Thymic hyperplasia due to excess growth hormone stimulation: A case report

Abstract

Growth hormone has a strong role in stimulation of the thymus. We report a case of thymic hyperplasia due to excess endogenous growth hormone in the setting of acromegaly. Acromegaly often presents with systemic manifestations that may be confused with a systemic hematologic malignancy or infection, especially if an anterior mediastinal mass is present but unrecognized as a benign thymic hyperplasia. It is important for radiologists to be aware of this association between growth hormone and thymic stimulation because it may increase confidence diagnosing thymic hyperplasia in this setting, and avoid unnecessary mediastinal biopsy or surgery.

Keywords: Acromegaly; Growth hormone; Pituitary adenoma; Thymic hyperplasia.

Fig. 1

(A) Contrast-enhanced CT of the chest at the time of presentation showed an anterior mediastinal mass (white arrow), initially read as possible lymphoma or thymic mass at outside hospital. (B) Contrast-enhanced CT of the chest performed 4 months following resection of the GH-secreting pituitary macroadenoma showed decreased size of this triangular-shaped well-demarcated anterior mediastinal mass (white arrow), consistent with decreasing thymic hyperplasia.

Fig. 2

(A) Coronal T2-weighted and (B) sagittal post-contrast T1-weight imaging of the brain showed a 2 cm sellar mass with suprasellar extension, consistent with a pituitary macroadenoma.

Fig. 3

(A) Axial and (B) coronal cinematic rendered CT show triangular shaped anterior mediastinal mass (white arrow) with smooth contours and internal architecture consistent with thymic hyperplasia. The additional detail provided by the cinematic rendering provides depth perception to visualize the internal architecture as well as excellent definition of adjacent vascular and pulmonary anatomy.

Fig. 4

Axial dual-echo imaging shows clear signal drop-out in the anterior mediastinal mass (white arrow) from the (A) in-phase image to the (B) out-of-phase image. Calculated Signal Intensity Index using ROIs placed in the mass was 67%, consistent with thymic hyperplasia.