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(BQ) Part 2 book Diagnostic imaging - Emergency presents the following contents: Nontraumac (central nervous system, abdomen/pelvis, chest/cardiovascular, musculoskeletal).
Diagnostic Imaging: Emergency fragment and the medial condyle of the humerus This MR was obtained in a 13-year-old baseball pitcher with an acute injury (Right) Anteroposterior radiograph shows reduction and screw fixation of the medial epicondyle avulsion fracture in the same patient (Left) Anteroposterior radiograph shows avulsion of the tip of the medial epicondyle in a 12 year old who started pitching weeks ago, now with elbow pain and presenting for radiographs (Right) Coronal T2WI MR in the same patient shows hyperintense signal throughout the medial epicondyle ossification center The small osseous fragment could not be identified This is an example of Little Leaguer's elbow Part II - Nontrauma Section - Central Nervous System Introduction to CNS Imaging, Nontrauma > Table of Contents > Part II - Nontrauma > Section - Central Nervous System > Introduction to CNS Imaging, Nontrauma Introduction to CNS Imaging, Nontrauma Anne G Osborn, MD, FACR Overview Patients with a number of different nontraumatic disorders of the brain, spine/spinal cord, and head and neck may present in the emergency department While virtually any disease in any body part can be seen in the emergency department, some of the most common urgent entities are discussed in this section Nontraumatic Brain Emergencies Whom to Scan? When to Scan? Head CT scans in nontraumatized patients with CNS-related complaints are commonly obtained in emergency settings and account for 70-80% of all CT requests from emergency departments Prospective studies have revealed that only 8% of such scans reveal clinically significant abnormalities Of these cases, over 95% have positive neurologic findings Growing concerns about both the costs and the radiation exposure that occurs during CT acquisition have prompted attempts to identify clinical variables that are independent predictors of abnormal head CT findings in emergency department patients Six such clinical variables have been identified: (1) Age > 70 years (2) Focal neurologic deficit (3) Altered mental status (4) History of malignancy (5) Nausea &/or vomiting (6) Derangements in coagulation profile 751 Diagnostic Imaging: Emergency Recent studies not support the routine use of brain CT in patients under the age of 70 years for the investigation of uncomplicated headache (i.e., in the absence of additional neurologic findings), migraine-like symptoms, vertigo, dizziness, drug use, blood pressure abnormality, or generalized symptoms such as fatigue or diffuse weakness Presentation at an emergency department with a known patient history of seizure is also not predictive of abnormal head CT findings Nontraumatic Hemorrhage and Vascular Lesions Spontaneous (i.e., nontraumatic) intracranial hemorrhage and vascular brain disorders are second only to trauma as neurologic causes of death and disability When a patient with no history of trauma presents in the emergency department with sudden onset of a neurologic deficit, NECT scans are the most appropriate initial imaging study Challenging questions arise when screening NECT discloses parenchymal hemorrhage What are the potential causes? Is the patient at risk for hematoma expansion? Should further emergent imaging be performed? The most recent American Heart Association/A merican Stroke Association guidelines recommend emergent CT or MR as the initial screening procedure to distinguish ischemic stroke from nontraumatic intracranial hemorrhage If the patient is older than 45 years and has preexisting systemic hypertension, a putaminal, thalamic, or posterior fossa intracranial hemorrhage is almost always hypertensive in origin and does not require additional imaging In contrast, lobar or deep brain bleeds in younger patients or normotensive adults, regardless of age, usually require further investigation Contrast-enhanced CT/MR with angiography may be helpful in detecting underlying abnormalities, such as arteriovenous malformation, neoplasm, and cerebral sinovenous thrombosis A CT angiogram (CTA) is indicated in patients with sudden clinical deterioration and a mixed-density parenchymal hematoma (indicating rapid bleeding or coagulopathy) CTA is also an appropriate next step in children and young/middleaged adults with spontaneous intracranial hemorrhage detected on screening NECT Likewise, CTA is appropriate in patients with aneurysmal, perimesencephalic nonaneurysmal, or convexal subarachnoid hemorrhage If a CTA is negative, emergency MR is rarely necessary in patients with unexplained “spontaneous” intracranial hemorrhage (sICH), although a follow-up nonemergent MR with and without contrast can be very useful Evidence for prior hemorrhage on T2* sequences (GRE or SWI) can be very helpful in narrowing the differential diagnosis Multifocal “black dots” in elderly patients with sICH is typical for chronic hypertensive encephalopathy and amyloid angiopathy (CAA) Basal ganglia and cerebellar “black dots” are common in chronic hypertension but rare in CAA Conversely, peripheral (cortical, meningeal) “blooming black dots” on T2* are more common in CAA Strokes “Stroke” is a generic term that describes a clinical event characterized by sudden onset of a neurologic deficit However, not all strokes are the same! Stroke syndromes have