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Thymic hyperplasia presents as an anterior mediastinal mass and poses important diagnostic and therapeutic challenge. Two types of thymic hyperplasia are described: true hyperplasia and follicular hyperplasie. Literature data are peculiar concerning both entities. We aimed to describe the clinical and microscopic characteristics of thymic hyperplasia through a single institution experience during an 11-year-period.Thymic hyperplasia diagnosed during the period between 2009 and 2020 were included.In all, 46 thymic hyperplasias were diagnosed. The 46 patients consisted in 33 women and 13 men with a mean age of 30 years. Microscopic diagnosis concluded to a follicular hyperplasia in 12 cases and a true thymic hyperplasia in 34 cases. The diagnosis of true thymic hyperplasia posed a diagnostic challenge with an involuted thymus in 1 case and a thymolipoma in 1 case. The confrontation with the clinical data allowed retaining the diagnosis.The diagnosis of thymic hyperplasia is based on microscopic features. The confrontation with clinical data and the measurements of the thymus according to the age allow to retain the diagnosis in most challenging cases.

Thymus hyperplasia and Graves' disease association is not well known and is probably not incidental. We report the case of a young woman affected with Graves' disease in which a retrosternal mass was disclosed during a neck ultrasonographic-examination and confirmed by chest CT-examination. Follow-up ultrasound survey showed a decrease in the thymic mass size. Because of various antithyroid drugs allergy, a surgical procedure was performed, during which both her thyroid and thymic mass were removed. The histopathologic examination of this mass confirmed the hyperplasic nature of the thymic bulging. Ninety-one cases of thymus hyperplasia and Graves' disease association have been reported in literature, of which 20 were histologically confirmed. Among these cases 35 showed a thymic mass regression under medical treatment alone. Accordingly, surgical procedures are most frequently unnecessary in such associations because of the thymic mass decrease incurred by antithyroid drug treatment.

Enlargement of the thymus following remission of a cancer treated by chemotherapy poses a problem of differential diagnosis between benign thymic hyperplasia and relapse of a mediastinal tumour.We report the case of a thymic tumour developing 6 months after chemotherapy for ovarian cancer in a woman of 31 years. Because of the risk of a mediastinal recurrence, the patient was submitted to thymectomy by mediastinotomy. Histopathological examination revealed benign thymic hyperplasia in reaction to the chemotherapy. The postoperative course was uneventful.Benign thymic hyperplasia may develop after chemotherapy. It is an inflammatory reaction that subsides after a few months. A multidisciplinary discussion to consider the possibility of benign hyperplasia may save the patient unnecessary surgery.

Myasthenia gravis is a rare, auto-immune neuromuscular junction disorder. Prevalence rates is about 50/1,000000. The disease results from circulating auto-antibody attacks against post-synaptic targets (acetylcholine receptor [AChR] in 80% cases) on the endplate region of the postsynaptic membrane. The diagnosis is supported clinically by transient weakness, increased by activity that can affect eye movements, swallowing, speech, upper and lower limbs, and trunk. There are generalized or focalized forms (as ocular myasthenia). The course is variable and evolved either with attacks or more chronically. Helpful tests for diagnosis are serologic antibodies detection against AChR, decrement of muscle action potential after repetitive nerve stimulations, identification of thymus gland abnormality (frequently associated with myasthenia) by chest computed tomography. Myasthenia gravis treatment is based on oral form of cholinesterase inhibitors, corticosteroids and other immunosuppressive drugs in severe forms. During myasthenia crisis, intraveinous immune globulines or plasma exchanges can be used. Thymectomy is proposed in case of thymus abnormality.

