Weekly Case

Title : Case 658

Age / Sex : 46 / M

Chief complaint: left flank pain developed 10 days ago

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : 강창호 (Chang Ho Kang), 고려대학교 안암병원 (Korea University Anam Hospital)


Side strain (internal oblique muscle tear)


additional Hx: Start taking table tennis lessons from a few months ago


Initial CT showed a peripherally enhancing low attenuation mass in the left-sided internal oblique muscle. Mass increased on F/U CT and subsequently decreased which was demonstrated by MR images (not shown). US exam for biopsy was requested but biopsy not performed because US findings were more likely to be muscle strain rather than neoplastic conditions. Last F/U US well demonstrated healing process of the muscle strain.


Differential Diagnosis:

Muscle strain



Characterized by sudden onset of pain and point tenderness.

Activities associated with cricket, javelin throwing, rowing, ice hockey, and tennis.

Commonly occurs at rib or costal cartilage insertion site.


Superficial anterolateral abdominal muscle & Located beneath external oblique muscle.
Origin: inguinal ligament, Iliac crest, lumbodorsal fascia.

Insertion: linea alba, pectineal line of pubis (via conjoint tendon), ribs 10-12th.


Accessory muscle of respiration, antagonist to diaphragm.
Rotation, side-bending, with external oblique muscle of opposite side.

  • Left internal oblique & right external oblique contracts.

  • Torso flexes and rotates to bring right shoulder towards left hip.

Injury mechanism

Sudden eccentric contracture cause rupture.

Activities associated with lengthening of muscle (In hyperextended position).

Sudden vigorous motion of contraction or pull thorough.
Image findings

Acute tear: edema/hemorrhage or hematoma tracking between myofascial coverings of internal & oblique muscles.

Stripping of periosteum from undersurface of rib.

At F/U, gap created by detachment of muscle fibers filled with fibrosis and scar tissue which could be appeared as hypertrophied mass.

Take home message

In severe lateral abdominal pain following trunk rotation, tear of abdominal oblique muscles could be considered as a differential diagnosis.



  1. David A. Connel et al. Side Strain: A Tear of Internal Oblique Musculature. AJR 2003; 181:1511-1517.

  2. Kazuki Asai et al. Internal Oblique Muscle Strain on the Side of the Dominant Arm in a Representative Handball Player. Curr Sports Med Rep. 2019; 18(10):358-360. 

  3. Myles Murphy et al. Acute Tearing of the Oblique Abdominal Wall Insertion Onto The Iliac Crest In An Australian Football Player: A Case Report. Int J Sports Phys Ther. 2016; 11(7):1125-1134.

  4. Shanna A. Matalon et al. Don’t Forget the Abdominal Wall: Imaging Spectrum of Abdominal Wall Injuries after Nonpenetrating Trauma. RadioGraphics 2017; 37:1218-1235.


Correct Answer
Total applicants 22 Correct answers 4
Name Institution
김기욱 국군수도병원, 전문의
한유비 전문의
이규정 고대안암병원, 전문의
강지희 서울대학교병원, 전문의