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Medical imaging in pediatric ophthalmology.pdf Medical imaging in pediatric ophthalmology Mahmood F. Mafee, MDa,*, Rana F. Mafee, MDb, Mahr Malik, MDc, Jill Pierce, MDc aDepartment of Radiology, University of Illinois at Chicago Medical Center, 1740 West Taylor Street, MC 931, Chicago, Illinois 60612, USA bEye and Ear Infirmary, University of Illinois at Chicago, Chicago, Illinois, USA cUniversity of Illinois at Chicago/Reese/Mercy Radiology Program, Mercy Hospital, 2525 South Michigan Avenue, Chicago, Illinois 60616, USA In the practice of ophthalmology, although many conditions can affect any age group, it is convenient to differentiate disorders that predominantly affect children from disorders that have greater predilection in adults. The evolution of advancing technologies has greatly influenced and aided in the differentiation of orbital and ocular lesions. Pediatric ophthalmologic diagnostic evaluation, in particular, has significantly improved with use of imaging modalities such as ultrasound, computed tomography (CT), and MR imaging. This article discusses the use of these modalities in the diagnosis of diseases most commonly seen in infants and children. General considerations In general CT scanning and MR imaging are the two modalities commonly used for imaging of the eye and the orbit. Each has advantages and disadvan- tages. Computed tomography is the modality of choice for showing bony detail and for detecting calcifications and foreign bodies. Irradiation to the ocular and orbital structures is a disadvantage, however. MR imaging, on the other hand, has no known biologic side effects and is superior to CT when evaluating soft tissue detail in the globe, orbit, visual pathways, and intracranial structures. MR imaging should not be used to evaluate the orbit or other parts of the body when there is suspicion of a ferromagnetic object in the body. A routine CT examination of the orbits includes axial and coronal sectioning with slices 5-mm thick. When there is suspicion for a small lesion, thinner sections of 3 or 1.5 mm should be obtained. Sections of 1.5- to 3-mm thickness are 0031-3955/03/$ – see front matter D 2003, Elsevier Science (USA). All rights reserved. doi:10.1016/S0031-3955(03)00002-6 * Corresponding author. E-mail address: mfmafee@uic.edu (M.F. Mafee). Pediatr Clin N Am 50 (2003) 259–286 essential for optimal demonstration of the optic nerve anatomy and pathology. Radiologists always tailor the examinations according to the clinical information and the preliminary diagnosis. For foreign bodies, it is important to obtain 1.5-mm axial sections. It is often unnecessary to obtain additional direct coronal sections for the localization of foreign bodies, because the use of computer reformatting is helpful in producing images in other planes. For foreign bodies or lesions at the 6 o’clock or 12 o’clock positions, it is always advisable to obtain direct coronal sections. For ocular pathology, thin sectioning (1.5 mm) is exceedingly important, because one can easily miss a lesion on routine 5-mm sections. For bony lesions or orbital fractures, in addition to the routine study, retrospective high-resolution, extended bone scale images should be obtained using a window width of about 4000 and a window level of 700 to 800. The use of intravenous iodinated con- trast material should be determined by clinical information and is best left to the discretion of the radiologist. In general contrast material is not used when evaluating for foreign bodies, uncomplicated orbital fractures, morphologic changes of extraocular muscles, developmental cysts (noninfected and non- ruptured dermoids, epidermoids, and dermolipomas), or bony lesions such as osteoma, osteoid osteoma, and fibrous dysplasia. Contrast-enhanced CT scanning is necessary for evaluation of patients suspected of having orbital infections, tumors such as rhabdomyosarcoma, osteochondrogenic sarcoma, leukemic infil- tration, and other primary or secondary lesions such as Langerhans’ cell histio- cytosis and metastatic neuroblastoma. Most orbital and ocular lesions can be evaluated by CT; however, MR imaging offers more information in the differentiation of various pathologic conditions that involve the eye and orbit. The success of MR imaging depends on cooperation of the patient and use of appropriate sedation as well as appropriate pulse sequences. The authors’ sedation and MR protocols have been described in detail elsewhere [1]. Although individual examinations should always be specifically tailored to the problems of each individual patient, there are general recommendations for orbital and ocular lesions. These include