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tochemical findings [3, 4]. Recent studies have revealed cytogenetic clonal abnormal-ity and anaplastic lymphoma kinase expres-sion, suggesting a neoplastic cause [5, 6]. However, inflammatory pseudotumor of the lymph node and spleen is a nonneoplas-tic entity distinct from inflammatory myofi-broblastic tumor. Furthermore, the family of idiopathic fibrosclerosing lesions, including sclerosing mesenteritis, idiopathic retroperi-toneal fibrosis, sclerosing mediastinitis, and orbital inflammatory pseudotumor, may also be considered within the umbrella of inflam-matory pseudotumor [7]. Thus inflammatory myoblastic tumor is not the same as inflam-matory pseudotumor.

Inflammatory pseudotumor most com-monly involves the lung and orbit, but it has been described in almost any location, in both sexes, at all ages [13]. Most cases oc-cur in childhood or early adulthood and may be asymptomatic or associated with consti-tutional complaints or symptoms, including unexplained fever and weight loss, and may be related to local mass effects [2, 4]. Inflam-matory pseudotumors clinically masquerade as malignant growths, and their clinical sig-nificance thus lies in the difficulty encoun-tered in preoperatively excluding malig-nancy. The preoperative recognition of this benign lesion is important to avoid unneces-sary radical resection. Although several cas-es of spontaneous regression and response to the medical treatment have been reported, in consideration of its pathologic features and clinical manifestations, complete surgical resection is mandatory, with the exception

Imaging Findings of Head and Neck Inflammatory Pseudotumor

Sung Bin Park1,2Jeong Hyun Lee2Young Cheol Weon3

Park SB, Lee JH, Weon YC

1Department of Radiology, Cheil General Hospital and Womens Healthcare Center, Kwandong University College of Medicine, Seoul, Korea.

2Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan, 388-1 Poongnap-dong, Songpa-gu, Seoul, 138-736, Korea. Address correspondence to J. H. Lee (jeonghlee@amc.seoul.kr).

3Department of Radiology, Ulsan University Hospital, University of Ulsan, Ulsan, Korea.

Neuroradiolog y / Head and Neck Imaging Pictor ia l Essay

CMEThis article is available for CME credit.See www.arrs.org for more information.

AJR 2009; 193:11801186

0361803X/09/19341180

American Roentgen Ray Society

Inflammatory pseudotumor is a rare benign condition of un-known cause. It is characterized by the presence of a mass that

may mimic malignancy and that is composed of spindle cells mixed with variable amounts of extracellular collagen, lymphocytes, and plasma cells [1, 2]. The imaging characteris-tics and locations of head and neck inflam-matory pseudotumor vary widely, with most-ly large masses mimicking malignant lesions. Although imaging features of inflammatory pseudotumor are nonspecific and not charac-teristic, the role of the radiologist is to ensure that inflammatory pseudotumors are preop-eratively suggested diagnoses and are differ-entiated from malignant lesions either by particular imaging findings or by imaging-guided biopsy.

In this article, we describe the imaging features of head and neck inflammatory pseudotumor in the brain, orbit, sinonasal cavity, temporal bone or skull base, and oth-er rare head and neck locations.

Pathogenesis and Clinical Manifestations of the Inflammatory Pseudotumor

Inflammatory pseudotumor is a chronic inflammatory tumefaction of unknown ori-gin. The cause and pathogenesis of inflam-matory pseudotumor remains controversial. Recently, the term inflammatory myofibro-blastic tumor has emerged from the broad category of inflammatory pseudotumor and has come to be commonly used on the ba-sis of electron microscopic and immunohis-

Keywords: CT, head and neck imaging, inflammatory myofibrotic tumor, inflammatory pseudotumor, MRI

DOI:10.2214/AJR. 09.2398

Received January 15, 2009; accepted after revision March 31, 2009.