Background. - Female breast cancer is the most frequent cancer, both in incidence and mortality. It is well known that exposure to ionizing radiation increases the risk, but some questions remain concerning low dose and low-dose rate effects and cofactors. These potential effects have to be taken into account to carry out adequate risk assessment on medically exposed populations. A literature review is proposed on this issue. Methods. - A Medline research was undertaken. Keywords used were ionizing radiation, breast cancer and epidemiology. More studies were added through references included in the first list of articles. The focus was placed on studies including quantitative dose-effect relationship analyses. Results. - A latency of five to 10 to 13 years is observed in the appearance of risk. The risk diminishes with age at exposure. A diminution with age at risk is also suspected. The excess relative risk per gray varies between 0.3 and 1.5 for an age at first exposure of 25 years. The study of Hiroshima and Nagasaki survivors shows that risk is increased even if doses are restricted to below 0.5 Gy. Above high doses (20 Gy), the risk no longer increases. This can be interpreted as a cell-killing effect. The excess subsists if doses are fractionated, but a diminution of the effect is suspected. Conclusion. - The effects of exposure to levels of doses used for medical diagnostic are very difficult to study in the general population by epidemiological methods. Only studies conducted on very young children could achieve enough power, because of their high radiosensitivity. Available information on the effects of doses above 0.5 Gy allows extrapolation on maximal effects. Models deduced from existing cohorts can be used to assess risk, with their limits due to associated uncertainties. Preston et al. proposed an excess absolute-risk model, which makes estimates from the more comprehensive cohorts compatible. This model has been retained by the 2006 committee "Biological effects of ionizing radiation" (report VII). © 2008 Elsevier Masson SAS.; Position du problème Le cancer du sein est le cancer le plus fréquent chez la femme, tant en incidence qu’en mortalité. Si l’exposition aux rayonnements ionisants est un facteur de risque reconnu du cancer du sein, certaines questions ne sont pas encore résolues : quantification des effets aux faibles doses et débit de doses, influence des cofacteurs. Ces éléments sont indispensables pour mener des évaluations du risque sanitaire valides sur les populations actuellement exposées : patients, public et professionnels de santé. Nous proposons ici une synthèse de la littérature sur le sujet mettant en relief les études incluant une relation dose–effet. Méthodes Le recueil bibliographique a été réalisé à partir de la base de données « Medline ». Les mots clés utilisés étaient « rayonnements ionisants », « cancer du sein », « épidémiologie ». D’autres études ont été ajoutées grâce aux références incluses dans la première liste d’articles. Résultats Selon les études, l’excès de risque observé survient entre cinq et dix à 13 ans après la première exposition. Le risque diminue avec l’âge à l’exposition. Une diminution du risque avec l’âge au diagnostic est également suspectée. L’ordre de grandeur de l’excès de risque relatif par gray varie selon les études entre 0,2 et 1,5 pour un âge à la première exposition de 25 ans. L’étude réalisée sur les survivantes d’Hiroshima et de Nagasaki indique une augmentation du risque pour les doses inférieures à 0,5 Gy. Au-delà de 20 Gy environ, le risque atteint un plateau qui pourrait être expliqué par une augmentation de la mort cellulaire. Le fractionnement de l’exposition ne fait pas disparaître l’effet, mais une diminution de cet effet est suspectée. Conclusion Les effets de l’exposition aux rayonnements ionisants au niveau des doses délivrées actuellement dans un but diagnostic sont très difficiles à étudier par des méthodes épidémiologiques en population générale. Seuls les effets sur l’enfant en très bas âge pourraient éventuellement être abordés avec suffisamment de puissance, étant donnée la radiosensibilité des jeunes enfants. En revanche, les connaissances actuelles sur les effets des doses à partir de 0,5 Sv permettent par extrapolation d’évaluer les effets maximaux. Des modèles issus des cohortes existantes, peuvent être éventuellement utilisés pour des évaluations de risque, avec leurs limites du fait des incertitudes associées. Preston et al. proposent un modèle en excès de risque absolu, qui rend compatibles les estimations issues des principales cohortes fournissant une relation dose–effet et qui a été retenu en 2006 par le comité « Biological effects of ionizing radiation » (rapport VII).

