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Neuroradiology Case of the Week

Case 291

Justin Brucker, CC4

Clinical Presentation: Patient is a 47-year-old female who presents with headaches and visual changes. CT of the head was obtained to evaluate for intracranial mass.

Imaging Findings: Head CT: The frontal sinuses demonstrate ground-glass haziness, bone thickening, and enlargement, particularly along the right orbital roof (Fig. 1). The ethmoid, sphenoid, and mastoid sinuses are clear (Fig. 2). There are no intracranial abnormalities or mass effect.

Diagnosis: Fibrous dysplasia of the frontal sinuses

Discussion: Fibrous dysplasia (aka. Lichtenstein-Jaffe disease) is a congenital skeletal disorder that is characterized by one or more benign intramedullary fibro-osseous lesions. It accounts for 1% of primary bone tumors [6], 5-7% of benign bone tumors [3], and is the most common of these within the craniofacial region [6]. Monostotic (single bone) fibrous dysplasia is 4-6 times more common than the polyostotic form [1, 6]. Craniofacial involvement occurs in 10-25% of the former cases and 50% of the latter, typically within the frontal, ethmoidal, sphenoid, and maxillary sinuses [1]. Men and women are equally affected, and usually become symptomatic between 10-30 years of age.
     Patients with fibrous dysplasia may present with bone pain, deformity, or possibly fracture. Craniofacial involvement can present as a wide range of symptoms: facial swelling/distortion (leontiasis ossea), pain, orbital displacement, cranial nerve palsies, vision and hearing loss, etc… or it may simply be an incidental finding. Only 0.5% of these lesions undergo malignant transformation [4]. Polyostotic disease may coexist with McCune-Albright disease (skin-pigmentation, precocious puberty, and endocrine disorders) or Mazabraud syndrome (multiple intramuscular myxomas). Association with hepatobiliary disease, cardiac disease, or endocrinopathies (hyperprolactinemia, hyperthyroidism, hyperpituitarism, hyperparathyroidism, Cushing's syndrome, diabetes mellitus) may also occur [5, 6].
     Plain films and CT are useful for diagnosing fibrous dysplasia, which visualizes as an ill-defined, expansile mass with a ground-glass appearance. The lesion may also feature cystic, sclerotic, and/or Pagetoid components [2]. CT is particularly useful for determining the extent of craniofacial lesions and assessing for foraminal compromise [2, 7]. MR yields a more heterogeneous picture, with some aspects of the mass intensifying variably on T2 or hypointensifying on T1 [5]. However, these images will not demonstrate bone and air as well as CT, and may instead falsely suggest a threatening malignancy [2]. CT may also be needed to differentiate the lesion from an ossifying fibroma, which demonstrates a stellate nidus of calcification on film, but is histogically indistinguishable from fibrous dysplasia [2].
     The ground-glass appearance seen radiographically is due to the replacement of normal medullary bone with a fibrous, collagenous stroma intermixed with sparse bone spiculae. These dysplastic trabeculae are the work of dysfunctional osteoblasts, few in number, that behave like immature, undifferentiated pre-osteogenic cells [6]. In the case of McCune-Albright Syndrome, the putative gene is on chromosome 20q13.2-13.3, and encodes for the Gs-alpha subunit. Mutations of this subunit lead to disregulation of cAMP and IL-6 expression; a pathway most likely involved in other forms of fibrous dysplasia.
     Disease progression can be slowed through the use of bisphosphonates, but surgical management may be warranted in many cases.

References:

1. Anand MKN. Fibrous dysplasia. EMedicine. April 5, 2007. http://www.emedicine.com/radio/topic284.htm
2. Branstetter BF 4th, Weissman JL. Role of MR and CT in the paranasal sinuses. Otolaryngol Clin North Am. 2005 Dec;38(6):1279-99. [Medline]
3. DiCaprio M, Enneking W.Fibrous dysplasia. Pathophysiology, evaluation, and treatment. J Bone Joint Surg Am. 2005 Aug;87(8):1848-64. [Medline]
4. Hunt JA, Hobar PC. Common craniofacial anomalies: conditions of craniofacial atrophy/hypoplasia and neoplasia. Plast Reconstr Surg. 2003 Apr 1;111(4):1497-508; quiz 1509-10. [Medline]
5. Kransdorf MJ, Moser RP Jr, Gilkey FW. Fibrous dysplasia. Radiographics. 1990 May;10(3):519-37. [Medline]
6. Singer FR. Fibrous dysplasia of bone: the bone lesion unmasked. Am J Pathol. 1997 Dec;151(6):1511-5. [Medline]
7. Stevens J, Murray A, Saunders D, Lane B. Cranial and Intracranial Pathology. IN: Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging, 4th ed. Churchill Livingstone, Inc. 2001.