OBJECTIVE. The purpose of this article is to describe imaging features of head and neck inflammatory pseudotumor in the brain, orbit, sinonasal cavity, temporal bone or skull base, and other rare locations.

CONCLUSION. Although the radiologic differentiation from malignancy is not clearly possible, we suggest that familiarity with the manifestations of inflammatory pseudotumor can help avoid unnecessary radical surgery before histopathologic proof of malignancy.

Park et al.Head and Neck Inflammatory Pseudotumor

Neuroradiology/Head and Neck ImagingPictorial Essay

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Head and Neck Inflammatory Pseudotumor

of steroid therapy for orbital inflammatory pseudotumor. The prognosis of inflamma-tory pseudotumor is generally considered to be favorable if complete surgical resection is done, with only a rare incidence of malignant transformation and remote metastasis [2].

Radiologic Features of the Inflammatory Pseudotumor

Although the radiologic findings of in-flammatory pseudotumor are nonspecific, particular findings are observed. Ultrasound shows a variable pattern of echogenicity with ill-defined or well-defined margins. Promi-nent vascularity may be shown with color or power Doppler ultrasound, especially con-trast-enhanced power Doppler ultrasound. Enhanced CT may show homo- or hetero-geneity and hypo-, iso-, or hyperdensity [8]. MRI shows a hypointense lesion on T1- and T2-weighted images (possibly explained by the relative lack of mobile protons within fi-brotic lesions) and shows marked gadolini-um enhancement. Delayed enhancement has frequently been observed, probably because of the accumulation of extravascular contrast media in fibrotic lesions [9].

Inflammatory Pseudotumor of the Brain

Inflammatory pseudotumor is extremely rare in the CNS without the involvement of other organ systems. These diseases may be located in the brain parenchyma (Fig. 1), at-tached to the dura (Fig. 2), or, rarely, may in-volve both [10].

Lack of neovascularization was shown by reduced cerebral blood volume on perfusion MRI (Fig. 1) and detection of lactate on MR spectroscopy, suggesting hypoxia and in-flammatory reaction. Loss of normal neural elements caused by proliferation of inflam-matory cells can be visualized by reduction of N-acetylaspartate on MR spectroscopy and loss of fractional anisotropy on diffu-sion tensor MRI. Increase of cellularity and cell membrane synthesis due to inflammato-ry cells hyperplasia has been visualized by an increase of choline in MR spectroscopy [10].

Inflammatory Pseudotumor of the Orbit

Orbital pseudotumors are the third most common primary tumor of the orbit. The in-cidence has been reported to be 9% of all orbital mass lesions and these tumors are a common cause of unilateral proptosis in adults [1, 11]. Orbital pseudotumor is diag-nosed by exclusion, on the basis of the pa-

tients history, clinical course, response to steroid therapy, laboratory tests and, biopsy findings. The symptoms of orbital pseudo-tumors reflect the degree of the inflamma-tory response (acute, subacute, or chronic) and the location of the inflammatory tissue [11, 12].

They usually show an abnormal intraor-bital soft-tissue mass density that varies con-siderably in size, shape, and location. On CT, a moderately enhancing mass is usually seen (Fig. 3). Orbital pseudotumors are commonly accompanied by fat infiltration or edema. A bony change reflected by hyperostosis and re-modeling favors the diagnosis of a longstand-ing benign process, such as an orbital pseudotu-mor that is sometimes found to extend through the superior orbital fissure and to enlarge and erode the fissure compared with the normal side. MRI shows a hypointense lesion on T1- and T2-weighted images and shows marked gadolinium enhancement. Fat-suppression tech-niques clearly show an optic nerve sheath lesion and intraorbital inflammation.