We report the case of a 36-year-old women with Hodgkin's disease treated with polychemotherapy and bone marrow autograft. Progressive growth of a thymic mass suggested possible relapse four months after treatment withdrawal. This mass did not exhibit gallium-67 uptake but showed strong affinity for 18-FDG (SUV=6.8). Surgical biopsy ruled out recurrence of Hodgkin's disease of the thymus and led to the diagnosis of thymic rebound. The aspect of the thymic compartment returned to normal spontaneously at one year.

Celiac disease is an autoimmune enteropathy that appears on a predisposed genetic background. Its clinical presentation has been extended those last years by varied extradigestive manifestations.This is a case report of a twenty-year-old woman who presented simultaneously a celiac disease and pure red cell aplasia. The IgA and IgG antigliadin antibodies as well as antinuclear, anti-DNA, anti-SSA and anti-SSB antibodies were detected, without any clinical symptom supporting the diagnosis of systemic lupus erythematosus or Sjögren syndrome. Thoracic CT-scan reveals a thymus enlargement and biopsy concludes to thymus hyperplasia at histological examination. Pure red cell aplasia regressed after gluten-free diet, corticoid therapy and thymectomy.This observation, added to the three others paediatric cases previously published in the literature concern an uncommon association between pure red cell aplasia and celiac disease. However, they are not enough to conclude to a direct link between these two disorders. Pure red cell aplasia could represent un new dysimmune manifestation occurring in celiac disease, but this will need to be confirmed with others cases.

Thymic hyperplasia in response to stress is a well known phenomenon. Thymic hyperplasia has also been described after chemotherapeutic treatment for malignancies in children.A three-year-old girl was followed up from the age of 18 months for a left kidney nephroblastoma treated by combination of chemotherapy (vincristin, actinomycin and adriamycin) and surgery. Assessment at the end of treatment was normal. Four months after the end of treatment, pulmonary radiography showed mediastinal enlargement, which was shown to originate in the thymus at thoracic CT scan. A recurrence of the disease was suspected. Biopsy showed thymic hyperplasia without evidence of tumor cells. Mediastinal enlargement then disappeared spontaneously 2 months later.Thymic hyperplasia occurring during remission of a cancer treated by chemotherapy is a diagnostic dilemma as it suggests mediastinal reccurence of the disease. Needle aspiration cytology is an appropriate investigation in thymic hyperplasia. No steroid therapy should be used before histologic diagnosis of thymic hyperplasia.

Graves' disease is rarely associated with hypertrophy of the thymus which takes on a pseudotumor aspect. We observed a case in a 40-year-old woman who presented clinical and biological hyperthyroidism with anti-TSH receptor antibodies, favoring the diagnosis of Graves' disease which was confirmed by scintigraphy. The chest x-ray performed because of chest pain revealed enlargement of the mediastinum. The thoracic CT-scan without contrast injected showed a pseudotumor aspect of the thymus. Medical treatment with anti-thyroid drugs and beta blockers led to regression of the thymus mass. Knowledge of this type of association can avoid unnecessary thymus surgery. The clinical course is favorable irrespective of the type of anti-thyroid drug given.

Hyperplasia of the thymus, an uncommon development following chemotherapy, raises doubt concerning possible tumor recurrence. We report a case of thymic hyperplasia in a 12-year-old girl who was given chemotherapy for a cervicomediastinal lymphoma. Three months after treatment end, dry cough and an enlargered mediastinum suggested recurrence, but histological examination of tissue biopsy demonstrated benign reactive hyperplasia. Outcome was favorable without recurrence after corticosteroid therapy. According to the literature, thymic hyperplasia is neither tumor nor treatment specific. It generally occurs in children but may be observed in young adults. Hyperplasia of the thymus following chemotherapy would appear to be a good prognosis factor.