significant clinical and pathophysiological heterogeneity Arterial ischemia/infarction is by far the most common cause of stroke, accounting for 80% of all cases The remaining 20% of strokes are mostly hemorrhagic, divided among primary “spontaneous” (nontraumatic) intracranial hemorrhage, nontraumatic subarachnoid hemorrhage, and venous occlusions As the clinical diagnosis of acute stroke is inaccurate in 15-20% of cases, imaging has become an essential component of rapid stroke triage When and how to image patients with suspected acute stroke varies from institution to institution Protocols are based on elapsed time since symptom onset, availability of emergent imaging with appropriate software reconstructions, preferences of clinician (and radiologist), and availability of neurointervention There are four “must know” questions in stroke triage that must be answered quickly and accurately: (1) Is intracranial hemorrhage or a stroke “mimic” present? (2) Is a large vessel occluded? (3) Is part of the brain irreversibly injured? (4) Is there a clinically relevant “penumbra” of ischemic but potentially salvageable tissue? The primary goal of “brain attack” protocols is to distinguish “bland” or ischemic stroke from intracranial hemorrhage and to select/triage patients for possible reperfusion therapies Most protocols begin with emergency NECT to answer the first “must know” question: Is intracranial hemorrhage or a stroke mimic present? Once intracranial hemorrhage is excluded, presence or absence of a major vessel occlusion can be determined noninvasively with CTA The third and fourth questions can be answered with either CT or MR perfusion P.II(1):3 Infections The role of medical imaging in the emergent evaluation of a possible intracranial infection ideally should be supportive, not primary But in many health care facilities worldwide, a triage of acute CNS disease frequently uses brain imaging as an initial noninvasive “screening procedure.” 752 Diagnostic Imaging: Emergency Meningitis is a clinical laboratory diagnosis, not a radiologic one NECT scans in meningitis can be normal or show only mild ventricular enlargement Large ventricles with blurred margins on NECT scans indicate acute obstructive hydrocephalus with accumulation of extracellular fluid in the deep periventricular white matter Bone CT should be carefully evaluated for sinusitis and otomastoiditis Encephalitis can be sporadic or epidemic NECT scans in the most common nonepidemic encephalitis, i.e., herpes simplex encephalitis, may be normal or show only hypodensity with mild mass effect in one or both temporal lobes Patients with suspected encephalitis are best evaluated with MR (including FLAIR and diffusion-weighted sequences) Brain abscesses and empyemas are rare but potentially life-threatening CNS infections Intraventricular rupture of a brain abscess can be a catastrophic event All these are serious disorders that are best evaluated with contrast-enhanced MR (including FLAIR and diffusion-weighted sequences) Contrast-enhanced CT can also be performed if a screening NECT is suggestive of either diagnosis Acute Toxic-Metabolic Derangements A number of toxic and metabolic disorders present in the emergency department In the absence of focal neurologic deficit or altered mental status, emergent imaging is usually not indicated There are some notable exceptions, e.g., pregnant patients with preeclampsia or eclampsia or hypertensive patients on chemotherapy Posterior reversible encephalopathy syndrome (PRES) is common in both scenarios NECT scan is a good initial screening procedure If it's normal or equivocal, MR is more sensitive in subtle or atypical cases Seizures Patients with first-time seizures and no neurologic deficit usually not require emergent neuroimaging A “screening” NECT scan is relatively useless as subtle abnormalities are easily overlooked Patients with recurrent, often drug-resistant epilepsy are common ER visitors Without trauma-associated brain injury, emergent neuroimaging is rarely indicated Complex febrile seizures are a common diagnosis in the pediatric emergency department Recent studies have shown a low likelihood of intracranial infections and abnormal neuroimaging findings Dizziness Adults triaged to the ED with complaints of dizziness, vertigo, or imbalance pose a challenge to physicians While dizziness in the ED is generally benign, a substantial fraction of patients harbor serious neurologic disease such as stroke, intracranial hemorrhage, transient ischemic attack, seizure, brain tumor, demyelinating disease, and CNS infection Older age, a chief complaint of imbalance, and focal neurologic abnormality are all independently associated with serious neurologic diagnoses and may deserve emergent imaging Imaging is usually negative in solated dizziness without other abnormalities Head and Neck Emergencies Patients may present to the emergency department with a wide variety of nontraumatic infectious, inflammatory, and neoplastic conditions affecting the head and neck Acute conditions that require emergent imaging are generally restricted to trauma and suspected infections Some can be potentially life threatening Oral cavity infections, tonsillitis and peritonsillar abscess, sialadenitis, parotiditis, thrombophlebitis, periorbital and orbital cellulitis, infectious cervical lymphadenopathy, epiglottitis, invasive fungal sinusitis, and deep neck abscess all require rapid diagnosis and treatment CT is the first-line