Mediastinum

Nonneoplastic

Other nonneoplastic


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Cite this page: Gulwani H. Other nonneoplastic. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/mediastinumothernonneoplastic.html. Accessed October 16th, 2021.
Acute thymic involution

Definition / general
  • Due to stress (chronic debilitating disease), HIV or other infections, prolonged protein malnutrition and immunosuppressive or cytotoxic drugs, graft versus host reaction
  • Seen in newborn infants with chorioamnionitis and sepsis
  • Thymus size is significantly reduced in preterm infants born to mothers with subclinical, histologically proven chorioamnionitis (Hum Pathol 2000;31:1121)

Microscopic (histologic) description
  • Preservation of lobular architecture and Hassall corpuscles but marked lymphocyte depletion (particularly with HIV)
  • Vessels are large compared to size of lobules
  • Frequent plasma cells, fibrohyaline changes of basement membrane of vessels and thymic epithelium
  • HIV patients also have effacement of corticomedullary junction and inconspicuous Hassall corpuscles

Differential diagnosis
Diffuse thymic fibrosis

Definition / general
  • Uncommon disorder with no / limited symptoms; may have dyspnea, cough or hemoptysis
  • Area of diffuse fibrosis varies from 3.5 - 17 cm, confined to anterior mediastinum
  • Unknown etiology; altered immunity or infection may play a role
  • Males and females, mean age 48 years

Microscopic (histologic) description
  • Diffuse fibrosis with variable collagen deposition, lymphoplasmacytic infiltrates and involution / atrophy of thymus
  • May show IgG4+ plasma cells and focal obliterative phlebitis (Am J Surg Pathol 2010;34:211)
Ectopic thymus

Definition / general
  • Remnants, implants or accessory nodules that may appear from angle of mandible to thyroid gland, most commonly at level of thyroid gland
  • Rarely becomes hyperplastic or neoplastic

Epidemiology
  • Usually an incidental finding during thyroid surgery in preteens, very rare in adults due to thymic involution

Case reports

Microscopic (histologic) description
  • Normal appearing thymic tissue

Microscopic (histologic) images

Images hosted on other servers:

Central cervical epithelial rest

CK5 / 6, p63, CD10



Differential diagnosis
Ectopic tissue in thymus

Definition / general
  • Usually parathyroid tissue or sebaceous glands, rarely thyroid tissue

Case reports
Mediastinitis, acute

Definition / general
  • Usually in posterior mediastinum, due to traumatic perforation of esophagus or descending infection along prevertebral fascia
  • Initial lesion may be a neck abscess
  • Often causes mediastinal abscess which requires surgical drainage
  • Other causes: chest wall infection or postcardiac surgery, often due to CMV

Case reports

Microscopic (histologic) images

Images hosted on other servers:

Extensive acute inflammation

Fibrinoinflammatory
exudate

Mediastinitis, chronic

Definition / general
  • May compress superior vena cava and simulate malignancy
  • Usually anterior to tracheal bifurcation
  • Some cases may represent fibrosing mediastinitis

Microscopic (histologic) description
  • Granulomas, fibrosis; may be fungus, Histoplasma (with thick fibrous capsule), mycobacteria (thin fibrous capsule)
Thymic dysplasia

Definition / general
  • Congenital thymic alteration due to developmental arrest
  • Lack of differentiation of thymic epithelium, responsible for absence of Hassall corpuscles, is main feature (Histopathology 1992;21:499)

Clinical features
  • Associated with severe combined immunodeficiency syndrome, ataxia telangiectasia, chromosomal instability syndromes, Nezelof syndrome (Arch Pathol Lab Med 1987;111:1118)
  • Incomplete form of DiGeorge syndrome is congenital anomaly with a constellation of findings that includes thymic hypoplasia (J Cutan Pathol 2008;35:380); complete form has absent thymus

Gross description
  • Small thymus (< 5 g)

Microscopic (histologic) description
  • Tubules and rosettes of primitive appearing epithelium without segregation into cortical and medullary regions
  • No Hassall corpuscles, no / rare lymphocytes

Differential diagnosis
Thymic follicular hyperplasia

Definition / general
  • Defined as substantial numbers of lymphoid follicles in thymus of adults
  • Thymus usually has normal size / weight

Clinical features
  • Present in 65% with myasthenia gravis
  • Also associated with hyperthyroidism, Addison disease, SLE, early HIV, multilocular cysts, other immune related diseases
  • Often different clinical history than true thymic hyperplasia (Pathologica 2009;101:175)

Microscopic (histologic) description
  • Follicles with germinal centers, medullary epithelial cells may be disordered or hypertrophied

Differential diagnosis
  • Normal lymphoid follicles of infants / children (few present)
True thymic hyperplasia

Definition / general
  • Thymus larger than normal limits for age, based on tables
  • Otherwise histologically unremarkable

Epidemiology
  • Often in infants or children or in adults after cancer chemotherapy

Case reports

Immunohistochemistry
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