Acute abdominal pain is a common complaint in children. We came across several unusual causes of acute abdomen including jejunal haematoma, perforation and abdominal abscess following hydrostatic intussusception reduction, twisting of mesenteric cyst, perforation of sigmoid colon and Meckel\'s diverticulum presenting with intussusception. In this article, we aim to present imaging features of these entities so that paediatric surgeons, radiologists and other health-care providers are aware of these unusual manifestations of acute abdomen.

BACKGROUND: Myositis ossificans circumscripta is a self-limiting, benign, ossifying lesion that can affect any type of soft tissue. It is most commonly found in muscles as a solitary lesion. A history of recent trauma has been reported in approximately 50% of cases. Clinically, MOC presents as a painful swelling, which rapidly increases in size. The pain and inflammatory symptoms spontaneously disappear after approximately 2-6 weeks, and the mass stabilizes or decreases. Radiologically, myositis ossificans circumscripta can be divided into two phases. The first is the acute phase, which is followed by the mature phase 2-6 weeks later. During the acute phase, the radiological aspect does not show any specific abnormality. In the mature phase, plain radiographs and computed tomography show blurred calcifications around a hypodense center. We describe here the first case of myositis ossificans circumscripta, with appropriate follow-up, occurring during sunitinib exposure.
METHODS: We report a case of myositis ossificans circumscripta in a 34-year-old man (ethnicity unknown) receiving sunitinib for metastatic alveolar soft part sarcoma of the left thigh after surgery and radiotherapy. Four months after the first dose of sunitinib, the patient experienced painful swelling in the surgical scar area. Magnetic resonance imaging showed diffuse and marked edema of the anterior compartment of the thigh, without nodular lesions circumscribing a central core, and without bone signal abnormality. The increased visibility of the intermuscular fascia and convergence of normal muscle fibers (black hole effect), without the displacement seen in tumors, were suggestive of myositis. Therefore, antiangiogenic treatment was discontinued, and the symptoms rapidly resolved within a few days. Three weeks after the discontinuation of sunitinib, the inflammatory findings completely disappeared. Two months after the diagnosis of myositis ossificans circumscripta, plain radiographs and computed tomography showed an extensive calcified mass measuring > 12 cm. The continuation of favorable clinical outcomes was confirmed.
CONCLUSIONS: To the best of our knowledge, this is the first case of myositis ossificans circumscripta with appropriate follow-up occurring during sunitinib exposure. Owing to multimodal treatment of sarcoma, we cannot rule out the radiotherapy and surgery causality.

A brown tumor is one of the manifestations of hyperparathyroidism. It is a rare type of bone lesion that most often occurs in mandible, ribs, and large bones. Spinal involvement is extremely rare. We report an unusual case of a brown tumor of the axis vertebra in a 33-year-old male who presented to the orthopaedic clinic with posttraumatic C2 vertebra fracture and myelopathy. To plan further fixation and stabilization of C2 fracture, the patient underwent a plain radiograph and magnetic resonance imaging (MRI) of the cervical spine. The available routine chest radiograph at the time of MRI reporting clinched the diagnosis of primary hyperparathyroidism with a brown tumor of the axis vertebra. Thus, familiarity with subtle radiographic findings of this condition not only led to early diagnosis and appropriate treatment but also avoided unnecessary C2 biopsy and hardware fixation.