The variables (CTDI (vol) and DLP, image quality, and noise) in the two groups were compared by using student t test and Wilcoxon rank-sum test. For unenhanced CT head examinations, the CTDI (vol) and DLP, respectively, were reduced by 35.8% and 35.2%, respectively, by using z-axis dose modulation. Image quality and noise were unaffected by the use of this dose modulation technique (P < 0.004). Utilization of z-axis modulation technique for CT head examination in patients with acute head trauma and stroke offers significant radiation dose reduction while image quality is optimally maintained.

Osseous Changes Over Time in Free Fibular Flap Reconstruction.

OBJECTIVES/HYPOTHESIS: Evaluate bone resorption in free fibular grafts and document resorption behavior as compared to dentulous and edentulous autochthonous mandibular bone. STUDY DESIGN: Retrospective Chart review. METHODS: Postoperative computed tomography images were used to evaluate fibular graft resorption rates and corresponding sites of the dentulous or edentulous mandible. Bone height, width, and cortical thickness were measured. RESULTS: Eighteen patients underwent fibula free flap reconstruction following resection of a primary head and neck cancer. Mandibular defects were classified using Jewer's classification. The average interval loss of osseous height was 0.23 ± 0.09 mm/yr for fibula flap, 0.55 ± 0.13 mm/yr for dentulous native mandible, and 0.98 ± 0.41 mm/yr in edentulous native mandible. Change in osseous width was 0.19 ± 0.08 mm/yr, 0.55 ± 0.33 mm/yr, and 0.73 ± 0.15 mm/yr, respectively. Rate of superior cortical resorption was 0.33 ± 0.34 mm/yr, 0.35 ± 0.13 mm/yr, and 0.53 ± 0.11 mm/yr in fibula flap, dentulous, and edentulous mandible, respectively. Inferior cortical resorption rates were quantified as 0.30 ± 0.11 mm/yr, 0.35 ± 0.08 mm/yr, and 0.51 ± 0.08 mm/yr. CONCLUSIONS: Fibula free flap reconstruction of the mandible provides excellent functional results and allows for stable outcomes. Bone resorption is significantly lower in fibular graft compared with both edentulous and dentulous mandible. Edentulous bone displays significantly increased rates of atrophy in comparison to the dentulous mandible. This may have implications with regard to long-term viability of both the fibular flap and native mandible. The role of dental restoration on overall osseous stability warrants further research. LEVEL OF EVIDENCE: 4 Laryngoscope, 129:1113-1116, 2019.

Imaging of Submandibular and Sublingual Salivary Glands.

The submandibular and sublingual salivary glands are major salivary glands with a wide spectrum of pathologic conditions. The corresponding spaces along the floor of mouth have complex anatomy, best evaluated with cross-sectional imaging. The spectrum of diseases in these regions varies from simple infection to advanced malignancy, not just from the gland itself but also from the surrounding structures. The most common abnormalities in these spaces are inflammatory and infectious, and computed tomography is currently the most common imaging modality used. The anatomy of these spaces is much better depicted with MR; however, all the modalities have their unique roles.

Imaging anatomy of deep neck spaces.

This article presents a comprehensive analysis of the neck fascia and neck spaces that are formed by the interplay of the different fascial layers. Because a solid and thorough understanding of the anatomy and relationship of the various neck spaces is so valuable in diagnosing and treating diseases of the neck, this information organizes the anatomic areas of the neck beginning with and overview, followed by extent, anatomic relationship, and contents. Detailed enhanced computed tomography images display the anatomic areas of the neck.

Submandibular and sublingual spaces: diagnostic imaging and evaluation.

The mylohyoid muscle divides the lower part of the oral cavity into 2 spaces: the sublingual space, which is located superior to the muscle, and the submandibular space, inferior to the muscle but superior to the hyoid bone. Although the submandibular and sublingual spaces are small, a wide range of pathologic processes may involve these spaces. They include cystic lesions, inflammatory conditions with various causes, rare vascular lesions, and benign and malignant neoplasms. This article outlines the radiologic anatomy of the region, describes the various pathologic processes that may affect it, and discusses the use of imaging in their evaluation.

Parotid space: anatomic imaging.

The authors present imaging anatomy of the parotid space and discuss non-neoplastic lesions, autoimmune disorders, cysts, neoplastic lesions, epithelial tumors, and nonepithelial lesions. They describe the diseases and their appearance on imaging, describing how the differential diagnoses appear, along with presenting examples of the images, primarily computed tomography and magnetic resonance imaging.

Imaging of the carotid space.

The most common of the lesions in the carotid space are discussed in relation to their radiographic diagnosis and clinical implications. The appearance of tumors and lesions on computed tomography or magnetic resonance imaging is presented, and their differential diagnosis is discussed. The image of each carotid disease is presented, and the discussion concludes with treatment recommendations and considerations.

Ethylene Glycol Toxicity: Chemistry, Pathogenesis, and Imaging.

The ingestion of ethylene glycol results in toxicity with characteristic chemical, pathological, and imaging findings. In the case presented, magnetic resonance imaging demonstrated bilateral symmetric hyperintensity within the basal ganglia, thalami, and brainstem. Ethylene glycol toxicity also resulted in restricted diffusion within the white matter tracts of the corona radiata, a finding not previously described in the literature. In the acute clinical setting, ethylene glycol toxicity is an important differential consideration of the pathologies involving the deep grey matter nuclei.