Most affected patients are adult males.
Clinical features:
(1) severe coagulopathy, typically Factor 8 or 9 deficiency
(2) an expanding encapsulated hematoma, Normally this is slowly growing but it may undergo a sudden change in size if there is acute hemorrhage into the mass.
(3) there may be a history of trauma at the site prior to its appearance
(4) usually painless at first
Locations affected include the pelvis, lower extremity and upper extremity:
(1) subperiosteal
(2) within bone (osseous) with osteolysis
(3) within skeletal muscle or soft tissue
Complications may include:
(1) a compartment syndrome
(2) nerve compression
(3) pathologic fracture
(4) secondarily infected
(5) rupture with massive hemorrhage
(6) significant disability
(7) a draining fistula
Biopsy or draining of the pseudotumor is contraindicated due to the high rate of complications.
Histologic exam shows:
(1) new and degenerating blood with hemosiderin
(2) a fibrous capsule
Imaging studies may show:
(1) nonspecific masses with patchy calcifications and/or dystrophic calcifications
(2) osseous pseudotumors can destroy the involved bone
(3) subperiosteal pseudotumors may develop an overlying "strut" if the periosteum becomes calcified
(4) avascularity
