Functional imaging of thymic disorders

Human thymomas are rare tumours which usually develop in the chest. The diagnosis via guided biopsy, the evaluation of the extent of the tumour and its boundaries with adjacent organs, the choice of the appropriate therapeutic option, and the assessment of response to treatment are usually made with computed tomography (CT) alone or in combination with magnetic resonance imaging (MRI). More recently, radiopharmaceuticals and nuclear medicine procedures have been used increasingly in the imaging and functional characterization of benign and malignant thymic disorders. Two groups of radiopharmaceuticals have been used. The first includes several oncotropic tracers, such as 201Tl-chloride, 99mTc-sestamibi and 18F-fluorodeoxyglucose, which are significantly concentrated in thymic tumours. Their uptake correlates with tumour grades and cellularity. The second class includes two radioligands: [(111)In-DTPA-D-Phe1]-octreotide (DTPA, diethylenetriamine penta-acetic acid) and [(111)In-DTPA-Arg1]-substance P, which bind to specific receptors. [(111)In-DTPA-Arg1]-substance P binds to its receptors that are largely expressed in the thymus of patients with autoimmune diseases. [(111)In-DTPA-D-Phe1]-octreotide recognizes the somatostatin receptor subtype 2. In patients with active disease investigated in our institution [(111)In-DTPA-D-Phe1]-octreotide has been shown to concentrate in the majority of thymoma deposits. Conversely, it is not concentrated in adult patients with benign lymphofollicular thymic hyperplasia. This finding has had a significant impact on the management of patients with myasthenia gravis as it differentiates early-stage thymoma from benign hyperplasia, unlike CT and MRI, which often fail to distinguish between the two. In addition to its role in diagnostic imaging, somatostatin receptor scintigraphy also enables us to select patients with advanced or metastatic thymoma unresponsive to conventional therapies, who might benefit from a somatostatin analogue-based treatment, serving thus as a link between diagnosis and therapy. In this article, we discuss and analyse the results of functional imaging with different radiopharmaceuticals, primarily those that we have obtained with [(111)In-DTPA-D-Phe1]-octreotide.     

Morphological imaging of thymic disorders

The thymus is a bilobed lymphoid organ the morphology of which varies considerably with age as a result of a process of fatty infiltration occurring after puberty. Although several diseases can arise in the thymic parenchyma, including germ cell and neuroendocrine tumours, primitive epithelial neoplasms (thymomas) are the most common neoplasms and account for almost 10% of mediastinal masses. Thymomas are usually benign but can be locally invasive. Up to 30% of patients with a thymoma have myasthenia gravis, which is more commonly associated with thymic hyperplasia. The latter results in a symmetric diffuse enlargement of the thymus. However, thymic hyperplasia can be histologically found in up to 50% of normal-sized thymuses on computed tomography (CT). CT is much more accurate in detecting thymomas than it is in detecting thymic hyperplasia, although CT findings may be unspecific. CT can be exhaustive in the case of an encapsulated thymoma (65% of all thymomas), which appear as a solid homogeneous mass with a slight contrast enhancement and a well-defined surrounding fat plane. These tumours rarely recur after surgery. CT can also accurately detect a spread through the capsule into the adjacent mediastinal fat, which characterizes invasive thymomas (35%). These, however, are best evaluated by magnetic resonance imaging (MRI). On T1-weighted MR scans the thymus is well delineated against the mediastinal fat, whereas marked inhomogeneity of the signal may appear on T2-weighted images as a result of areas of cystic degeneration in the tumour mass. The superior contrast resolution of MRI and the multiplanar images that can be produced with it are well suited for documenting the mediastinal spread of invasive thymomas. MRI depicts accurately pleural and/or pericardial implants as well as the involvement of great vessels, offering considerable aid in the planning of surgery.     

