Subperiosteal hematoma of the ilium: an unusual complication of acetabular fracture

Clinical History

A 12-year-old female entered the Emergency Department after a fall on the buttock occurred while abducting and externally rotating the right hip. The patient experienced sudden onset of pain in the inguinal region, progressive tenderness in the iliac fossa and gait disturbance. There was no history of bleeding diathesis.

Imaging Findings

No hip fractures were revealed by a plain radiograph on the day of the injury (Fig.1). MRI demonstrated a lens-shaped lesion (maximum diameters: cranio-caudal, 14 cm; antero-posterior, 5.5 cm; latero-lateral, 2.5 cm), with smooth edges, overlying the internal aspect of the right iliac bone and extending homolaterally downward to the anterior wall of the acetabulum. The right iliacus muscle was dislocated medially; the adjacent psoas muscle was not involved. The lesion appeared isointense to skeletal muscle on T1-weighted images and heterogeneously hyperintense on T2-weighted images, being suggestive of a subperiosteal blood collection (Figs.2-3). Concomitantly, the anterior pillar of the right acetabulum presented with intense bone marrow edema, where a thin, hypointense line of fracture was seen (Fig.3c).
The patient was managed conservatively. Forty days after trauma, the subperiosteal hematoma was reduced in size (Fig.4) and the fracture line was not seen anymore. Complete recovery occurred within 6 months of the injury.

Discussion

We report a peculiar case of large subperiosteal iliac hematoma associated to an occult fracture of the anterior pillar of the acetabulum. Subperiosteal hematomas of the ilium are uncommon lesions that specifically occur in children and young adults as a result of a trauma [1-6]. In fact, in young patients the periosteum is loosely attached to the underlying bone and then at risk for traumatic detachment, which is responsible for injury of nutrient vessels and resulting subperiosteal haemorrhage [2]. The anterior pillar is an uncommon site of isolated acetabular fractures in young patients, which include elementary (anterior wall, posterior wall, anterior column, posterior column, and transverse) and combined fractures [7-8].

Clinically, in the acute phase after trauma, subperiosteal hematoma of the ilium is asymptomatic or poorly symptomatic with unspecific discomfort. Gradual worsening with painful limitation of hip motion occurs after a variable delay, usually of a few days [2]. In our case, the concomitant injury of the acetabulum certainly contributed to early development of symptoms such as groin pain and gait disturbance. Subperiosteal haemorrhage may also increase in size and determine neurological symptoms due to impairment of lumbar plexus nerves [3-6], which however were not involved in this case. The hematoma may evolve towards recovery with complete reabsorption, as observed in our patient, or towards progressive ossification [2]. Surgery should be considered if there is a worsening of symptoms or nerve suffering [6]; in our case, since there was no neurological impairment and the acetabular fracture was limited to the trabecular bone with no cortical interruption, conservative therapy was undertaken successfully.

Imaging is essential for diagnosis as well for surgical planning. Both CT and MRI may be helpful but this latter is preferable in young patients, as it does not use ionizing radiations. In acute and subacute phases after injury, a subperiosteal hematoma of the ilium is strongly suggested by a lens-shaped lesion confined between the internal aspect of the iliac bone, on the lateral side, and the iliacus muscle, on the medial side [2]. Importantly, since subperiosteal iliac hematoma may be poorly symptomatic, it may be undiagnosed in patients with no history of major trauma and incidentally discovered as a chronic ossified lesion in adulthood [9].

In conclusion, subperiosteal iliac hematoma should be suspected in young patients presenting with a history of recent hip trauma and poor or unspecific symptoms. MRI ensures optimal diagnosis and allows identifying concomitant injuries such as occult fractures.

Differential Diagnosis List

Final Diagnosis

Subperiosteal iliac hematoma and trabecular fracture of the acetabulum

URL:	https://www.eurorad.org/case/14182
DOI:	10.1594/EURORAD/CASE.14182
ISSN:	1563-4086