Teaching Case

This 8-year-old girl presented to paediatric outpatient clinic after her mother noticed a mass within the central abdomen. There were no further symptoms.
Clinical examination confirmed the presence of a painless firm mass extending from the pelvis to above the umblicus. Alpha fetoprotein and HCG were normal.

Ultrasound abdomen identified a huge mass (> 20cm) within the abdomen, commencing immediately above the dome of the bladder, extending into the upper abdomen to the level of the pancreas. The mass extended from the anterior peritoneum, posteriorly to the pre-vertebral region, with a prominently midline/right paramidline position. Adjacent structures were displaced rather than invaded. All the solid organs were normal.

CT confirmed a hugh peritoneal mass, with prominent perilesional and intralesional vascularity. The superior mesenteric vein was enlarged with multiple collateral vessels in the upper abdomen and right paracolic gutter. No distant disease identified.

Although amenable to ultrasound guided biopsy a joint clinicoradiological decision was made, that open biopsy should be performed. This confirmed a vascular mass with necrotic components and haemorrhagic free fluid.

Rhabdomyosarcoma is the commonest soft tissue tumour in the paediatric population. Rhabodomyosarcomas are derived from primitive muscle cells and can occur in any part of the body from the orbits to muscular extremities and are highly malignant in nature. The incidence is 6 cases per 1,000,000 population per year in children and adolescents younger than 15 years.

Several distinct histologic groups are described which have important prognostic significance. These include: embryonal rhabdomyosarcoma (ERMS) (55%) the botryoid variant of ERMS (5%), alveolar rhabdomyosarcoma (ARMS) (20%) and undifferentiated sarcoma (UDS) (20%) [1]. Alveolar rhabdomyosarcoma is more common in adolescents, whereas embryonal type is commoner in younger children. Thirty nine (39%) of alveolar rhabdomyosarcomas present with distant disease, in contrast to embryonal (25%) [2].

First line imaging is usually ultrasound abdomen, identifying a heterogenous, often well vascularised mass within the abdominal cavity, separate from the solid organs. It may have areas of cavitation within. This typically displaces rather than invades adjacent structures. Cross sectional imaging is then merited - typically CT in the first instance, to further delineate the extent of the mass and to assess for locoregional and metastatic disease, which is common. Liver, bone, lungs and lymph nodes are all common sites for metastases. Recent studies have attempted to identify whether cross sectional imaging can distinguish sub-types of rhabdomyosarcoma, but the outcome was negative [3].

Treatment of patients with rhabdomyosarcoma involves a combination of surgery, chemotherapy, and radiation therapy. Although all patients require chemotherapy, regimens vary depending on the tumour stage and type. Surgical management varies depending on the location of the tumour, but if feasible tumours should be removed promptly. Even if metastatic disease is present, surgical excision of the primary site is recommended, but local recurrence is common.

The prognosis for all forms of rhabdomyosarcoma is poor, with differences between subgroups, the embryonal type having the most favourable prognosis. Overall mortality is closely related to the age of the patient and site of the tumour, with 5-year survival highest in children aged 1-4 years (77%) and worst in infants (47%) and adolescent (48%) [4].

For abdominal mass in paediatric population, if all the solid organs are identified on ultrasound and are normal, consider a rhabdomyosarcoma.

In the paediatric population be cautious with percutaneous image guided biopsy even if technically feasible.