tumor

Inflammatory Myofibroblastic Tumor of the Skull

Mariam Fahim, DO
Judith Oh Leonor, OMS-IV
Volume 15 - Issue 2 - February 2016

(A) MRI of the brain, sagittal view, T1-weighted image; and (B) sagittal view, T2-weighted image. A term-appropriate for gestational age male born via normal spontaneous vaginal delivery with unremarkable prenatal labs was noted to have a 1-cm lesion near the vertex of the skull. The lesion was thought to be a cephalohematoma and he was discharged home.

At 6 months old, the infant was developing normally without any localizing neurological symptoms. On physical examination, he had a soft, nontender mass in the parietal-occipital region measuring about 2.0 × 2.5 cm with well-defined borders. Ultrasound of the head showed an echogenic well-defined mass with high vascularity that appeared to be extra-axial, causing mass effect on the brain. Follow-up magnetic resonance imaging (MRI) of the head showed large intensely enhancing 2.7 × 3.5 × 2.5-cm extra-axial heterogeneous mass centered along the right paramedian posterior parietal bone (Figure).

He had a craniotomy for resection of supratentorial tumor and biopsy of the mass. The tumor was in between dural leaflets with adherence to adjacent draining veins and the superior sagittal sinus. 

Hematology described the tissue as a mixture of bland spindle cells and scattered large cells in a background of inflammatory cells, including plasma cells, lymphocytes, and eosinophils. Immunohistochemistry showed stellate fibroblastic cells diffusely positive of anaplastic lymphoma kinase (ALK)-1, diagnostic of inflammatory myofibroblastic tumor (IMT) of the skull. The infant was to be followed closely with serial imaging with the next MRI of the head in 3 months.  

IMT is classified as a low-grade benign tumor composed of myofibroblasts with inflammatory infiltrate.1 IMT occurs most commonly in the pulmonary parenchyma, but may occur in extrapulmonary sites.2 

Contrast-enhanced computed tomography and MRI may show a homogeneous or heterogeneous enhancement of the lesion, as well as calcification within the tumor (seen more commonly in children than in adults).3 On MRI, IMT is hypointense to isointense relative to muscle on T1-weighted images, and has a relatively hypointense T2 signal compared to other lesions.3 Diagnosis of IMT is difficult without biopsy of the lesion. 

IMT has similar histologic features to IgG4-related inflammatory pseudotumor (IPT), but IPT is managed conservatively with corticosteroids and IMT by surgical excision with adjuvant corticosteroid therapy.4 Radiotherapy has been shown to be ineffective in IMT.2 Histologically, bland-looking spindle cells with fibrosis and an inflammatory infiltrate containing plasma cells and lymphocytes are found in both IMT and IPT. However, spindle cell proliferation is more prominent in IMT with low level of IgG4+ cell infiltration than in IPT. Expression of ALK that codes for a receptor tyrosine kinase is seen in IMT, but not in IPT.5 About 50% of IMTs are positive for ALK, which is more common in younger patients. Less than 5% of cases may act more aggressively and metastasize.5 Although IMT have low mitotic rates, complete surgical excision of IMT is indicated.5 Possible future treatments include ALK inhibitors such as crizotinib for ALK positive IMT and cyclo-oxygenase 2 inhibitors for ALK negative IMT; however, these therapies require further studies.2n

References

  1. Coffin CM, Watterson J, Priest JR, Dehner LP. Extrapulmonary inflammatory myofibroblastic tumor (inflammatory pseudotumor). A clinicopathologic and immunohistochemical study of 84 cases. Am J Surg Pathol. 1995;19(8):859-72.
  2. Jindal A, Bal A, Agarwal R. Inflammatory myofibroblastic tumor of the trachea in the pediatric age group: case report and systematic review of the literature. J Bronchology Interv Pulmonol. 2015;22(1):58-65.
  3. Oguz B, Ozcan HN, Omay B, Ozgen B, Haliloglu M. Imaging of childhood inflammatory myofibroblastic tumor. Pediatr Radiol. 2015;45(11):1672-1681.
  4. Maire JP, Eimer S, San Galli F, et al. Inflammatory myofibroblastic tumour of the skull base. Case Rep Otolaryngol. 2013;2013:103646.
  5. Bhagat P, Bal A, Das A, Singh N, Singh H. Pulmonary inflammatory myofibroblastic tumor and IgG4-related inflammatory pseudotumor: a diagnostic dilemma. Virchows Arch. 2013;463(6):743-747.