imaging modality in the emergency setting, and MR plays an important secondary role Nontraumatic Emergencies Involving the Spine/Spinal Cord While patients with back pain are common ER visitors, they generally not require emergent imaging unless a focal neurologic deficit is present True nontraumatic spinal emergencies are rare but represent a potential loss of function if not treated promptly and properly Patients with acute myelopathy, suspected infection, or cord ischemia as well as individuals with a known malignancy and sudden onset of a neurologic deficit all require emergent imaging MR is generally the procedure of choice A new imaging sequence—diffusion tensor imaging—can be very helpful in early detection of cord ischemia Selected References Balestrini S et al: Emergency room access for recurring seizures: when and why Eur J Neurol Epub ahead of print, 2013 Boyle DA et al: Clinical factors associated with invasive testing and imaging in patients with complex febrile seizures Pediatr Emerg Care 29(4):430-4, 2013 Wang X et al: Head CT for nontrauma patients in the emergency department: clinical predictors of abnormal findings Radiology 266(3):783-90, 2013 Kelley BC et al: Spinal emergencies J Neurosurg Sci 56(2):113-29, 2012 Navi BB et al: Rate and predictors of serious neurologic causes of dizziness in the emergency department Mayo Clin Proc 87(11):1080-8, 2012 Scheinfeld MH et al: Teeth: what radiologists should know Radiographics 32(7):1927-44, 2012 753 Diagnostic Imaging: Emergency Capps EF et al: Emergency imaging assessment of acute, nontraumatic conditions of the head and neck Radiographics 30(5):1335-52, 2010 Erratum in: Radiographics 31(1):316, 2011 Crocker M et al: An extended role for CT in the emergency diagnosis of malignant spinal cord compression Clin Radiol 66(10):922-7, 2011 Jagoda A et al: The emergency department evaluation of the adult patient who presents with a first-time seizure Emerg Med Clin North Am 29(1):41-9, 2011 10 Ludwig BJ et al: Diagnostic imaging in nontraumatic pediatric head and neck emergencies Radiographics 30(3):78199, 2010 11 Hardy JE et al: Computerized tomography of the brain for elderly patients presenting to the emergency department with acute confusion Emerg Med Australas 20(5):420-4, 2008 Brain Aneurysmal Subarachnoid Hemorrhage > Table of Contents > Part II - Nontrauma > Section - Central Nervous System > Brain > Aneurysmal Subarachnoid Hemorrhage Aneurysmal Subarachnoid Hemorrhage Perry P Ng, MBBS (Hons), FRANZCR Anne G Osborn, MD, FACR Key Facts Terminology SAH caused by ruptured aneurysm (aSAH) Saccular (SA) > > dissecting aneurysm (DA) Imaging CT/CTA Hyperdense sulci on NECT Distribution varies with aneurysm location Suprasellar cistern (IC-PCoA, ACoA aneurysms) Sylvian fissure (MCA bifurcation) Prepontine, CPA cisterns (PICA, BA bifurcation SA or vertebral DA) CTA 90-95% positive if aneurysm ≥ mm MR/MRA FLAIR hyperintense sulci, cisterns (nonspecific) TOF MRA 85-95% sensitive for aneurysms ≥ mm DSA Used if CTA negative Endovascular treatment Top Differential Diagnoses Nonaneurysmal SAH “Pseudo-SAH” Reversible cerebral vasoconstriction syndrome (RCVS) Clinical Issues Sudden onset severe headache “Thunderclap/worst headache of life” 50% mortality Vasospasm 1-3 weeks post aSAH 20% rebleed within 1st weeks Treatment Clipping vs coil embolization (“coiling”) Diagnostic Checklist Diffuse low-density brain makes normal arteries look hyperdense, can mimic aSAH! 754 Diagnostic Imaging: Emergency (Left) Axial graphic through the midbrain depicts SAH in red throughout the basal cisterns Given the diffuse distribution of SAH without focal hematoma, statistically the most likely location of the ruptured aneurysm is the ACoA (Right) Series of axial NECT scans shows the typical appearance of aneurysmal SAH Acute subarachnoid blood is seen as hyperdensity in the basal cisterns, sylvian fissures, perimesencephalic cisterns, and interhemispheric fissure Ruptured ACoA aneurysm was found on CTA (not shown) (Left) NECT scan shows diffuse basilar SAH with more focal clot in the right anteromedial temporal lobe and along the right side of the suprasellar cistern (Right) 3D SSD of the right ICA angiogram in the same patient shows a large trilobed IC-PCoA aneurysm P.II(1):5 TERMINOLOGY Abbreviations Aneurysmal subarachnoid hemorrhage (aSAH) Definitions Extravasation of blood into subarachnoid space Usually from ruptured saccular aneurysm Less common: Intracranial dissecting aneurysm IMAGING 755 Diagnostic Imaging: Emergency General Features Best diagnostic clue Hyperdense basal cisterns, sulci on NECT Location Suprasellar, basal, sylvian, interhemispheric cisterns ± intraventricular hemorrhage (IVH) aSAH distribution depends on location of saccular aneurysm (SA) aSAH highest near site of rupture Anterior communicating artery (ACoA) aneurysm → anterior interhemispheric fissure Middle cerebral artery (MCA) aneurysm → sylvian fissure Basilar tip, superior cerebellar artery (SCA), posterior inferior cerebellar artery (PICA) SA, or vertebral artery (VA) dissecting aneurysm (DA) → prepontine cistern, foramen magnum, 4th ventricle “Culprit” aneurysm sometimes seen as filling defect within hyperdense aSAH SAs typically located at bifurcation points along intradural ICA, circle of Willis (COW), MCA 90% located on anterior circulation: ACoA, posterior communicating artery (PCoA), MCA, carotid terminus, carotid-ophthalmic, superior hypophyseal 10% on posterior circulation: