Thymushyperplasie bei Morbus Basedow
Thymushyperplasie bei Morbus Basedow
Thymushyperplasie Radiopaedia • CC-by-nc-sa 3.0 • de
Thymic hyperplasia is a disorder whereby there is hyperplasia of the thymus gland.
Pathology
Thymus hyperplasia can be subdivided into two forms:
Both true thymic hyperplasia and lymphoid hyperplasia manifest as diffuse symmetric enlargement of the thymus so that it is difficult to distinguish between the two types on the basis of imaging findings alone.
It is important that radiologists be able to distinguish thymic hyperplasia from neoplasm, which tends to present as a focal mass.
True thymic hyperplasia
True thymic hyperplasia associations include:
- rebound hyperplasia to chemotherapy/steroids (see: thymic rebound hyperplasia)
- radiation therapy
- burns
- other severe systemic stresses
Lymphoid hyperplasia
This is also known as lymphoid follicular thymic hyperplasia or autoimmune thymitis. Lymphoid hyperplasia associations include
Radiographic features
Diffuse symmetric enlargement of the gland is the key morphologic feature of hyperplasia (neoplasm tends to manifest as a focal mass).
MRI
Chemical shift artifact may be useful in differentiating from other tumors :
- chemical shift MRI helps differentiate thymic hyperplasia and thymus gland tumors in patients 16 years of age or older
- chemical shift MRI depicts no decrease in signal intensity of thymic tumors, unlike the decreased signal intensity of thymic hyperplasia
- this can be formally calculated using the chemical shift ratio (CSR)
Differentiating normal from hyperplastic thymus can be difficult and guidelines for making this distinction and verifying the presence of normal thymus include :
- presence of rounded soft-tissue masses 7 mm
- presence of a convex contour of the thymus beyond 19 years of age
- presence of soft-tissue lobulation
- presence of increased thymic thickness (should be ≤1.3 cm beyond age 20 years)
- presence of a diagnosis associated with thymic enlargement or hyperplasia, e.g. Graves disease
Nuclear medicine
FDG PET is often performed in patients with malignancy; however, differentiation between thymic hyperplasia and thymic involvement by malignancy is difficult because the thymus demonstrates normal physiologic uptake.
Morbus Basedow Radiopaedia • CC-by-nc-sa 3.0 • de
Graves disease (also known as Basedow disease in mainland Europe) is an autoimmune thyroid disease and is the most common cause of thyrotoxicosis (up to 85%).
Epidemiology
There is a strong female predilection with an F:M ratio of at least 5:1. It typically presents in middle age.
Clinical presentation
Patients are thyrotoxic. Extrathyroidal manifestations include:
- cutaneous manifestations of Graves disease
- thyroid dermopathy (formerly called pretibial myxedema): occurs in ~2% and almost always associated with thyroid ophthalmopathy
- skeletal manifestations of Graves disease
- thyroid acropachy: occurs in ~1%
- Graves ophthalmopathy (orbitopathy): affects 20-25% of cases
- encephalopathy associated with autoimmune thyroid disease (EAATD)
- much more commonly associated with Hashimoto thyroiditis
The combination of exophthalmos, palpitations, and goiter is called the Merseburger (or Merseburg) triad.
Pathology
Results from an antibody directed stimulation of the thyroid-stimulating hormone (TSH) receptor, with resultant production and release of T3 and T4.
Macroscopic appearance
The affected gland shows diffuse, symmetrical enlargement, with a fleshy red cut surface. This appearance can be altered by preoperative treatment or chronicity.
Microscopic appearance
The histological features are consistent with the activated state of the gland:
- plump follicular cells with increased amounts of eosinophilic cytoplasm
- hyperplastic follicles with papillary epithelial infoldings
- evidence of colloid reabsorption including 'scalloping' at the apical membrane and variable follicle collapse and exhaustion
These features can be altered by preoperative treatment or chronicity.
Serology
- TSH: suppressed
- T4: elevated
- T3: elevated
- TSH receptor antibodies (TSI, TGI, TBII): positive
Radiographic features
Ultrasound
- thyroid gland is often enlarged and hypoechogenic, can be hyperechoic
- heterogeneous thyroid echotexture
- relative absence of nodularity in uncomplicated cases
- hypervascular; may demonstrate a thyroid inferno pattern on color Doppler
Nuclear medicine
- iodine-123: imaging performed at around 2-6 days; classically demonstrates homogeneously increased activity in an enlarged gland
- technetium-99m pertechnetate: homogeneously increased activity in an enlarged thyroid gland
History and etymology
It is named after Robert James Graves (1796-1852), Irish surgeon, who first described it in 1835 , and Carl Adolph von Basedow (1799-1854), German physician, who described it in 1840 . The Merseburger triad was first described by Basedow who practiced in Merseburg .
Differential diagnosis
For hyperthyroidism consider:
- Marine-Lenhart syndrome
- toxic thyroid adenoma
- toxic multinodular goiter
- inflammatory:
- pituitary adenoma
- extrathyroid origin
- struma ovarii
- metastatic thyroid carcinoma
- factitious hyperthyroidism
Practical points
- patients with Graves disease are at higher risk of iodinated contrast media-induced thyrotoxicosis
Siehe auch:
Assoziationen und Differentialdiagnosen zu Thymushyperplasie bei Morbus Basedow:
