Characteristic MR image finding of squatting exercise-induced rhabdomyolysis of the thigh muscles

Abstract

Objective: To describe the characteristic MRI appearance of squatting-induced rhabdomyolysis involving the thigh muscles.

Methods: This study consisted of 10 cases obtained at 3 institutions from 2005 to 2015. A retrospective review was performed to obtain clinical information and MR scans for rhabdomyolysis of the thigh muscles. MRI was analyzed according to the distribution and degree of muscle involvement; the degree was assessed and graded as normal, mild or prominent.

Results: The mean patient age was 20.2 years (range, 15-24 years), and 7 of the 10 patients were male. All patients had history of excessive squatting action, suffered clinically from bilateral thigh pain and were confirmed to have rhabdomyolysis through analysis of serum creatine kinase (CK) levels. All of the patients (10/10) exhibited diffuse mild to prominent degree involvement of the anterior thigh muscles according to fluid-sensitive MR sequences. Among the anterior thigh muscles, the rectus femoris was spared in 8 patients (8/10) and mild degree involved in 2 patients (2/10). Thus, no cases exhibited prominent degree involvement of the rectus femoris muscle.

Conclusion: Preservation of the rectus femoris muscle on MRI in squatting-induced rhabdomyolysis may be useful for differentiating rhabdomyolysis from other aetiologies. Advances in knowledge: Preservation of rectus femoris on MRI is distinguishable finding in squatting-induced rhabdomyolysis and reflects the functional anatomy of anterior thigh muscles.

Figure 1.

A 15-year-old female with bilateral thigh pain and dark urine 3 days after an episode of squatting exercise performed over 200 times. (a) Axial T₁ weighted image showing homogenously intermediate to low signal intensity involving the right quadriceps femoris muscles. (b) Axial T₂ weighted image showing diffusely increased signal intensities involving the vastus lateralis, medius and intermedius muscles sparing of the rectus femoris. (c) Axial fat-suppressed T₂ weighted image demonstrating diffusely increased signal intensities involving the quadriceps femoris (grade 1) except the rectus femoris. (d) Axial fat-suppressed T₂ weighted image showing spared rectus femoris and symmetry with the right thigh. RF, rectus femoris; VI, vastus intermedius; VL, vastus lateralis; VM, vastus medialis.

Figure 2.

A 20-year-old female with bilateral thigh pain and dark urine 2 days after an episode of squatting exercise performed over 200 times. (a) Axial T₁ weighted image showing homogenously intermediate to low signal intensities involving left quadriceps femoris muscles. (b) Axial T₂ weighted image showing diffusely increased signal intensities involving the vastus lateralis, medius and intermedius muscles and mildly increased signal intensity at the rectus femoris muscle (grade 1). There is subfascial fluid collection and adjacent subcutaneous oedema. (c) Axial fat-suppressed T₂ weighted image demonstrating diffuse involvement of the vastus lateralis, medialis and intermedius muscles (grade 2) and mild involvement of the rectus femoris muscle (grade 1).

Figure 3.

A 16-year-old male with bilateral thigh pain and dark urine after an episode of squatting exercise performed over 150 times. (a) Axial T₁ weighted image showing homogenously intermediate to low signal intensities involving the right quadriceps femoris muscles. (b) Axial T₂ weighted image showing diffusely increased signal intensities involving the quadriceps femoris except the rectus femoris, with mildly increased signal intensity at the adductor muscle (arrow). (c) Axial fat-suppressed T₂ weighted image demonstrating diffuse involvement of the quadriceps femoris (grade 1) with a spared rectus femoris and mild involvement of the adductor muscle (grade 1, arrow).

Figure 4.

A 15-year-old female with bilateral thigh pain and dark urine after performing squatting exercise over 170 times. (a–c) Images taken 4 days after exercise, and (d) image taken on follow-up 7 weeks later. (a) Axial T₁ weighted image showing homogenously intermediate to low signal intensities involving the right quadriceps femoris muscles. (b) Axial T₂ weighted image showing diffusely increased signal intensities involving the quadriceps femoris (grade 1) except the rectus femoris. (c) Axial Gd-enhanced T₁ weighted image with fat suppression demonstrating diffusely homogeneous enhancement of the anterior thigh muscle with sparing of the rectus femoris and without evidence of myonecrosis. (d) Follow-up images showing the improved state of anterior thigh muscle swelling and return to normal signal intensity in Gd-enhanced T₁ weighted images.