Basilar tip, PICA, anterior inferior cerebellar artery (AICA), SCA DAs: Intradural V4 VA segment most common Blood-blister aneurysm (BBA) Dorsal supraclinoid ICA Rarely MCA, basilar artery CT Findings NECT 95% positive in 1st 24 hours, < 50% by week “Effaced” sylvian fissure if subacute, filled with isodense SAH Hydrocephalus common, may occur early ± intraparenchymal hemorrhage at site of ruptured aneurysm CTA 90-95% positive if aneurysm ≥ mm MR Findings T1WI Acute aSAH is isointense to CSF CSF may appear mildly hyperintense (“dirty”) T2WI Difficult to see on T2WI (hyperintense), GRE FLAIR Hyperintense More sensitive than CT but less specific DWI May see foci of restricted diffusion if vasospasm MRA TOF MRA 85-95% sensitive for aneurysms ≥ mm Angiographic Findings Conventional “4-vessel angiogram” = gold standard Must image Both ICA circulations Both VAs or dominant VA + reflux to contralateral PICA SA Saccular outpouching at arterial branch point Look for Murphy teat = site of rupture Look for additional aneurysms (20% multiple) If > aneurysm, then biggest, most irregular ± adjacent vasospasm is likely source of bleed DA 756 Diagnostic Imaging: Emergency Irregular ± dilated or stenotic V4 segment of VA BBA Smooth/irregular bleb/dome-shaped outpouching Not associated with major vessel branch point Most common along supraclinoid ICA DSA negative in 15% of aSAH; repeat positive < 5% Evaluate ECAs (to exclude dural AV fistula [dAVF]) SA may not be seen on initial DSA if optimal projection not obtained, spontaneous partial or complete aneurysm thrombosis, &/or presence of vasospasm Consider repeating DSA in 5-7 days Imaging Recommendations Best imaging tool NECT + multiplanar CTA Protocol advice Proceed to DSA if NECT consistent with aSAH but CTA negative Consider MR if DSA + CTA negative DIFFERENTIAL DIAGNOSIS Nonaneurysmal SAH Perimesencephalic SAH Small SAH, localized to interpeduncular cistern Presumed venous etiology with low recurrence rate Traumatic subarachnoid hemorrhage Adjacent to contusions, subdural hematomas Rarely from intracranial dissection or rupture of traumatic pseudoaneurysm Subarachnoid hemorrhage, NOS Vascular malformation: Arteriovenous malformation (AVM), cavernous hemangioma Reversible Cerebral Vasoconstriction Syndrome (RCVS) Clinical: “Thunderclap” headache SAH typically in cortical sulci vs basal cisterns with aSAH “Pseudo-SAH” Hypodense brain: Severe cerebral edema Hyperdense CSF: Intrathecal contrast; meningitis P.II(1):6 PATHOLOGY General Features Etiology Saccular aneurysms Berry aneurysms: Congenital deficiency of internal elastic lamina and tunica media at arterial branch points → focal vessel wall weakness ↑ risk: Familial intracranial aneurysms (5% of cases), adult polycystic kidney disease, aortic coarctation May be related to high-flow arteriopathy along feeding vessel of AVM or, less commonly, dAVF ↑ aneurysm rupture risk if female, smoker, HTN Fusiform aneurysms Dissection from trauma, hypertension, ASVD Underlying arteriopathy including fibromuscular dysplasia (FMD), Marfan, Ehlers-Danlos, infection Mycotic Blood-blister aneurysm: All layers absent (contained in fibrous cap) Associated abnormalities Vasospasm Caused by blood breakdown products, apolipoprotein E genotype, endothelin-1 release from CSF leukocytes 70% develop angiographic evidence of vasospasm 757 Diagnostic Imaging: Emergency 30% have clinically apparent vasospasm Starts ˜ day 3-4 post SAH; peaks ˜ 7-9 days, lasts ˜ 12-16 days Cerebral salt-wasting syndrome Excessive renal Na+ excretion → hyponatremia, hypovolemia Terson syndrome Intraocular (retinal, vitreous) hemorrhage associated with SAH secondary to rapid ↑ intracranial pressure Staging, Grading, & Classification Clinical grading: Hunt and Hess (H&H) grade 0-5 0: No SAH (unruptured aneurysm) 1: No symptoms, minimal headache, slight nuchal rigidity 2: Moderate to severe headache, nuchal rigidity No neurologic deficit except CN palsy 3: Drowsy, minimal neurologic deficit 4: Stuporous, moderate/severe hemiparesis 5: Coma, decerebrate rigidity, moribund appearance WFNS clinical grading system: Based on GCS and presence/absence of major focal neurological deficit Fisher CT grading 1: No SAH visible 2: Diffuse, thin layer (< mm) 3: Localized clot or thick layer (> mm) 4: Intraventricular blood Gross Pathologic & Surgical Features Blood in basal cisterns, sulci, and ventricles CLINICAL ISSUES Presentation Most common signs/symptoms Sudden “thunderclap/worst headache of life” 10% preceded by “sentinel hemorrhage” = self-limiting SAH + headache in preceding days/weeks Demographics Age Peak = 40-60 years Gender M:F = 1:2 Epidemiology Aneurysms cause 85% of spontaneous SAHs Incidence ˜ 9.9 per 100,000 population Natural History & Prognosis 50% mortality; 20% rebleed within 1st weeks Clinical outcome inversely proportional to initial H&H or WFNS grade Vasospasm + ischemia → delayed morbidity, mortality Severity correlates with amount of SAH (Fisher CT grade); inverse correlation with patient age 90% hydrocephalus at presentation ˜ 10% require permanent CSF diversion Treatment Ruptured aneurysm Microneurosurgical clipping Proven effective over decades but invasive, higher morbidity/mortality compared with coiling study: Death or dependence at year = 23.7% with coiling vs 30.7% with clipping Coil embolization (“coiling”), if anatomy favorable Platinum coils ± bioactive coating to reduce recurrence rate Aneurysm recurrence > surgical clipping but low risk of recurrent SAH Vasospasm Ca++ antagonists, “triple-H” therapy (hypervolemia, hemodilution, hypertension) Endovascular: Intraarterial Ca++ antagonist (“chemical angioplasty”), balloon angioplasty 758 Diagnostic Imaging: Emergency Hydrocephalus Temporary or permanent CSF diversion Cerebral salt-wasting syndrome Na+ tablets or IV hypertonic saline DIAGNOSTIC CHECKLIST Consider Nonaneurysmal SAH if characteristic blood distribution (e.g., perimesencephalic SAH, RCVS) Look for multiple aneurysms and decide which most likely bled Image Interpretation Pearls Isodense SAH: Anterior 3rd ventricle and temporal horns are only CSF density structures at base of brain; absence of sylvian fissure(s) SELECTED REFERENCES Farzad A et al: Emergency diagnosis of subarachnoid hemorrhage: an evidence-based debate J Emerg Med 44(5):104553, 2013 Froehler MT: Endovascular treatment of ruptured intracranial aneurysms Curr Neurol Neurosci Rep 13(2):326, 2013 P.II(1):7 Image Gallery (Left) NECT scan in a patient with sudden onset of the “worst headache of my life” shows aSAH in the suprasellar cistern and sylvian fissures A “filling defect” is present within the blood in the anteroinferior aspect of the interhemispheric fissure (Right) CTA in the same case shows a mm saccular aneurysm arising from the anterior communicating artery 759 Diagnostic Imaging: Emergency (Left) Sagittal T1WI illustrates typical findings of acute aneurysmal SAH Note “dirty” CSF that appears isointense with adjacent brain The normal basilar artery “flow void” is surrounded by the SAH (Right) Axial T1WI in the same case shows a nice contrast between the isointense (with brain) “dirty” CSF and the more normal-appearing hypointense (“dark”) CSF in the cistern and temporal horns (Left) T2WI in the same patient shows that the hyperintense SAH is difficult to distinguish from the normal “bright” CSF The SAH is very slightly less hyperintense than the adjacent CSF (Right) Normal CSF suppresses on FLAIR FLAIR scan in the same case shows CSF in the suprasellar cistern is abnormally hyperintense Sulcal-cisternal hyperintensity is also seen in the left perimesencephalic and superior cerebellar cisterns as well as the parietooccipital subarachnoid spaces Nonaneurysmal Perimesencephalic SAH > Table of Contents > Part II - Nontrauma > Section - Central Nervous System > Brain > Nonaneurysmal Perimesencephalic SAH Nonaneurysmal Perimesencephalic SAH Gary M Nesbit, MD Anne G Osborn, MD, FACR Key Facts 760 Diagnostic Imaging: Emergency Metaphyseal fractures from slightly oversized press-fit components Fractures occur more frequently in cementless press-fit than cemented femoral components Diaphyseal fractures most frequently seen with longstem components (straight, extending down anteriorly bowed femur) Dislocation Positional: Joint placed beyond expected range Occurs with THA in forced ad- or abduction Incorrect positioning of components Stress shielding: Altered weight-bearing through implant reduces stress on regions of bone → resorption of bone → relative lucency Massive osteolysis Particles of critical size → inflammatory reaction Pseudotumor associated with metal-on-metal THA Possibly a toxic reaction to metal wear debris Possibly a hypersensitivity reaction to normally expected amount of metal debris CLINICAL ISSUES Natural History & Prognosis 80% of THAs last 20 years without revision Uncemented acetabular components with polyethylene liners undergo silent lysis and merit regular long-term radiological review Rate of development of abnormal soft tissue reaction and mass in metal-on-metal THA is unknown Conservative estimate of 1%; likely to ↑ significantly as these relatively new implants age DIAGNOSTIC CHECKLIST Consider Watch for subsidence of components to indicate loosening, even without obvious lucency Compare follow-up image with index radiograph for change in component position With dislocation, search for malposition of components as a cause With osteolysis, search for evidence of particle disease SELECTED REFERENCES Awan O et al: Imaging evaluation of complications of hip arthroplasty: review of current concepts and imaging findings Can Assoc Radiol J Epub ahead of print, 2013 Bestic JM et al: Current concepts in hip arthroplasty imaging: metal-on-metal prostheses, their complications, and imaging strategies Semin Roentgenol 48(2):178-86, 2013 Campe CB et al: MR imaging of metal-on-metal hip prostheses Magn Reson Imaging Clin N Am 21(1):155-68, 2013 Chang EY et al: Metal-on-metal total hip arthroplasty: symptoms correlate with MR imaging findings? Radiology 265(3):848-57, 2012 Roth TD et al: CT of the Hip Prosthesis: Appearance of Components, Fixation, and Complications RadioGraphics 32:1089-1107, 2012 P.II(4):525 Image Gallery 1555 Diagnostic Imaging: Emergency (Left) Groin lateral graphic shows the expected anterior tilt (anteversion) of the acetabular component The angle on the femoral component describes the neck-shaft angle (Right) Groin lateral view of a THA in a patient with recurrent dislocations shows retroversion of the acetabular component (compare with previous image) One cannot determine retroversion vs anteversion on AP radiograph; groin lateral or CT is required Retroversion puts a THA at risk for dislocation (Left) AP radiograph shows a hip dislocation The acetabular component shows normal lateral tilt However, there is excessive version (opening either anterior or posterior) The groin lateral (not shown) confirmed excessive anteversion While anteversion of the cup is expected, this degree puts the hip at risk for dislocation (Right) AP radiograph shows gross loosening of the cup with superior subsidence (note distance from original site ) The cup is fractured and shows a wide lucency relative to cement 1556 Diagnostic Imaging: Emergency (Left) AP radiograph shows moderate cortical and endosteal hypertrophy about the tip of the stem of a cementless femoral component There is also a sclerotic line but no lucent bone-component interface This appearance is normal for a cementless component (Right) AP radiograph shows excessive cortical and endosteal hypertrophy bridging the medullary canal Additionally, there is a lucency > mm surrounding the component These findings are typical of loosening P.II(4):526 (Left) AP radiograph shows a THA with uncommonly obvious findings of infection There is air in the soft tissues as well as fluffy immature heterotopic bone formation An infected arthroplasty usually appears normal; any clinical suspicion requires aspiration (Right) Coronal T2WI MR shows ↓ SI antibiotic beads placed in the defect following explant of an infected THA Unfortunately, the treatment has not been effective, indicated by ↑ SI throughout the remaining acetabulum and shaft 1557 Diagnostic Imaging: Emergency (Left) AP radiograph shows metaphyseal lucency extending into the greater trochanter, noted several years following THA This is the typical location of stress shielding and should not be misinterpreted as infection or a lytic lesion (Right) AP radiograph shows polyethylene wear, demonstrated by thinning of the distance between the metal cup and head superiorly compared with the distance inferiorly This wear results in particle disease and lysis (Left) Frog leg lateral radiograph shows an expanded lytic lesion involving the proximal metaphysis of the femur There is no other abnormality seen, and the AP radiograph was normal (not shown) This leaves a wide differential diagnosis, including tumor (Right) Groin lateral, same case, does not show the lytic lesion as well, but polyethylene wear is readily seen, as outlined by the arrows With a source of particles demonstrated in this manner, the lytic lesion is likely a related osteolysis P.II(4):527 1558 Diagnostic Imaging: Emergency (Left) Coronal reformat bone CT shows a large acetabular region of lysis as well as evidence of polyethylene wear (offset of head in cup ) The radiograph (not shown) was difficult to evaluate; CT adds important information regarding extent of osteolysis, which results in better planning of a substantial revision (Right) Coronal bone CT shows extensive thinning of cortex with prosthetic loosening (note the wide bone-cement lucency), as well as fracture Neither subtlety was seen on radiograph (Left) Coronal T1WI MR shows bilateral THAs and an enormous fluid collection in the right iliopsoas bursa Concern was for infection vs synovitis (Right) Axial bone CT confirms a fluid collection in the iliacus bursa Aspiration yielded thick gelatinous material & debris-laden macrophages Debris formed from THA polyethylene wear and caused a synovitis, which decompressed into the iliopsoas bursa Prominent thinning of the iliac wing may be due to pressure rather than particle lysis 1559 Diagnostic Imaging: Emergency (Left) AP radiograph shows a metal-on-metal prosthesis ; note the absence of polyethylene liner This patient had pain, which is not explained by poorly positioned components (Right) Axial CECT shows mild enhancement of an inhomogeneous iliacus mass Extensive biopsy showed only debris and necrotic tissue Such necrotic masses are being shown more frequently by CT or MR in metal-on-metal THAs; cross-sectional imaging should be suggested with this type of THA and unexplained pain Knee Implant > Table of Contents > Part II - Nontrauma > Section - Musculoskeletal > Orthopedic Hardware Complications > Knee Implant Knee Implant Key Facts Terminology Total knee arthroplasty (TKA): Replacement of femoral, tibial, and patellar articular surfaces Imaging Component size matched to knee Initial placement of components Femoral: 5° ± 5° to long axis of femoral axis on lateral Femoral: 4-7° valgus on AP Tibial: 90° ± 5° to long axis of tibial shaft on AP Tibial: Component plus polyethylene → 10° posterior tilt Rotational malalignment Radiograph only shows significant malalignment; CT improves accuracy Patellar button dislocation from cement or metal backing Tibial polyethylene may dislocate from metal tray Stress shielding: Occurs in anterior and mid femoral metaphysis, seen on lateral radiograph Loosening: Change in position (tilt or subsidence) Patellar button usually subsides superiorly Tibial component subsides inferiorly, usually with medial trabecular compression Clinical Issues Most common arthroplasty performed today Diagnostic Checklist Keep in mind shape of polyethylene components; lucency of this shape in wrong location is hint of dislocation Periprosthetic fractures are easily missed; include them in your search pattern Increased risk for periprosthetic fracture with osteoporosis &/or tibial tubercle transfer 1560 Diagnostic Imaging: Emergency (Left) Lateral radiograph shows a normal total knee arthroplasty (TKA) The sizing of the components is correct Alignment is normal Note the slight posterior tilt of the tibial component as well as the differential thickness of the anterior polyethylene compared with posterior (Right) Lateral radiograph shows anterior rather than posterior