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9 Ocular Ultrasound Dasia Esener INDICATIONS • Assess vision loss or impairment • Evaluate eye trauma IMAGE ACQUISITION AND INTERPRETATION Equipment • High frequency linear probe • High frequency endocavity probe Preparation • Sterile adhesive for eye protection • Ultrasound gel Steps 1. Identify normal structures. 2. Identify abnormal structures and foreign bodies. Sonographic Landmarks 1. 2. 3. 4. 5. 6. 7. 8. 9. Cornea Anterior chamber Pupil Ciliary body Posterior chamber Lens artifact Vitreous Retina Optic nerve 59 60 Clinical Ultrasound: A How-To Guide Step 1: Identify normal structures • Place probe in transverse orientation over the center of the eye with probe indicator pointing temporally.1 • Rest the wrist or little finger on the patient’s face to avoid unnecessary pressure on eye. • Identify the lens, vitreous, and retina. • Note that the retina is hyperechoic and tethered at the optic nerve; the vitreous is anechoic. • Have patient move eye left, right, up, and down. • Change probe positioning to the sagittal orientation and repeat the exam. • Evaluate both the affected and non-affected eye. Step 2: Identify abnormal structures and foreign bodies • Have the patient look in all four directions while observing movement within the globe such as vitreous hemorrhage, foreign bodies, or detached retina. • Foreign body (*). 1 The macula is temporal to the optic nerve; placing the probe indicator temporally ensures that the macula is always on the side of the indicator on the screen. This is important when evaluating retinal pathology. Ocular Ultrasound • Ocular lymphoma (*). • Retinal detachment (*). • Note when the retina detaches, a thin, hyperechoic membrane floats freely in the vitreous (*). 61 62 Clinical Ultrasound: A How-To Guide • Evaluate whether the detached retina extends beyond the macula. • Note that retinal detachments that extend past the retina are considered “macula off” and will have central vision abnormalities on eye exam. • Recognize that retina is tethered to the optic nerve ­posteriorly and remains tethered in retinal detachments. • Vitreous hemorrhage (*). • Note that vitreous hemorrhage appears as mobile vitreous opacities. • Differentiating vitreous hemorrhage from other vitreous pathology can be difficult. • Vitreous hemorrhage will change in echogenicity as it ages, forming layers. • Lens dislocation (*). Ocular Ultrasound • Note that lens dislocation will appear as an oval structure within the vitreous and a void between the iris on either side. • Partial dislocations can be difficult to diagnose sonographically because the lens is usually in the correct position. • Complete dislocations are obvious due to the lens being found in the vitreous. • Globe rupture (*). • Recognize destruction of globe shape and sonographic landmarks. • Optic nerve sheath diameter. Optic nerve diameter may be measured if there is concern for elevated ICP. The optic nerve sheath diameter should be measured 3 mm from the globe. Normally the diameter should be less than 5 mm. • Measure 3 mm vertically from the globe along optic nerve trajectory. • Measure the optic nerve sheath diameter at this point. 63 64 Clinical Ultrasound: A How-To Guide • Note bulging of the optic disc (*) into the vitreous can be seen with increased ICP/papilledema. SPECIAL CONSIDERATIONS • Consensual papillary response can be demonstrated in patients by exposing uninvolved eye to light and evoking iris constriction under ultrasound visualization. • Place probe indicator temporally so that the macula is always on the side of the screen indicator. • Use the optic nerve as a landmark when evaluating the retina. • Use extreme caution when evaluating patients with potential globe ­rupture; use copious amounts of gel and do not place unnecessary p­ ressure on the eye. • Use of an adhesive dressing on a closed eye increases patient comfort and prevents gel from entering eye. Be sure to lay it flush over the eye and push out underlying air bubbles. 10 Soft Tissue Procedures Mikaela Chilstrom INDICATIONS • Differentiate normal tissue from edema, infection, and focal fluid collections • Determine the nature and extent of soft tissue fluid collections (abscess, cyst, lipoma) • Identify and localize foreign bodies IMAGE ACQUISITION AND INTERPRETATION Equipment • High-frequency linear probe • Endocavity probe for peritonsillar abscesses Preparation • Apply copious gel to affected areas. • Consider water bath or standoff pads (commercial or IV bags) to minimize discomfort from probe pressure. • Use sterile technique with probe cover or large sterile adhesive if using dynamic scanning technique. Soft Tissue Infection • Review normal regional anatomy. • Evaluate area of suspected pathology. • Locate and mark the optimal incision site. Step 1: Review normal regional anatomy • Scan contralateral side or unaffected nearby areas in longitudinal and transverse planes. • Specifically identify normal dermis, subcutaneous tissue, facial planes, muscle, tendons, ligaments, nerves, and vessels. 65 66 Step 2: Evaluate areas of suspected pathology • Scan affected areas in two planes. • Edema: Hypoechoic areas of anechoic fluid separate the subcutaneous tissue creating a “cobblestone” appearance. May be seen in both cellulitis and edema due to other causes. • Cellulitis: Skin and soft tissue will appear ­hyperechoic with blurring or even loss of normal soft tissue landmarks. Abscess Clinical Ultrasound: A How-To Guide Soft Tissue Procedures • Anechoic to mixed echogenic fluid collections surrounded by an often irregular border of hyperechoic tissue (*). • Depending on age and cause, abscess cavity may be round or irregular, which may destroy the fascial planes. • Internal echoes may result from septations or gas. • Apply gentle pressure with probe to move purulent material within abscess. • Identify nearby ligaments, tendons, nerves, lymph nodes, and vessels to avoid during incision and drainage. • Color flow Doppler can assist in defining vascular structures. Step 3: Mark incision site • Estimate the length, width, and depth of a fluid collection. • The ideal ­incision site is the most superficial central area of the abscess. • Mark this area with hash marks in two perpendicular planes to define anesthetic deposition and incision site. 67 68 Clinical Ultrasound: A How-To Guide Foreign Body • • • • Scan the area of interest to localize the foreign body. Measure the size and depth of the foreign body in two planes. Localize the foreign body sonographically with a needle. Extract foreign body. Step 1: Localize the foreign body • Place the probe over the area of interest. • Foreign bodies will generally appear as hyper­ echoic structures with posterior acoustic shadowing. ­Metallic structures may create reverberation or comet tail artifacts. • Retained or infected foreign bodies may be surrounded by hypoechoic fluid. Step 2: Measure the size and depth of the foreign body • Measure the length and width of the foreign body in two dimensions. • Determine the depth of the foreign body. • Identify other pertinent nearby structures tendons, ligaments, bones, nerves, lymph nodes, and vessels. • Foreign bodies that abut or violate important adjacent structures, or are deeply imbedded in soft tissue, should be referred to a specialist for removal. Step 3: Localize the foreign body with needle(s) • Visualize the foreign body in long axis with the probe parallel to the foreign body. • Anesthetize overlying skin and soft tissue. • Advance two different needles under real time in plane visualization to delineate the opposite ends of the foreign body.