Thymic Hyperplasia



Thymic Hyperplasia


Borislav A. Alexiev, M.D.

Allen P. Burke, M.D.



Terminology

Most thymic hyperplasia is the result of reactive lymphoid hyperplasia, frequently in the setting of autoimmune disease, notably myasthenia gravis. Reactive thymic hyperplasia has also been described with other abnormalities, especially Graves disease,1,2 sarcoidosis,3 Castleman disease,4 and Beckwith-Wiedemann syndrome5 (Table 114.1). Reactive thymic hyperplasia may also occur in patients without known autoimmune disease.11

True thymic hyperplasia is defined as an increase in size and weight of the thymus gland, which by definition maintains a normal histologic architecture. True thymic hyperplasia without any other disease (idiopathic) is a rare disorder, with only a handful of well-documented examples in the literature.5








TABLE 114.1 Conditions Associated with Thymic Hyperplasia







  • Myasthenia gravis



  • Graves disease



  • Castleman disease4



  • Beckwith-Wiedemann syndrome5



  • Sjögren syndrome6



  • Celiac disease7



  • Antiphospholipid syndrome8



  • Systemic sclerosis9



  • Multiple sclerosis10



  • Autoimmune hemolytic anemia10



  • Systemic lupus erythematosus10



  • Ulcerative colitis10



  • Sarcoidosis3


The normal range of thymic mass is age dependent.12,13 In general, any weight over 15 g is abnormal in older adults, and a weight over 35 g is abnormal in children and young adults. When the weight exceeds 100 g, the term “massive” thymic hyperplasia is used.

Enlargement of the thymus gland may occur as a rebound phenomenon after recovery from severe stress, after administration of steroids, and after treatment of malignant tumors14,15,16 (Table 114.2).


Gross Pathology

In cases of true thymic hyperplasia, the thymus is massively and uniformly enlarged, and the parenchyma is whitish-yellow with hemorrhagic areas.17 In cases of reactive thymic hyperplasia, there are no discerning gross features, although the presence of cysts, firm areas, and necrosis should be documented and sampled, to rule out malignancy. It is also recommended to weigh the gland, in addition to providing standard measurements.


Microscopic Pathology

In true thymic hyperplasia, histologic examination reveals a normal thymic architecture with well-defined cortical and medullary areas (Fig. 114.1).17,18,19,20 In the cortical areas, macrophages with phagocytized nuclear debris (starry sky macrophages) could be observed, suggesting acute cortical involution. Other types of involutional change observed in infants (lymphocyte depletion) are not seen.21









TABLE 114.2 Differential Diagnosis of Thymic Hyperplasia and Mimickers

Incidence

Associations

Pathology Findings


True thymic hyperplasia

Rare

None, usually children

Normal architecture, including Hassall corpuscles, degenerative changes of hemorrhage, vascular proliferation


Reactive thymic hyperplasia

Common

Autoimmune disorders (see Table 114.1)

B-cell follicular hyperplasia with follicular dendritic cells and germinal centers


B-cell-rich thymoma

Uncommon

Myasthenia gravis

Thymus-like expansion of neoplastic epithelial cells admixed with immature T cells, replacing normal architecture


Micronodular thymoma

Rare

Myasthenia gravis (uncommon)

Thymoma with large areas of reactive B-cell follicles


Rebound thymic hyperplasia

Rare

Chemotherapy, stress

Few reports; normal thymic architecture with increased size

Only gold members can continue reading. Log In or Register to continue

Related posts:

  1. Pediatric Interstitial Lung Disease and Hermansky-Pudlak Syndrome
  2. Pulmonary Capillaritis
  3. Small Cell Carcinoma
  4. Lymphoepithelioma-Like Carcinoma

Stay updated, free articles. Join our Telegram channel
Tags:
Aug 19, 2016 | Posted by in CARDIOLOGY | Comments Off on Thymic Hyperplasia

Full access? Get Clinical Tree
Get Clinical Tree app for offline access