Pathological aspects of malignant and benign thymic disorders

A WHO committee recently defined criteria for distinguishing between thymic epithelial tumours (TET) and classified them as type A, AB, B1-3 and C thymomas. As the terminology for each WHO type is still controversial, it is recommended to use also other names in addition to the WHO classification to allow comparability of future clinicopathological studies. We consider type A and AB thymomas (medullary and mixed thymomas) clinically benign, whereas type B1-3 thymomas (predominantly cortical and cortical thymomas and well-differentiated thymic carcinomas) are of low-grade malignant potential and most type C thymomas (category II malignant thymomas) are highly malignant. Not yet approved by the WHO are the recently described 'thymoma with pseudosarcomatous stroma' and the 'low-grade metaplastic carcinoma of the thymus', which are considered as benign or low-grade malignant tumours, respectively. Thymic pathology frequently occurs in myasthenia gravis (MG). Production of autoantibodies against the acetylcholine receptor results from an antigen-driven immune reaction that starts inside the thymus, is maintained there but spreads to extrathymic sites already during the early phase of MG. Paraneoplastic MG occurs only in type A, AB and B1-3 thymomas. Abnormal TET microenvironments trigger nontolerogenic T-cell selection by neoplastic epithelial cells. Only after export of substantial numbers of naive, potentially autoreactive T cells to extratumorous sites does T-cell activation outside the thymoma initiate the autoimmune process. Early surgery after onset of MG is essential in thymitis to prevent substantial export of autoreactive T cells from the inflamed thymus to extrathymic organs, and it usually alleviates MG symptoms. In thymoma, 'dissemination' of autoreactive T cells to extratumorous sites has already continued for many months or even years before emergence of symptoms of MG. Therefore, thymoma surgery is aimed against oncological and local cardiovascular complications and rarely succeeds in alleviating symptoms of MG.     

Role of iron in neurodegenerative disorders

Although the pathophysiology underlying a number of neurodegenerative diseases is complex and, in many aspects, only partly understood, increased iron levels in pathologically relevant brain areas and iron-mediated oxidative stress seem to play a central role in many of them. Much has been learned from monogenetically caused disturbances of brain iron metabolism including pantothenate kinase-associated neurodegeneration type 2, hereditary ferritinopathies affecting the basal ganglia, and aceruloplasminemia that may well be applied to the most common neurodegenerative disorders associated with brain iron accumulation including Parkinson disease and Alzheimer disease. Iron-mediated oxidative stress in neurodegenerative diseases caused by other genetic pathways like Huntington disease and Friedreich ataxia underscore the complex interaction of this trace metal and genetic variations. Therapeutical strategies derived from application of iron chelators in monogenetically caused disturbances of brain iron metabolism and new iron and oxidative stress diminishing substances in animal models of Parkinson disease are promising and warrant further investigational effort.     

心理疗法在精神疾病治疗中的作用

心理治疗在不同类精神疾病治疗中主要作用有：心理教育、增加患者对治疗的依从、作为辅助性治疗和对大部分神经症作为主要的治疗方法,在心理治疗应用于精神疾病治疗时也有许多应注意的问题。     

Role of natriuretic peptides in cardiovascular surgery

Acute kidney injury is a major complication of cardiovascular surgery. Therapies to reduce or prevent acute kidney injury are highly desirable, and recent advances have helped refine the targets for such therapy, albeit with surprises and controversies. Among these therapies, natriuretic peptides have received the most scrutiny owing to the difficulty in explaining the conflicting evidence for effectiveness in some, but lack thereof, in other studies. This article examines the possible reasons for the conflicting results reported with natriuretic peptides in various clinical conditions.     

Role of thymic peptides as transmitters between the neuroendocrine and immune systems

Thymic peptides, a heterogenous family of polypeptidic hormones synthesized within the thymus, not only exert important regulatory effects within both the immune and neuroendocrine systems but are also themselves subject to control by hormones derived from the hypothalamic-pituitary-adrenal axis (HPA) and other endocrine glands. Regarding thymic hormonal function, thymulin production is up-regulated by several hormones, including prolactin, growth hormone and thyroid hormones. Other aspects of the physiology of thymic epithelial cells can also be modulated by hormones and neuropeptides, particularly cytokeratin expression, cell growth and production of extracellular matrix proteins, thus characterizing the pleiotrophic action of these molecules on the thymic epithelium. Conversely, thymic-derived peptides also regulate hormone release from the HPA axis and may act directly on target endocrine glands of this axis, modulating gonadal tissues. In addition, it has recently been shown that thymulin can modulate some peripheral nervous sensory functions, including those related to sensitivity to pain. According to the dose given, thymulin induces or reduces hyperalgesia related to both mechanical and thermal nociceptors and thus represents an important interface between the immune, endocrine and nervous systems.     