In myasthenia gravis (MG), the frequency of histologic abnormalities (hyperplasia in young patients, thymoma in older cases) and clinical improvement after thymectomy indicate involvement of the thymus in the pathophysiology of the disease. MG patient thymuses are characterized by the following features: increased amount of B cells (in hyperplasia) and functional abnormalities, mainly activation of B, T and epithelial cells. Moreover, thymic lymphocytes are sensitized to acetylcholine receptor (AChR): first, AChR specific T and B lines can be grown from MG thymus cultures, second, cultured thymic lymphocytes proliferate in the presence of AChR and produce anti-AChR antibodies. AChR molecules are expressed in thymic myoid cells and AChR-like molecules could be displayed at the surface of other cell types. Thus, autosensitization conditions are combined in MG thymus, and potential mechanisms are discussed. It could be a primary event, autosensitization of lymphocytes to AChR taking place initially in the thymus. Or it could be a secondary process, lymphocytes sensitized to AChR in the periphery could be trapped by myoid cells and restimulated in the thymus. In thymoma, autoimmunization occurs differently: the autoimmune process could be initiated by the tumor epithelial cells which express an AChR-like protein. The possible role of severe architectural disturbance in MG thymus (particularly in thymoma), altering thymic lymphocyte selection and maturation is also discussed.

Ectopic ACTH-secreting tumours responsible for paraneoplastic Cushing's syndrome are invisible at radiography in about 50 percent of the cases. In this situation, the current attitude is to correct the hypercorticism and then embark on a regular morphological monitoring in search of the initial tumour with the purpose of removing it. We report the cases of 3 patients who had a paraneoplastic Cushing's syndrome of unknown origin in 1 case and consecutive, in 2 cases, to a bronchial carcinoid tumour initially occult and discovered 30 and 42 months respectively after the onset of the disease. Six to 10 months after hypercorticism was cured with ketoconazole and bilateral adrenalectomy, a thymic mass 2 to 5 cm in length was detected by computerized tomography or magnetic resonance imaging in all 3 patients. At resection of the thymus, performed in 2 cases, a benign hyperplasia of this organ with negative immunohistostaining for ACTH was discovered. This abnormality, seldom reported, seems to result from the abrupt cessation of hypercorticism. It must be known to avoid an unnecessary thymectomy during supervision of patients with paraneoplastic Cushing's syndrome related to a radiologically occult tumour.

Eleven cases of epithelial tumours of the thymus or thymoma and two thymuses without tumour were studied, using immunohistochemistry with anti-keratin antibodies (KL-1) which recognise cyto-keratin with a high molecular weight. In the normal thymus, KL-1 positivity seems to be limited to medullary epithelial elements and in particular Hassal's corpuscles. All the epithelial thymic tumours studied showed a net positivity for KL-1 overall in the tumour cells. This result and the demonstration of more or less well differentiated Hassal's corpuscles in these tumours make one think that these epithelial thymic tumours express some characters in relation with a differentiation of medullary type.

We describe thyroid carcinomas observed in two male patients after cervical irradiation in infancy. In the first case, irradiation was given for cervical angioma and in the second case, for enlarged thymus. A long time interval (16 and 43 years) elapsed between irradiation and the detection of the epitheliomas. The anatomopathological diagnosis was, for the first patient, papillo-vesicular epithelioma and for the second one, anaplastic carcinoma.

Forty operated cases of myasthenia gravis correspond to 14 thymomas, 18 hyperplasias and 8 vestigial thymus : 3 stages, I, 28 stages, II, 6 stages III, 3 stages IV. For vestigial thymus and moderate hyperplasias, cervicotomy was used in 11 cases. Surgery allowed 15 remissions, 12 ameliorations, 11 failures, aggravations and late deaths, and 2 post-operative deaths (one of them avoidable). Apart from its oncologic interest in thymomas (1/3 of the patients), thymectomy is beneficial in 2/3 of the cases of myasthenia gravis in general.

The object of this paper is to briefly review the surgical aspects of the thymic pathology. Thymic cysts and thymic ectopy are usually asymptomatic and are one of the multiple etiologies of cervical masses. Thymic tumors are very rare and may sometimes be difficult to differentiate from simple thymic hyperplasia; being almost always separated from the normal thymic tissue by a dense capsule, they do not tend to extend rapidly. Thymectomy may be indicated in severe myasthenia.