Case presentation
A 7-year-old male presented to the Uganda cancer institute with a history of slowly progressive painless abdominal mass in the left hypochondria region. The mass had lasted for three years and was associated with a history of weight loss and drenching night sweats. There was no history of allergy or developmental abnormalities.
On general examination he looked ill, mild pallor, however; not jaundiced, not febrile.
On physical examination, there was an irregular hard and non-tender mass measuring13x14cm. It was mobile and not attached to the underlying structures but attached to the underlying skin (Figure 1). There were no palpable regional lymph nodes or organomegaly.
Routine biochemical and hematological (Hb value 10g/dl, WBC: 9,000/mm3) investigations were carried out and were all within normal limits.
An abdominal ultrasound scan showed a subcutaneous solid mass in the left hypochondriac that was predominantly hypoechoic that measured 7cm by 4cm with acoustic shadowing in some areas. There was an increased flow on color Doppler. (Figure 2)
Computed tomography (CT) of the abdomen demonstrated a large micro-lobulated calcified hyperdense mass that measured 8cm×7cmx4cm in the left external oblique muscle abutting but not infiltrating the internal oblique muscle. The rest of the abdominal organs appear normal. There were no enlarged mesenteric lymph nodes (Figure 3).
Under ultrasound guidance, trucut biopsies were taken and the sample was sent for histopathological evaluation. The hematoxylin and eosin-stained sections showed tissue composed of mature bone trabeculae, fibrous tissue, and muscle with foci of calcifications without malignant cells, which were features of MO (Figure 4). The mass was removed by surgical excision and no immediate or late complications were seen. There was no recurrence in a one-year follow-up.