mercoledì 20 dicembre 2000
CT: Expansion of the sphenoid sinus by a soft-issue density. The clivus appears eroded.
MRI: Expanded sphenoid sinus. Homogeneous material is present within the sinus cavity which is both T1 bright and T2 bright. Mass effect is present on both cavernous sinuses. The sellar contents appear normal. There is no evidence of enhancement with gadolinium.
Diagnosis: Sphenoid sinus mucocele
Mucocele is the most common lesion to cause expansion of the paranasal sinuses and results from the accumulation of mucoid secretions within an obstructed sinus or an obstructed chamber within a septated sinus. Both mucoceles and mucous retention cysts are formed by cuboidal epithelium surrounding mucoid secretions. Mucoceles fill a sinus cavity when the draining sinus ostia are blocked, usually by inflammatory changes or a tumor.
Mucoceles are more common in adults and usually a history of prior sinusitis or sinus polyposis can be obtained. Mucoceles are more common in individuals with cystic fibrosis. Classic mucoceles are non-infected and present with complaints resulting from the mass effects such as proptosis, frontal bossing, inability to breathe through the nose, orbital mass (frontal or ethmoidal), medial gaze abnormality (ethmoid), or a change in voice pitch. Pain is unusual and implies super infection. The most commonly involved sinuses are the frontal (60%) > ethmoid (30%) > maxillary (10%) > sphenoid (1%). Sphenoid sinus mucoceles have the highest rate of surgical complications (blindness) reflecting their proximity to the optic nerves. Sphenoid mucoceles usually expand antero-laterally into the ethmoid sinuses and orbital apices. Expansion may also occur into the sella, the cavernous sinuses, into the nasopharynx, or intra-cranially (rarely).
Sinus expansion can occur with mucoceles or neoplasms. The CT appearance of a soft tissue mass can be similar to mucocele. Sinusitis does not expand the sinus cavity. Surrounding bony sclerosis suggests infection. Calcifications may be present with superimposed fungal infections.
Surgical drainage (transsphenoidal marsupialization into an adjacent sinus cavity).
Plain film: The sinus may appear clouded, and the normal scalloped contour is lost as the mass enlarges. The normal white mucoperiosteal line is poorly seen. If preceded by chronic sinusitis, the sinus bones may show reactive bony changes.
CT: Mucocele usually appears as an expanded sinus cavity filled with material of homogeneous mucoid attenuation (10-0 HU). Rarely the material is of higher attenuation thought due to a higher protein content. Mucoceles generally do not enhance.
MRI: Signal is dominated initially by water content (95%). With chronicity (several months) the protein concentration and viscosity of the fluid increase and so does the T1WI signal. Usually T2WI bright; may decrease with time and lower water content.
martedì 12 dicembre 2000
CT(I-) axial and coronal images show bilateral proptosis, left greater than right, and bilateral extraconal soft tissue density masses in both the anterior and posterior portions of the orbit. The masses are contiguous with the lacrimal glands. No gross evidence of bony destruction.
Diagnosis: Orbital lymphoma
The extra nodal presentation of non-Hodgkin's lymphoma is common. Lymphoid masses account for approximately 10 to 15% of all orbital masses. Lymphoid neoplasms of the orbit include a wide range of classifications ranging from reactive lymphoid hyperplasias to benign pseudotumors to malignant lymphomas. Approximately 75% of patients with orbital lymphoma have or will have systemic lymphoma. The most common cytologic forms of malignant lymphoma involving the orbit are the histiocytic and lymphocytic types. Whether malignant lymphomas actually originate in the orbit and disseminate to the rest of the body or whether they represent metastatic sites remains unknown.
Lymphoid neoplasms of the orbit most commonly present in the sixth or seventh decades. True lymphoid tissue in the orbit is found in both the lacrimal glands and the subconjunctival tissue. Most of the lymphoid neoplasms occur at these two sites. Lymphomas tend to occur in the anterior portions of the orbit, most commonly involving the lacrimal glands, the eyelids and the subconjunctiva. In patients with lymphoma, the development of symptoms tends to be indolent and progressive. Symptomatology depends on whether the disease involves the anterior or retrobulbar portion of the orbit. With retrobulbar disease, patients may present with proptosis, eyelid swelling and pain.
In contrast, patients with pseudo-lymphoma (pseudotumor) present at a younger age with symptoms that develop suddenly and progress rapidly. Extensive signs of inflammation, eyelid erythema, pain, visual loss and motility disturbance may be present. Orbital cellulitis is an important consideration in the differential diagnosis.
CT shows homogeneous, sharply marginated, mildly enhancing mass or masses of soft-tissue density which frequently mold to preexisting structures. No bony erosion or enlargement of the orbit.
mercoledì 6 dicembre 2000
Findings: MRI (axial T1 pre- and post -gadolinium, axial T2): There is increased T1 signal and decreased T2 signal with in the region of the medial ciliary body of the left orbit, which demonstrates enhancement after the administration of gadolinium.
Diagnosis: Melanoma of the ciliary body
The uvea (choroid, iris, and ciliary body) is derived from neuroectoderm and mesoderm and may develop tumors from both origins. Malignant melanoma is the most common primary intraocular tumor of adulthood. It arises from the choroid in 75% of the cases but the iris, the ciliary body and the optic nerve head are other sites of reported involvement. Those involving the ciliary body and choroid are thought to originate from preexisting nevi. Metastatic sites of primary uveal melanoma include the liver, lungs, bones and kidney in order of decreasing frequency. The demonstration of the tumor in relation to the sclera is important as the prognosis is worse in-patients with tumor extension beyond the sclera.
The most common malignancy found in the orbit is a metastatic deposit. The richly vascularized choroid layer is the most common site of involvement. Malignant cells gain access to the globe by way of the bloodstream via the posterior ciliary arteries explaining why most deposits are in the posterior portion of the eye. Breast, lung and kidney carcinomas have the highest incidence of ocular involvement.
Small choroidal melanomas (less than 10mm in diameter and 3mm in thickness) have a generally favorable prognosis with a 85-90% survival rate at 5 years. Clinically stable choroidal melanomas (no visible increase in size) are managed by serial observations by clinical exam, and CT or MR imaging. Distant metastatic disease and extraocular extension, however, has occurred in visibly stable lesions. With evidence of tumor growth, enucleation and wide local excision is performed.
Uveal melanomas can be detected by ophthalmologic exam, fluorescein angiography ,or sonography. Both MR and CT are accurate in determining the size and location of uveal melanomas but MR is superior in assessing for the presence of retinal detachment or vitreous change and for differentiating uveal melanoma from choroidal hemangioma or choroidal detachment.
Uveal melanoma usually appears as a well defined, solid mass but when hemorrhagic or necrotic foci are present, the heterogeneity can cause diagnostic problems. Organized subretinal hemorrhage may have MR characteristics similar to uveal melanoma.
MR: Uveal melanomas are unique among the malignant tumors in that both T1 and T2 are shortened secondary to the paramagnetic properties of melanin. Melanin produces a stable free radical signal under all known conditions which enhances proton relaxation. The degree of shortening corresponds to the melanin content. The lesion is hyperintense on T1 weighted images and hypointense on T2 weighted images. MR imaging can not differentiate amelanotic melanoma from other tumors.
CT: Elevated, sharply marginated, hyperdense lesions demonstrating mild to moderate enhancement following contrast administration