Inflammatory Myofibroblastic Tumor

Differential Diagnosis

Sclerosing Inflammatory Lesions (Retroperitonitis, Mesenteritis, Mediastinitis, Cholangitis, Pancreatitis)	Inflammatory Myofibroblastic Tumor
Diffuse, typically no distinct mass	Circumscribed mass lesion
Rare in children	Usually in children
IgG4 serum levels and plasma cells increased	No association with IgG4

Inflammatory Myofibroblastic Tumor	Nodular Fasciitis
Frequently over 5 cm	Rarely over 5 cm
Usually in children	Rare in children
Frequently involves abdominal cavity	Does not involve abdominal cavity
Variable patterns	Usually loose pattern throughout
Prominent inflammatory cells	Only scattered inflammatory cells

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

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic	Inflammatory Myofibroblastic Tumor
Rare <12 years of age	Age usually <14, rare >30
Inflammation not prominent	Prominent inflammation, particularly plasma cells
Alk1 negative	Alk1 frequently positive
Beta catenin 80-90%	Beta catenin negative

Inflammatory Myofibroblastic Tumor	Gastrointestinal Stromal Tumor
Usually in children	Rare in children
Frequently associated with systemic signs and symptoms	Not associated with systemic signs and symptoms
Prominent inflammatory cells	Usually only scattered inflammatory cells
Frequently positive for desmin, keratin and ALK	Desmin, keratin and ALK negative
CD117, DOG1, CD34 negative	CD117 74-95%, DOG1 87-95%, CD34 70%

Inflammatory Fibroid Polyp	Inflammatory Myofibroblastic Tumor
Systemic signs and symptoms absent	Systemic signs and symptoms frequent
Infrequent involvement of muscularis propria	Frequent involvement of muscularis propria
Eosinophils predominate	Plasma cells usually predominate
Concentric onion skin like pattern around vessels and glands is frequent	Lacks concentric onion skin pattern
Not associated with lymphadenopathy	May have reactive regional lymphadenopathy

Inflammatory Myofibroblastic Tumor	Leiomyosarcoma of Soft Tissue
Usually <14 years, rare >30 years	Rare under 12 years
Chronic inflammation usual	Infrequent inflammation

Rare inflammatory leiomyosarcoma exhibits a regular fascicular pattern

Inflammatory Malignant Fibrous Histiocytoma	Inflammatory Myofibroblastic Tumor
Mean age 50, wide range	Usually <14 years, rare >30 years
Sheets of neutrophils	Mixed or lymphocyte predominant inflammation
Marked cytologic atypia	Absent or mild atypia

Myofibroma	Inflammatory Myofibroblastic Tumor
90% <2 years	Usually age 0-14 years
Biphasic nodules with immature cells	No immature cells
Hemangiopericytomatous vessels	No HPC like vessels
Rare in abdomen	Frequent in abdomen

Dedifferentiated Liposarcoma	Inflammatory Myofibroblastic Tumor
High grade nonlipogenic comoponent present	Lacks significant cytologic atypia
Atypical lipomatous tumor component present	Lacks lipomatous component

Inflammatory Myofibroblastic Tumor	Inflammatory Pseudotumor of Lymph Node and Spleen
ALK positive 35-60%	ALK negative
EBV negative	EBV may be positive
Rare in lymph node and spleen	Occurs in lymph node and spleen

In the GU tract some consider the following to be separate entities while others consider them to be the same lesion

Inflammatory Myofibroblastic Tumor	Pseudosarcomatous Myofibroblastic Proliferation of GU Tract
Prominent lymphoplasmacytic infiltrate	Lacks prominent plasma cells
Frequent storiform and fibrous areas	Lacks storiform and fibrous areas
Pale eosinophilic cytoplasm on spindle cells	Intensely eosinophilic cytoplasm on spindle cells

Both may be postive for actin, desmin, keratin, ALK and both are benign at this site

Inflammatory Myofibroblastic Tumor	Follicular Dendritic Cell Neoplasm
Rarely involves lymph node or spleen	Frequently involves lymph node and spleen
ALK positive 35-60%	ALK negative
CD21, CD23, CD35 negative	CD21, CD23 or CD35 positive
EBV negative	EBV positive by in situ hybridization

Inflammatory Myofibroblastic Tumor	Interdigitating Dendritic Cell Sarcoma
ALK positive 35-60%	ALK negative
S100 negative	S100 positive