Pseudotumor Deltoideus

Pseudotumor deltoideus refers to bony irregularity or lucency at the deltoid muscle insertion on the proximal humerus. In the appropriate clinical setting, this finding may be mistaken for a neoplastic process. Smooth, well-defined borders and the characteristic location on the lateral aspect of the humerus at the level of deltoid insertion can help steer the diagnosis away from neoplasm.

Cortical thickening may be due to irregularity and slight expansion at the level of the deltoid insertion, while lucency has been suggested to represent a form of a herniation pit. Bone scans may show slightly increased uptake.

The image above shows both cortical irregularity (pink arrow) and a well-defined lucency (white arrow) at the lateral aspect of the humerus at the level of deltoid insertion. CT and PET/CT fusion images show the area of cortical thickening and an intracortical lucency. No increased FDG activity is seen.

References

• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. 8th edition, pages 521-523; Mosby (2004).
• Morgan H, Damron T, Cohen H, Allen M. Pseudotumor deltoideus: a previously undescribed anatomic variant at the deltoid insertion site. Skeletal Radiol. 2001 Sep;30(9):512-8.