Infantile fibrosarcoma

Infantile fibrosarcomas also known as congenital fibrosarcoma, infantile fibrosarcoma-like tumor, and cellular congenital mesoblastic nephroma are locally aggressive rarely metastasizing fibroblastic tumors found in the pediatric population.

Epidemiology

Infantile fibrosarcomas are most commonly found in the first two years of life with more than 75% of the cases found during the first year and at birth and a further 15% in the second year of life ¹. A bit less than 15% are already detected at prenatal ultrasound ^1-3.

Associations

There is a relation to congenital mesoblastic nephroma ¹.

Diagnosis

The diagnosis of infantile fibrosarcomas is based on patient age, histology and molecular pathology ¹.

Diagnostic criteria

Diagnostic criteria of infantile fibrosarcoma according to the WHO classification of tumors: soft tissue and bone (5^th edition) ¹:

• age <2 years in the majority of patients
• usually herringbone or fascicular growth pattern with intersecting bundles of spindled to ovoid or round cells
• mixed inflammatory changes and hemangiopericytoma-like staghorn vasculature

The following genetic criterion is desirable:

• ETV6-NTRK3 fusion or rearrangements of the NTRK1, BRAF and MET genes

Clinical presentation

The typical manifestation is a rapidly growing painless mass or nodule, they may look like a vascular tumor and ulcerate ¹.

Pathology

Infantile fibrosarcomas are locally aggressive tumors characterized by spindle cells or primitive ovoid cells often growing in a fascicular or herringbone architecture with a staghorn vascular pattern, mixed inflammatory changes and ^1,2.

Location

Infantile fibrosarcomas are usually found in the superficial and deep soft tissues of the following locations ^1-5:

• extremities
• trunk
• head and neck region

Less commonly it is found in the abdomen or retroperitoneum and rarely it involves the bones and viscera such as the lung and the bowel ¹.

Macroscopic appearance

Macroscopically infantile fibrosarcomas usually appear as poorly circumscribed lobulated tumors with infiltrative boundaries, some feature a pseudocapsule. They can be quite large when discovered. ¹.

Microscopic appearance

The microscopic spectrum of infantile fibrosarcoma is broad and includes the following ^1,2:

• monomorphic spindle cells to ovoid/round cells
• fascicular growth in a ‘herringbone’ architecture
• collagenous or myxoid background
• hemangiopericytoma-like vascular pattern
• mixed chronic inflammatory infiltrates
• variable mitotic activity
• frequently zonal necrosis and/or hemorrhages

Immunophenotype

Immunohistochemistry stains are non-specific and can display expressions of SMA, CD34, S100 or desmin ¹.

Genetics

Infantile fibrosarcoma often displays an ETV6-NTRK3 gene fusion or rearrangement ^{12, 4}.

Radiographic features

Imaging findings usually reveal a nonspecific heterogeneous mass with signs of intralesional hemorrhage ¹.

Ultrasound

Ultrasound usually reveals a heterogeneous isoechoic, hypervascular mass with dilated vessels sometimes looking a bit like hemangioma ^2,4.

MRI

On MRI infantile fibrosarcomas are heterogeneous soft tissue masses and can show well-defined or infiltrative tumor margins. They might show low signal intensity fibrous streaks ². They might show intralesional signal voids due to vasculature and hemorrhagic components, being hyperintense in both T1-weighted and T2-weighted images ^2,4-7.

Signal characteristics are usually as follows:

• T1: generally hypo- to isointense to muscle
• T2: generally hyperintense signal intensity
• T1 C+ (Gd): heterogeneous predominantly peripheral enhancement

Radiology report

The radiological report should include a description of the following:

• form, location and size
• tumor margins
• relation to the muscular fascia
• relationship to local nerves and vessels
• relations to other organs

Treatment and prognosis

Treatment options include combinations of surgery with wide local excision being the surgical treatment of choice and chemotherapy ^3,8. Local recurrence occurs in up to 40% and is especially associated with incomplete resection. Metastases occur rarely and most often affect the lungs. The 10-year survival is about 90% with standard therapy ^1-3.

History and etymology

History and early descriptions of congenital infantile fibrosarcoma are very vague.

According to the Mexican physician and pediatric pathologist, Francisco González Crussí several mesenchymal tumors were reported in the literature up to 1940 and called fibrosarcoma ^9,10 with the caveat that the nomenclature was too confusing and the illustrations too inaccurate to be sure of the diagnosis ⁹.

Differential diagnosis

Conditions that can mimic the presentation and/or the appearance of infantile fibrosarcoma include ^1-4:

• adult fibrosarcoma
• infantile fibromatosis
• myofibromatosis