tilt of the tibial component The normal tibial plateau has a posterior tilt of approximately 7°, and the arthroplasty should approximate this angulation (Left) AP radiograph shows a normal unicondylar knee arthroplasty These components may be chosen when there is no significant arthritis in the remaining compartments Unicondylar arthroplasties are not used in patients with inflammatory arthritis (Right) Lateral radiograph, same case, shows that the femoral implant is placed on the mid and posterior weight-bearing portions of the condyle; there is a notch formed in the anterior portion of the condyle to reduce the likelihood of patellar impingement P.II(4):529 TERMINOLOGY Definitions Total knee arthroplasty (TKA): Replacement of femoral, tibial, and patellar articular surfaces Nonconstrained components Generally, posterior cruciate ligament is retained Other soft tissues, including collateral ligaments, provide stability 1561 Diagnostic Imaging: Emergency Concave polyethylene adds some constraint Semiconstrained components Usually longstemmed Peg extends from femoral side into central cylinder on tibial side; allows some rotation Do not misinterpret lucency around peg as loosening of component Single compartment (unicompartmental) implant: Medial, lateral, or patellofemoral Considered when only a single compartment involved with significant osteoarthritis Not used if underlying process is inflammatory IMAGING Radiographic Findings Component size matched to knee Oversized femoral component seen as gap between anterior cortex and flange Blocks full range of motion Undersized femoral component → notching of anterior femoral cortex At risk for fracture Oversized tibial component → overhanging edge Irritates adjacent tendons and ligaments Undersized tibial component Subsidence into tibia, eventual loosening Initial placement of components Femoral component 5° ± 5° to long axis of femoral axis on lateral 4-7° valgus on AP Tibial component 90° ± 5° to long axis of tibial shaft on AP Component plus polyethylene → 10° posterior tilt Metal component may not appear tilted; made up by differential thickness of polyethylene If no posterior tilt, blocks full flexion Rotational malalignment External rotation of tibial component → patellar dislocation, eccentric wear Implant fracture Fracture (fx) of metallic backing ring, dissociates from patella Indicates likely polyethylene fx or dislocation Fragments may line synovium or joint components: “Metallosis” Dislocation Patellar button dislocated from cement or metal backing Seen as convex lucency offset from patella Patellar button may take a ring or partial ring of metallic backing material with it Tibial polyethylene may dislocate from metal tray Displaces into joint, locking it Stress shielding Occurs in anterior and mid femoral metaphysis, seen on lateral radiograph Bone resorption and lucency at this site Streaming ↑ bone density extends from posterior femoral peg to posterior metaphyseal cortex Loosening Change in position (tilt or subsidence) Patellar button usually subsides superiorly Tibial component subsides inferiorly, usually with medial compression ≥ mm lucency at bone-cement or bone-component interface Component wear Asymmetric width of tibial polyethylene, medial compared with lateral (asymmetry normally expected anterior vs posterior) Particle disease Morphology Focal lytic bone destruction; may mimic tumor 1562 Diagnostic Imaging: Emergency May extend along screw, with bone destruction appearing more elongated May extend into soft tissues as mass or bursal collection Search for particle source to establish diagnosis Polyethylene dislocation or wear Metallosis (bead shedding or other metal debris) Periprosthetic fracture Most frequent fracture: Patella (usually transverse) Thin bone, made even thinner and devascularized by osteotomy for patellar button Proximal tibial metaphyseal fracture Initial buckle, followed by linear sclerosis Fracture risk increased with prior tibial tubercle transfer CT Findings Evaluation of rotational malalignment Femoral component: Angle of (1) epicondylar axis on femur (line from lateral epicondylar prominence to medial sulcus) & (2) line crossing posterior condylar surfaces 0° ± 3° Tibial component: Angle of (1) line perpendicular to line extending from center of tibial stem to medial 1/3 of tibial tuberosity & (2) posterior condylar line (or line drawn between tibial fixation pins) 0° ± 3° Evaluation of periprosthetic loosening, osteolysis, fx Used to evaluate location of lysis and adequacy of bone stock prior to revision MR Findings Evaluation of soft tissue or bursal mass, usually related to particle disease T1WI: ↓ regions of synovitis and lysis in bone STIR: ↑ SI synovitis, mass, bursal, bone lesions CLINICAL ISSUES Natural History & Prognosis Revision-free survival of modern TKAs: 95% SELECTED REFERENCES Plodkowski AJ et al: Lamellated hyperintense synovitis: potential MR imaging sign of an infected knee arthroplasty Radiology 266(1):256-60, 2013 P.II(4):530 Image Gallery (Left) Lateral radiograph shows an unstable TKA This prosthesis spares the posterior cruciate ligament, but it must be ruptured in this case (Right) Lateral radiograph shows typical stress shielding, considered normal There is resorption of bone in the anterior and mid femoral metaphysis , while new bone is laid down posteriorly, extending from the peg to the posterior cortex There is no associated pain or risk of failure The lucency must not be