The spectrum of orbital involvement var-ies from localized periscleritis or perineuri-tis to diffuse orbital inflammation frequently involving the lacrimal gland and the mus-cular cone. When the muscular cone is in-volved, imaging studies, including CT and MRI, characteristically reveal thickening of the extraocular muscle belly and relative sparing of the tendon [11, 13]. However, ex-tension beyond the orbit can occur in cases of extensive and chronic orbital inflamma-tion [11] (Fig. 4). The middle cranial fossa and cavernous sinus are the two most com-mon locations into which extensions are ob-served. Direct intracranial spread can occur through the superior orbital fissure, the infe-rior orbital fissure, or the optic canal [12].

Inflammatory Pseudotumor of the Sinonasal Cavity

Sinonasal inflammatory pseudotumors have a more aggressive appearance than those of the orbit, with bony changes such as ero-sion, remodeling, and sclerosis being common [14] (Figs. 5 and 6). Characteristics include less response to corticosteroid treatment than orbital pseudotumors; if the tumor is com-pletely resected, the prognosis is good.

Inflammatory Pseudotumor of the Temporal Bone or Skull Base

Inflammatory pseudotumors rarely occur in the temporal bone or skull base. It is very difficult, both clinically and radiologically, to determine whether an infiltrating soft-tissue

mass located in the temporal bone or skull base, with bone destruction, is an inflamma-tory pseudotumor or a malignant neoplasm [15, 16].

Common MRI findings in all reported cas-es are low signal intensity on T2-weighted images and homogeneous contrast enhance-ment (Figs. 7 and 8). Dural thickening and enhancement are nonspecific reactive chang-es to any adjacent dural lesion and can also manifest with malignant neoplasm (Figs. 7 and 8). The pattern of a soft-tissue mass characterized by low signal intensity on T2-weighted images, marked contrast enhance-ment, a peculiar destruction of the mastoid, and sparing of the inner ear and of the ossic-ular chain is contraindicative of an aggres-sive tumor and likely suggests a chronic in-flammatory lesion [15].

Other Rare Locations of Head and Neck Inflammatory Pseudotumor

Other rare locations include inflamma-tory pseudotumor in the soft tissue of the neck (Fig. 9), the infratemporal fossa, the nasopharynx including the parapharyngeal space, the pterygopalatine fossa, the larynx, and the major salivary gland.

ConclusionThe imaging characteristics and locations

of head and neck inflammatory pseudotu-mor vary widely, from the more frequent be-nign lesions such as large masses mimicking malignant lesions to the rare tumors that are multifocal and prone to recurrence and ma-lignant transformation (Fig. 6). Inflammato-ry pseudotumor can also manifest as brain abscess (Fig. 1) and meningioma (Fig. 2). The role of the radiologist is to ensure that inflammatory pseudotumors are preopera-tively suggested diagnoses and differentiated from malignant lesions either by particular imaging findings or by imaging-guided biop-sy. Thus, although the radiologic differentia-tion from malignancy is not clearly possible, we suggest that familiarity with the mani-festations of inflammatory pseudotumor can help avoid unnecessary radical surgery be-fore histopathologic proof of malignancy.

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orbital inflammatory pseudotumors with extraor-bital extension. Korean J Radiol 2005; 6:8288

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A

Fig. 163-year-old man with inflammatory pseudotumor of brain. Inflammatory pseudotumor manifests parenchymal involvement and mimics abscess.A and B, T2-weighted (A) and FLAIR (B) MR images show high-signal-intensity lesion with peripheral dark signal intensity rim in right parietal area. Perilesional high signal intensity, presumed edema, is also evident.C, Contrast-enhanced T1-weighted MR image shows peripheral rim enhancement.D, Diffusion-weighted MR image shows high-signal-intensity lesion in right parietal area. High signal intensity due to perilesional edema on T2-weighted MR image changes to dark signal intensity.E, Perfusion-weighted MR image shows blue lesion in right parietal area, suggestive of decreased perfusion compared with surrounding red colored coding normal brain parenchyma.

