Infantile Fibromatosis
Differential Diagnosis
Applies to immature / diffuse / mesenchymal type
(for differential diagnosis of adult type see extra-abdominal desmoid fibromatosis)
- Infantile fibrosarcoma
- Fibrous hamartoma of infancy
- Inflammatory myofibroblastic tumor
- Lipoblastomatosis
- Myxoid liposarcoma
- Embryonal rhabdomyosarcoma
- Inclusion body fibromatosis
| Infantile Fibromatosis | Infantile Fibrosarcoma |
|---|---|
| Mild to moderate cellularity | Usually more cellular |
| Fine chromatin | Usually clumped chromatin |
| Rarely > 5 mitotic figures per HPF | Usually > 5 mitotic figures per HPF |
| Atypical mitotic figures rare | Atypical mitotic figures common |
| Variably collagenous stroma | Little collagen in stroma |
| No herringbone pattern | Frequent herringbone pattern |
| Hemorrhage and necrosis rare | Frequent hemorrhage and necrosis |
| Muscle fibers preserved | Muscle fibers destroyed |
| Lacks t(12;15) | t(12;15) in most cases |
| Fibrous Hamartoma of Infancy | Infantile Fibromatosis |
|---|---|
| Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells | Not triphasic |
| Primarily superficial | Usually centered on muscle |
| Inflammatory Myofibroblastic Tumor | Infantile Fibromatosis |
|---|---|
| Frequent in abdomen | Rare in abdomen |
| Usually age 0-14 years | Age <5 years |
| Prominent inflammation | Variable, peripheral inflammation |
| Variable locations | Centered in muscle |
| Lipoblastomatosis | Infantile Fibromatosis |
|---|---|
| At least focal plexiform capillaries | No plexiform capillaries |
| Contains lipoblasts | Mature fat cells only |
| Lobular pattern | Infiltrative pattern |
| Myxoid Liposarcoma | Infantile Fibromatosis |
|---|---|
| Chicken-wire vascular pattern | No chicken-wire pattern |
| Contains lipoblasts | Mature fat cells only |
| Essentially does not occur <5 years of age | <5 years of age |
| Embryonal Rhabdomyosarcoma | Infantile Fibromatosis |
|---|---|
| Rarely involves skeletal muscle | Usually centered on skeletal muscle |
| Cytologically atypical | Cytologically bland |
| No fat component | Fat frequently part of lesion |
| MyoD1 positive | MyoD1 negative |
| Desmin positive | Desmin variable |
| Infantile Fibromatosis | Inclusion Body Fibromatosis |
|---|---|
| Rare in hand | Vast majority in hands or feet |
| Usually >2 cm | Rarely >2 cm |
| Involves skeletal muscle | Muscle not involved |
| No inclusions | Inclusions usually present |
