Ann Otol Rhinal LaryngollOl:1992
IMAGING CASE STUDY OF THE MONTH
FIBROUS DYSPLASIA OF THE SPHENOID SINUS DONALD P. MUELLER, MD KENNETH D. DOLAN, MD
WILLIAM
T. C. YUH, MD
IOWA CITY , IOWA
CASE REPORT
Radiographically the pattern was consistent with fibrous dysplasia. Neurologic and neurosurgical consultations were obtained. The consensus was that the patient was asymptomatic with respect to the osseous change. No further therapy or diagnostic procedure was deemed warranted.
A 31-year-old man with a history of recent onset of seizures, controlled by Tegretol, was evaluated by cerebral magnetic resonance imaging (MRI). Axial images were obtained. The dominant finding was in the left sphenoid sinus and greater wing. Proton density (TR 2,400/TE 20) images demonstrated low signal in the left sphenoid sinus with extension into the adjacent left middle cranial fossa. Some inhomogeneity was seen. The dominant pattern was decreased signal compared to that of bone marrow. With increased T2 weighting (TR 2,400/ TE 70) the signal remained low compared to that of adjacent brain. No meningeal enhancement was identified following gadolinium administration (Fig 1).
DISCUSSION
Magnetic resonance imaging is based on hydrogen atom resonance. The primary source of signal is fat or water. Both the quantity of atoms and their local environment affect the signal. In general, inflammatory sinus lesions demonstrate increased signal on T2-weighted images. A low T2 signal indicates decreased water content. Within the sinuses, a loss of T2 signal indicates either an aggressive lesion such as a neoplasm or dried secretions. 1
Enhanced computed tomography was then performed. Predominately sclerotic change with thickening of bone in the left sphenoid sinus and adjacent proximal pterygoid and greater sphenoid wing was seen. This corresponded to the MRI signal abnormality (Fig 2).
Fibrous dysplasia is a disorder of unknown origin in which normal bone is replaced by fibrous tissue
B Fig 2. Computed tomograms of skull base. A) Axial, showing sclerosis and expansion of left sphenoid greater wing. B) Coronal, showing sclerosis of left sphenoid sinus and sclerosis and expansion of proximal pterygoid and greater wing.
Fig 1. Magnetic resonance images of skull base. A) Axial T2-weighted, showing signal loss and expansion of left sphenoid greater wing. B) Coronal, contrast-enhanced TIweighted, showing abnormal signal in left sphenoid sinus.
From the Department of Radiology, The University of Iowa College of Medicine, Iowa City, Iowa. REpRINTS - Donald P. Mueller, MD, Dept of Radiology, The University of Iowa Hospitals and Clinics, Iowa City, IA 52242.
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Mueller et al, Imaging Case Study of the Month
and poorly formed woven bone." Leeds and Seamarr' identified the frontal and sphenoid bones as the most common sites of calvaria involvement. Symptoms relate to bony overgrowth. Proptosis, foraminal compression, and deafness all may occur." Three plain film radiographic patterns have been described. Homogeneous density is seen in the sclerotic pattern. Relative lucency that frequently has dense margins is identified in the cystlike pattern. The pagetoid form is a mixed lesion with alternate areas of relative density and lucency. Varying proportions of radiolucent fibrous tissue and radiodense bone account for the spectrum of plain film patterns. 4 A spectrum of MRI signal characteristics has also
101
been reported. The signal on Tl-weighted images is consistently decreased, with an intensity similar to that of skeletal muscle. The T2 signal, however, is variable. The signal may be brighter than, similar to, or less than that of subcutaneous fat." It is assumed that the signal changes relate to the varying histology of the lesion. In summary, our case demonstrated T2 signal loss within the sphenoid sinus with extension into the adjacent middle cranial fossa. Computed tomography confirmed that predominately sclerotic bony thickening was the source of the decreased signal. Enhanced MRI failed to demonstrate an adjacent meningioma as a source for hyperostosis. The lesion was therefore considered to be radiographically characteristic of fibrous dysplasia.
REFERENCES 1. Shapiro MD, Som PM. MRI of the paranasal sinuses and nasal cavity. Radiol Clin North Am 1989;27:447-75.
its differential diagnosis. Radiology 1962;78:570-82.
2. Feldman MD, Rao VM, Lowry LD, Kelly M. Fibrous dysplasia of the paranasal sinuses. Otolaryngol Head Neck Surg 1986;95:222-5.