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Fig. 267-year-old man with inflammatory pseudotumor of brain. Inflammatory pseudotumor is attached to dura and manifests as meningioma.A, T1-weighted MR image shows dural-based iso- to slightly low-signal-intensity lesion in left parietal area. B, T2-weighted MR image shows dark signal intensity lesion that was falsely identified as calcified mass.C and D, Contrast-enhanced T1-weighted MR images show strong homogeneous enhancement of mass and surrounding dura (arrow, D). Radiologic diagnosis was calcified meningioma. Surgically excised specimen indicated lymphoplasma cellrich inflammatory pseudotumor.

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Fig. 353-year-old woman with inflammatory pseudotumor of orbit who presented with left-sided diplopia and proptosis.A and B, Axial CT scans of orbit show homogeneously enhancing soft-tissue mass (M) in left lacrimal gland. Mass is attached to left lateral and superior rectus muscle. Bony changes such as erosion and sclerotic change (arrow) are also evident. Patient was treated with high dose of corticosteroids, and symptoms resolved.

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Fig. 438-year-old woman with orbital inflammatory pseudotumor and extraorbital extension.A, Axial CT scan of orbit shows suspicious soft-tissue density in right cavernous sinus (arrow).B, T1- and T2- weighted axial MR images showed iso- and low-signal-intensity lesion (not shown). Contrast-enhanced T1-weighted MR image shows plaquelike enhancing lesion (arrow) in right temporal pole to cavernous sinus. Tolosa-Hunt syndrome is suggested.

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Fig. 547-year-old woman with inflammatory pseudotumor of nasal cavity.A and B, Axial (A) and coronal (B) CT scans show soft-tissue lesion in nasal cavity. Mild nasal septal deviation to left side is also evident.C, Photomicrograph of histologic specimen shows loosely arranged spindle cells, admixed collagen bundles, and scattered inflammatory infiltrate. Mitotic activity was low, and cellular atypia was minimal. (H and E, original magnification 40)D, On higher power, photomicrograph of histologic specimen shows cytologically bland spindle cells with prominent admixture of lymphocytes and plasma cells. (H and E, original magnification 400)E, Photomicrograph of immunohistochemistry shows strong positive finding of myofibroblasts for smooth muscle actin. (Original magnification 400)

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Fig. 671-year-old man with inflammatory pseudotumor and malignant transformation of left maxillary sinus. Patient had left gingival pain for 6 months.A and B, Axial (A) and coronal (B) CT scans show soft-tissue lesion (M in B) in left maxillary sinus. Associated massive bony destructions are evident. Radiologic primary diagnosis was malignant lesion with bony destruction. Wide excision was performed. Pathologic results indicated inflammatory pseudotumor with malignant transformation.

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Fig. 745-year-old woman with inflammatory pseudotumor of temporal bone.A and B, T1- (A) and T2- (B) weighted MR images show intermediate signal intensity lesion in right mastoid and petrous portion of right temporal bone.C and D, Contrast-enhanced T1-weighted MR images show strong homogeneous enhancement of mass and surrounding dura (arrows, D). Extension to cavernous sinus is also evident.

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Fig. 869-year-old woman with inflammatory pseudotumor of skull base.A and B, T1- (A) and T2- (B) weighted MR images show iso- and slightly high-signal-intensity lesion in right middle cranial fossa and skull base.C and D, Contrast-enhanced T1-weighted MR images show strong homogeneous enhancement of bony destructive mass and surrounding dura. Extension to cavernous sinus engulfing right carotid artery (arrow, D), ethmoid sinus, temporal bone, and clivus is also evident.

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Fig. 917-year-old girl with inflammatory pseudotumor of soft tissue of neck.A and B, Axial (A) and coronal (B) CT scans of neck show ill-defined homogeneously enhancing soft-tissue mass (M) in left posterior cervical area and extension to carotid space and subcutaneous layer. Associated lymphadenopathies (arrows, B) are also evident.

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F O R Y O U R I N F O R M A T I O N

This article is available for CME credit. See www.arrs.org for more information.

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