misinterpreted as 1563 Diagnostic Imaging: Emergency osteolysis (Left) AP radiograph shows a thin lucency at the bone-component interface This does not qualify as loosening but should be watched for progression (Right) AP radiograph shows a cemented TKA that is grossly loose There is abnormal tilt and a wide bone-cement lucency There is bead shedding as well Note the wide polyethylene compared with that on the previous image; different widths are chosen based on stability requirements (Left) Lateral radiograph shows a failed semiconstrained prosthesis There is a loose screw More importantly, the constraining peg has dislocated, along with the plate by which it attaches to the tibial tray This plate also attached to the tibial polyethylene, which has dislocated anteromedially into the soft tissues (Right) AP radiograph, same case, shows a loose screw in the soft tissues and a portion of metal superimposed over the medial joint, which is abnormal P.II(4):531 1564 Diagnostic Imaging: Emergency (Left) Lateral radiograph shows the lucent patellar button to be dissociated from the patella and inferiorly displaced This abnormality is easily missed and depends on noting a subtle lucency in an abnormal location (Right) Axial radiograph of the patellofemoral joint, same case, shows the entire patellar button is dislocated relative to the patella The cement has sheered off the bone, making visualization of the lucent patellar button easier (Left) AP radiograph shows lateral subluxation of the tibia with medial gapping There is a relative lucency wedged medially between the femur and tibia This is the polyethylene tibial liner, which has loosened and dislocated from the tibial tray (Right) AP radiograph shows a unicondylar knee implant with metal on metal This is abnormal and indicates either complete wear or dislocation of the polyethylene component 1565 Diagnostic Imaging: Emergency (Left) AP radiograph shows a rounded metallic density located superior to the patella, representing dissociation of the metal backing from the patellar button (Right) Lateral radiograph, same case, confirms the superior displacement of the dissociated backing There are areas of faint deposition of metal, along the synovium anteriorly and along the tibial polyethylene The patellar button will go on to fail further; the metallosis will lead to a significant synovitis P.II(4):532 (Left) AP radiograph shows a lytic lesion in the sub-implant bone Considerations include preexisting subchondral cyst or lytic lesion, such as metastasis, but in this case it is due to particle disease The source of the particles is worn polyethylene; note the differential thickness (Right) AP radiograph shows massive osteolysis occurring around the medial tibial screw in this TKA Additionally, there is a subtle decrease in height of the polyethylene on the tibial tray , indicating wear 1566 Diagnostic Imaging: Emergency (Left) Coronal CT, same case, is obtained for further evaluation It shows the degree of osteolysis surrounding the medial screw The lysis is much more extensive than would be expected based only on the radiograph Note the relationship to the tibial screw; the particles are forced down along the screw track (Right) Sagittal bone CT, same case, shows a pathologic fracture at the posterior cortex along with a small amount of fracture callus , indicating subacuity (Left) AP radiograph demonstrates a TKA and large adjacent soft tissue mass The TKA shows mild thinning of the medial polyethylene (Right) Axial NECT, same case, shows the mass along with a large lytic osseous lesion Femoral component is neutral relative to the surgical epicondyle axis, but the tibial component was externally rotated (not shown) Thus, particle sources may arise from either patellar or tibial polyethylene The mass was necrotic granulomatous tissue, proven by biopsy P.II(4):533 1567 Diagnostic Imaging: Emergency (Left) Lateral radiograph shows a large, expansile mass that has destroyed the majority of the posterior distal left femur The smooth, sclerotic border and marginal heterotopic ossification suggests that this is a slowly progressive process Biopsy confirmed particle disease (Right) Lateral radiograph shows a displaced patellar fx following placement of TKA The patella is at risk due to the osteotomy for placement of the patellar button, which causes devascularization and thinning of the bone (Left) AP radiograph shows TKA in osteoporotic bone There is linear sclerosis in the tibial metaphysis, which is diagnostic of an insufficiency fracture (Right) Lateral radiograph confirms the linear nature of the sclerosis Periprosthetic fractures are difficult to diagnose in the acute situation but should be sought and diagnosed once this impaction and healing sclerosis is demonstrated Such fractures occur following TKA placement, particularly when the bone is osteoporotic and the patient increases activity 1568 Diagnostic Imaging: Emergency (Left) Lateral radiograph shows a TKA but also shows a tibial tubercle transfer Additionally, there is linear sclerosis seen just distal to the transferred tubercle This represents a periprosthetic insufficiency fracture There is added risk for development of a fracture when the patient has also had a tibial tubercle transfer, as in this case (Right) Lateral radiograph of a patient with TKA shows intraarticular density , which distorts Hoffa fat pad This proved to be arthrofibrosis 1569 ... 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