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Target and Organ at Risk DefinitionDose Prescription and Reporting
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
The OARs to be considered will vary greatly according to the anatomical region being treated and the size and the location of the CTV in these regions. The following are examples of the most common OARs that must be considered: Brain: lens of eye, optic chiasm, brain stem.Head and neck: lens of eye, parotid glands, swallowing structures.Thorax: spinal cord, lungs, heart.Abdomen: spinal cord, large bowel, small bowel, kidneys.Pelvis: bladder, rectum, femoral heads, large bowel, small bowel.
Pituitary incidental adenomas
Published in Nadia Barghouthi, Jessica Perini, Endocrine Diseases in Pregnancy and the Postpartum Period, 2021
ImagingThe best imaging modality is MRI with pituitary protocol. In pregnancy, this is usually performed without gadolinium.MRI can demonstrate the presence of impingement on or abutment of the optic chiasm.MRI may show mass effect on surrounding areas of the brain that could cause harm for the patient (e.g. occlusion of vessels).
The Endocrine System and Its Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
The hypothalamus is a small specialized area at the base of the brain lying above and behind the optic chiasm and above the pituitary gland. It serves as the highest integrative center for the two systems regulating the body's metabolic activities. Hypothalamic endocrine activity is influenced by events recorded in the brain and in the central and autonomic nervous systems. Interaction at the cellular level involves polypeptide normones, adenylate cyclase, cyclic adenosine monophosphate (called "cyclic AMP" but written "cAMP"), and calcium ions. The hypothalamus and pituitary glands regulate growth; lactation (production of milk); function of the thyroid, adrenals, and gonads; and hydration (taking in of water) in the body.
Mimics of Optic Neuritis in Neuromyelitis Optica Spectrum Disorder: A Case Report
Published in Neuro-Ophthalmology, 2021
Nandita Prabhat, Karthik Vinay Mahesh, Aastha Takkar, Manjul Tripathi, Chirag Ahuja, Ramandeep Singh
As the clinical features of ON related to NMOSD may overlap with other inflammatory CNS disorders, ancillary investigations, specifically neuroimaging forms an important early step in its diagnosis. Optic neuritis related to NMOSD is characterised by bilateral, and longitudinally extensive involvement, affecting more than half the length of the optic nerves. Preferential compromise of the posterior optic pathway including the intracranial segment of the optic nerve, extending to the optic chiasm is usually noted. The brain lesions are seen in areas where AQP 4 is expressed including the subpial regions, peri-ependymal regions, circumventricular organs, brainstem, chiasm/hypothalamus, and corpus callosum. Forty per cent of patients with NMOSD may also present with a normal orbital MRI.8
Atypical junctional scotoma secondary to optic chiasm atrophy: a case report
Published in Clinical and Experimental Optometry, 2019
A variety of pathologies can affect the integrity of the optic chiasm based on its anatomy. The chiasm is comprised of 2.4 million nerves converging from the two optic nerves and traverse posteriorly to the optic tracts.2015 Temporal retinal fibres remain ipsilateral and pass through the lateral sides of the optic chiasm on their way to the ipsilateral lateral geniculate nucleus.2015 Nasal retinal fibres decussate in the central area of the optic chiasm on their way to the contralateral lateral geniculate nucleus by way of the optic tracts.2015 Approximately 53-per cent of retinal fibres cross in the chiasm while 47-per cent remain ipsilateral.2016 Nasal macular fibres are known to cross more posteriorly in the optic chiasm.2016 Inferior retinal fibres (representing the superior visual field) remain inferior through the chiasm, while the superior retinal fibres (representing the inferior visual field) remain superior through the chiasm.2016 Further, a newer study has found that the nasal retinal fibres cross more posteriorly in the superior parts of the chiasm and more anteriorly in the inferior parts.2015 Given the level of sophistication of optic chiasm anatomy, lesions here can produce a variety of visual field defects and/or vision loss depending on the size and location of the lesion in the chiasm, as described in this case of a junctional scotoma secondary to optic chiasm atrophy.2011
Factors Associated with Occurrence of Radiation-induced Optic Neuropathy at “Safe” Radiation Dosage
Published in Seminars in Ophthalmology, 2018
Pavle Doroslovački, Madhura A. Tamhankar, Grant T. Liu, Kenneth S. Shindler, Gui-Shuang Ying, Michelle Alonso-Basanta
This study was conducted with the approval of the institutional review board and in accordance with all applicable institutional research policies and procedures, as well as all applicable federal and state laws and regulations. The first portion of the study consisted of a retrospective case series of patients with RION seen at our institution. We reviewed the medical records of patients with RION seen by neuro-ophthalmologists (GTL, MT, KSS) at our institution. RION cases were obtained from the personal databases of these providers. Data, including patient age, diagnosis, tumor location, radiation modality, prescribed radiation dose, fractionation, latency of RION development, treatments, presenting visual acuity, and visual acuity at the end of available follow-up, were collected from the patient charts. Where available, the maximum dose to the anterior visual pathways (Dmax) was noted. The anterior visual pathways were defined as the eyes, optic nerves, and optic chiasm for the purposes of this study. Data on the presence or absence of vasculopathic risk factors such as diabetes mellitus, hypertension, hyperlipidemia, and history of smoking were also collected from the charts.