4. Fries JW. The roentgen features of fibrous dysplasia of the skull and facial bones. AJR 1957;77:71-88.
3. Leeds N, Seaman WB. Fibrous dysplasia of the skull and
5. Utz JA, Kransdorf MJ. MR appearance of fibrous dysplasia. J Comput Assist Tomogr 1989;13:845-51.
IMAGING CASE STUDY OF THE MONTH
FIBROUS DYSPLASIA OF THE SPHENOID SINUS DONALD P. MUELLER, MD KENNETH D. DOLAN, MD
WILLIAM
T. C. YUH, MD
IOWA CITY , IOWA
CASE REPORT
Radiographically the pattern was consistent with fibrous dysplasia. Neurologic and neurosurgical consultations were obtained. The consensus was that the patient was asymptomatic with respect to the osseous change. No further therapy or diagnostic procedure was deemed warranted.
A 31-year-old man with a history of recent onset of seizures, controlled by Tegretol, was evaluated by cerebral magnetic resonance imaging (MRI). Axial images were obtained. The dominant finding was in the left sphenoid sinus and greater wing. Proton density (TR 2,400/TE 20) images demonstrated low signal in the left sphenoid sinus with extension into the adjacent left middle cranial fossa. Some inhomogeneity was seen. The dominant pattern was decreased signal compared to that of bone marrow. With increased T2 weighting (TR 2,400/ TE 70) the signal remained low compared to that of adjacent brain. No meningeal enhancement was identified following gadolinium administration (Fig 1).
DISCUSSION
Magnetic resonance imaging is based on hydrogen atom resonance. The primary source of signal is fat or water. Both the quantity of atoms and their local environment affect the signal. In general, inflammatory sinus lesions demonstrate increased signal on T2-weighted images. A low T2 signal indicates decreased water content. Within the sinuses, a loss of T2 signal indicates either an aggressive lesion such as a neoplasm or dried secretions. 1
Enhanced computed tomography was then performed. Predominately sclerotic change with thickening of bone in the left sphenoid sinus and adjacent proximal pterygoid and greater sphenoid wing was seen. This corresponded to the MRI signal abnormality (Fig 2).
Fibrous dysplasia is a disorder of unknown origin in which normal bone is replaced by fibrous tissue
B Fig 2. Computed tomograms of skull base. A) Axial, showing sclerosis and expansion of left sphenoid greater wing. B) Coronal, showing sclerosis of left sphenoid sinus and sclerosis and expansion of proximal pterygoid and greater wing.
Fig 1. Magnetic resonance images of skull base. A) Axial T2-weighted, showing signal loss and expansion of left sphenoid greater wing. B) Coronal, contrast-enhanced TIweighted, showing abnormal signal in left sphenoid sinus.
From the Department of Radiology, The University of Iowa College of Medicine, Iowa City, Iowa. REpRINTS - Donald P. Mueller, MD, Dept of Radiology, The University of Iowa Hospitals and Clinics, Iowa City, IA 52242.
100
Mueller et al, Imaging Case Study of the Month
and poorly formed woven bone." Leeds and Seamarr' identified the frontal and sphenoid bones as the most common sites of calvaria involvement. Symptoms relate to bony overgrowth. Proptosis, foraminal compression, and deafness all may occur." Three plain film radiographic patterns have been described. Homogeneous density is seen in the sclerotic pattern. Relative lucency that frequently has dense margins is identified in the cystlike pattern. The pagetoid form is a mixed lesion with alternate areas of relative density and lucency. Varying proportions of radiolucent fibrous tissue and radiodense bone account for the spectrum of plain film patterns. 4 A spectrum of MRI signal characteristics has also
101
been reported. The signal on Tl-weighted images is consistently decreased, with an intensity similar to that of skeletal muscle. The T2 signal, however, is variable. The signal may be brighter than, similar to, or less than that of subcutaneous fat." It is assumed that the signal changes relate to the varying histology of the lesion. In summary, our case demonstrated T2 signal loss within the sphenoid sinus with extension into the adjacent middle cranial fossa. Computed tomography confirmed that predominately sclerotic bony thickening was the source of the decreased signal. Enhanced MRI failed to demonstrate an adjacent meningioma as a source for hyperostosis. The lesion was therefore considered to be radiographically characteristic of fibrous dysplasia.
REFERENCES 1. Shapiro MD, Som PM. MRI of the paranasal sinuses and nasal cavity. Radiol Clin North Am 1989;27:447-75.
its differential diagnosis. Radiology 1962;78:570-82.
2. Feldman MD, Rao VM, Lowry LD, Kelly M. Fibrous dysplasia of the paranasal sinuses. Otolaryngol Head Neck Surg 1986;95:222-5.
4. Fries JW. The roentgen features of fibrous dysplasia of the skull and facial bones. AJR 1957;77:71-88.
3. Leeds N, Seaman WB. Fibrous dysplasia of the skull and
5. Utz JA, Kransdorf MJ. MR appearance of fibrous dysplasia. J Comput Assist Tomogr 1989;13:845-51.