short time of repetition (TR) and short time of echo (TE), which provides a T1-weighted (T1W) pulse sequence, as well as a long TR and long TE, which provides a T2-weighted (T2W) pulse sequence. Precon- Fig. 1. Computed tomographic scan of orbital dermoid. Note calcification (arrows). (From Kaufman et al, Radiol Clin North Am 1998;36:1152, Fig. 4.) M.F. Mafee et al. / Pediatr Clin N Am 50 (2003) 259–286260 trast and postcontrast T1W images with and without fat suppression are obtained whenever intravenous contrast gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) is used. Pathology A variety of lesions warranting medical imaging involve the orbit and eye of pediatric patients. The list includes developmental anomalies, inflammation including idiopathic inflammatory conditions, tumors such as rhabdomyosarcoma and glioma, vascular anomalies, intraocular retinal pathology including retino- blastoma, papilledema, optic atrophy, the anophthalmic orbit, paralytic and restrictive strabismus, and trauma. Developmental orbital cysts A variety of cyst and cystlike lesions involve the orbit of pediatric patients. The most frequent developmental cysts involving the orbit and periorbital Fig. 2. T1-weighted MR image of conjunctival dermolipoma (arrows). (From Kaufman et al, Radiol Clin North Am 1998,36:1153, Fig. 9.) Fig. 3. Enhanced computed tomographic scan of orbital dermoid cyst (c). (From Kaufman et al, Radiol Clin North Am 1998,36:1152, Fig. 3.) M.F. Mafee et al. / Pediatr Clin N Am 50 (2003) 259–286 261 structures are choristomas, typically dermoid and epidermoid cysts, lipoder- moids, and teratomas. Choristoma is a focus of tissue histologically normal for an organ or part of an organ other than the site at which it is located [2–4]. Teratomas are choristomatous tumors that contain tissues representing two or more germ layers. The tumor can be either solid or cystic. The imaging modality of choice depends on the entity being considered. Computed tomographic scanning is indicated when a prominent feature of the suspected lesion is bone remodeling, bone destruction, bone or calcium depo- sition, or intralesional fat (Fig. 1). MR imaging may provide information about the characteristics of fluid and tissues within the cystic lesion (Fig. 2). Both epidermoid and dermoid cysts appear on CT scans as unenhanced, well-circum- scribed, smoothly marginated, low-density masses (Fig. 3). If a dermoid cyst contains fatty tissues, it has a fat density on CT scans (see Fig. 1). Calcification Fig. 4. (A) T1-weighted MR image of orbital dermoid showing a predominately hyper intense mass. (From Kaufman et al, Radiol Clin North Am 1998;36:1153., Fig. 7.) (B) Giant epidermoid in 14-year- old girl. Enhanced computed tomographic scan shows a large unenhanced mass with bone destruction, involving the superior aspect of left orbit. (C) Fast spin echo T2-weighted MR image of same patient as in Fig. 4 B, showing an extraconal hyperintense mass involving the superior aspect of left orbit. (Case courtesy of Dr. Hahn.) M.F. Mafee et al. / Pediatr Clin N Am 50 (2003) 259–286262 may be seen in dermoid cysts (see Fig. 1). Fat-fluid level may be present in dermoid cysts. On MR imaging, dermoid and epidermoid cysts have low signal intensity on T1W images and high signal intensity on T2W (Fig. 4), fluid- attenuated inversion recovery (FLAIR) pulse sequence, and diffusion-weighted MR images. A dermoid cyst that contains significant fatty tissue demonstrates typical MR imaging characteristics of fat–hyperintense on T1W images (Fig. 4A) and hypointense on T2W images. Both dermoid and epidermal cysts may demonstrate slight enhancement of their wall on postcontrast CT scans and MR images (see Fig. 3). Colobomatous cyst An ocular coloboma results from failure of the embryonic fissure to close. In a typical coloboma, the cleft appears in the inferonasal quadrant of the globe. In a small percentage of microphthalmic eyes with coloboma, a defect in the sclera allows an extraocular herniation of the intraocular neural ectoderm to form an orbital cyst. Computed tomographic and MR imaging may show a colobomatous defect in the globe, depending on the size of the coloboma. A cyst associated with a microphthalmic eye with coloboma can be easily identified on CT scans and MR imaging (Fig. 5A). Fig. 5. (A) Computed tomographic scan of colobomatous cyst showing microphthalmic eyes and bilateral colobomatous cysts (hollow arrows). Note dystrophic calcification at the colobomatous defect (white solid arrow). (B,C) MR images of another patient demonstrating optic nerve hypoplasia. Note microphthalmic eye and a perioptic nerve cyst in (C). M.F. Mafee et al. / Pediatr Clin N Am 50 (2003) 259–286 263 ...