Role of neuroimaging in the management of seizure disorders

Neuroimaging is one of the most important advances made in the past decade in the management of seizure disorders. Magnetic resonance imaging (MRI) has increased substantially the ability to detect causes of seizure disorders, to plan medical or surgical therapy, and to prognosticate the outcome of disorders and therapy. However, MRI must be performed with techniques that will maximize the detection of potentially epileptogenic lesions, especially in candidates for epilepsy surgery. Functional imaging has an established role in evaluating patients for epilepsy surgery. It is relied on when results from standard diagnostic methods, such as clinical information, electroencephalography, and MRI, are insufficient to localize the seizure focus. Also, functional imaging is a reportedly reliable alternative to invasive methods for identifying language, memory, and sensorimotor areas of the cerebral cortex. Despite the availability of multimodality imaging, the epileptogenic zone is not determined solely by a single imaging modality. Evidence and experience have shown that concordance of results from clinical, electrophysiologic, and neuroimaging studies is needed to identify the epileptogenic zone accurately. With modern techniques in image processing, multimodality imaging can integrate the location of abnormal electroencephalographic, structural, and functional imaging foci on a "map" of the patient's brain. Computer image-guided surgery allows surgically exact implantation of intracranial electrodes and resection of abnormal structural or functional imaging foci. These techniques decrease the risk of morbidity associated with epilepsy surgery and enhance the probability of postsurgical seizure control.     

Role of magnetic resonance imaging in fetal surgery

Prenatal magnetic resonance imaging (MRI) has several advantages over obstetric ultrasound, including a larger field of view, superior soft-tissue contrast, more precise volumetric measurements, and greater accuracy in the demonstration of intracranial abnormalities. Prenatal MRI has been shown to positively and incrementally influence management in a substantial proportion of patients being considered for fetal intervention. Despite these findings, precise indications for prenatal MRI in the setting of fetal surgery are not yet established, because both prenatal MRI and fetal surgery are relatively new techniques that remain in evolution. Conditions in which prenatal MRI appears to contribute to fetal surgical planning and postoperative evaluation are described in this review. These conditions include congenital diaphragmatic hernia, cystic adenomatoid malformation, sacrococcygeal teratoma, complicated twin pregnancies, upper airway obstruction, and myelomeningocele.     

Role of prophylactic ureteric stents in colorectal surgery

Ureteric injury is a feared complication in colorectal surgery, with a reported incidence of 0.2%-7.6%. Prophylactic ureteric catheter placement has the advantage of facilitating intraoperative ureter identification and assisting in immediate injury recognition and repair. However, its use has been controversial because of fear of ureteric damage during catheter insertion and postoperative urinary complications such as obstructive oliguria and urinary tract infection. Although the exact indications for prophylactic catheter placement are not clearly defined, it is generally used for reoperative cases, large tumors, previous radiation therapy, diverticulitis, fistulas, Crohn's disease and obesity. Herein, we review the incidence and risk factors for ureteric injury, the role of prophylactic ureteric stents and the complications and costs associated with its use in both open and laparoscopic colorectal surgery.     

Role of99mTc-IDA cholescintigraphy in evaluating biliary tract disorders

Technetium-99m IDA cholescintigraphy has provided a new, noninvasive means of visualizing biliary tract function. It has become the procedure of choice in patients with suspected acute cholecystitis because of its ability to most accurately detect functional obstruction or patency of the cystic duct as opposed to ultrasound's ability to detect only anatomic changes such as the presence of calculi or a thickened gallbladder wall. These latter findings are more important in establishing the diagnosis of chronic cholecystitis where ultrasound shares a position of prime importance with the oral cholecystogram. Tc-99m IDA cholescintigraphy has also been particularly useful in evaluating bile leaks, biliary-enteric anastomosis patency and the post-cholecystectomy patient with recurrent pain. In the patient with cholestasis, ultrasound is usually the procedure of choice since it establishes whether or not ductal dilatation is present and frequently can determine the cause of obstruction. Cholescintigraphy has played an ancillary role in many cases by demonstrating the level of partial obstruction, but it does not have the anatomic resolution to visualize the cause of obstruction. Occasionally, in the evaluation of cholestasis, cholescintigraphy has proven to be the only modality which has identified the presence of acute common duct obstruction or localized intrahepatic ductal obstruction. All in all, Tc-99m IDA cholescintigraphy has had a dramatic impact upon hepatobiliary diagnosis.