FUNDAMENTALS OF SKELETAL RADIOLOGY Fourth Edition Clyde A. Helms, MD Professor of Radiology and Orthopaedic Surgery Department of Radiology Duke University School of Medicine Durham, North Carolina 1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899 FUNDAMENTALS OF SKELETAL RADIOLOGY, ISBN: 978-1-4557-5154-9 FOURTH EDITION Copyright © 2014 by Saunders, an imprint of Elsevier Inc. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/ permissions. 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Previous editions copyrighted 1989, 1995, 2005 ISBN: 978-1-4557-5154-9 Content Strategy Director: Mary Gatsch Senior Content Strategist: Don Scholz Content Development Specialist: Kelly McGowan Publishing Services Manager: Patricia Tannian Senior Project Manager: John Casey Designer: Steven Stave Printed in China Last digit is the print number: 9 8 7 6 5 4 3 2 1 C H A P T E R 1 Unnecessary Examinations Before beginning to learn how to interpret There is virtually no finding on a skull series that pathologic skeletal films, it is important to briefly will alter the next step in the patient’s workup. consider unnecessary skeletal radiographic ex- Presence or absence of a fracture should not in- aminations. Dr. Ferris Hall from Boston first fluence whether the patient receives a computed brought to my attention the idea that just be- tomography (CT) scan or a magnetic resonance cause we could x-ray something didn’t mean that imaging (MRI) examination. A CT or MRI scan we should. His article titled “Overutilization of is obtained for other reasons: continued uncon- Radiologic Examinations” in the August 1976 sciousness or focal neurologic signs. The plain issue of Radiology1 details many examples of over- films only delay the eventual diagnosis, and in a use and misuse of radiologic examinations. This patient with a subdural or an epidural hema- article, even though it is more than 35 years old, toma, that delay could be fatal.3 The mortality and a similar one by Dr. Herbert Abrams in the from intracranial bleeding is significantly in- New England Journal of Medicine2 should be man- creased as the time to surgical decompression is datory reading for every intern before he or she increased; therefore any delay caused by obtain- begins to order examinations. ing unnecessary examinations (skull films) is There are many reasons why it is undesir- potentially harmful. There are no findings on a able to have unnecessary radiologic examina- plain skull series to indicate (or not indicate) tions: excess cost, excess radiation, waste of the subdural or epidural hematoma (Figure 1-1). patient’s time, waste of the technician’s and Fewer than 10% of patients with fractures have radiologist’s time, and false hopes and expecta- subdural or epidural hematomas, and up to 60% tions based on the outcome of the examination. of patients with subdural or epidural bleeding In addition, and not least of all, they indicate a have no fractures.4 Therefore, why order the breakdown in the logical thought pattern con- examinations? Medicolegal reasons? On the cerning the patient’s workup. contrary! It is well documented that delays in Many examinations are ordered because of diagnosis in this setting can be fatal, so ordering so-called medicolegal considerations. It is be- unnecessary examinations might in fact be ask- lieved that if a certain finding (e.g., a broken rib) ing for a lawsuit. The American College of Ra- is not documented, the physician could be sued. diology has published appropriateness criteria In fact, few, if any, examples of medicolegal for when to order particular examinations and “covering yourself” types of examinations are has endorsed CT scans of the head as the initial valid. With the move toward greater consumer study of choice in trauma.5 awareness, lawsuits in the future are more likely Despite much documentation in the radiology to result from unnecessary radiation exposure and emergency department literature that show because of needless examinations rather than skull films’ lack of utility in trauma, they still are from too few examinations. commonly routinely ordered in many emergency departments throughout North America. A sur- vey performed in 1991 by Hackney and published EXAMPLES OF UNNECESSARY in Radiology6 reported that more than 50% of the EXAMINATIONS hospitals in the study “often or always” obtained skull films for trauma. Every hospital had CT Skull Series available. What are they thinking? Obviously they are not thinking about what a skull film will Except for a depressed skull fracture or the pres- show them that might affect their treatment, be- ence of intracranial metallic fragments, there is cause it won’t change a thing whether it is positive no reason to order a skull series for trauma. This or negative. was once one of the most abused examinations in radiology, costing millions of dollars per year Sinus Series unnecessarily. Although the number of unneces- sary skull films has decreased, they remain a It is true that an opaque sinus or an air-fluid level costly burden in many emergency departments. can be seen in a sinus series when sinusitis is Copyright © 2014 Elsevier, Inc. All rights reserved. 1 2 1  Unnecessary Examinations FIGURE 1-1 ​n Skull fracture. A thin radiolucent line char- FIGURE 1-2 n  Waters’ view of the sinuses. This film is acteristic of a skull fracture is noted (arrow) extending obtained with the patient’s head tilted slightly up- obliquely across the temporal bone. A fracture in this ward (as if he or she were drinking water—apologies area is often associated with an epidural hematoma to Dr. Waters). It is an excellent film to obtain when because the middle meningeal artery lies here. This the maxillary sinuses need to be seen. When done finding by itself, however, has little or no significance in an upright position, air-fluid levels can be seen and must be correlated with clinical findings. (arrow). present. However, the patient with these find- CT scan to search for additional fractures might ings is often asymptomatic, and just as often, the be in order, but not a nasal series. sinus series is interpreted as normal in another patient who has typical clinical findings of sinus- Rib Series itis. Both of these patients are treated based on their clinical, not radiographic, presentation, Fractured ribs are commonly seen in any radio- which is appropriate. Therefore the information logic practice. The significance of the finding from the sinus series is ignored. If that is the of a fractured rib or ribs is not well appreciated way you practice—and many recommend that as by most physicians. If the truth be known, the being proper—don’t order the sinus series: treat finding of a rib fracture after trauma has almost the patient. Reserve the sinus series for the no clinical significance and does not alter treat- patient who doesn’t respond to treatment or has ment. One must rule out a pneumothorax and an unusual presentation. Also, if it is only sinus- even a lung contusion, both of which are uncom- itis you are concerned with, most times a simple mon and are best done on chest films, not a rib upright Waters’ view (Figure 1-2) to examine series. In older patients with chest wall pain the maxillary and frontal sinuses, rather than a and rib fractures from undetermined causes, it full sinus series, will suffice, saving money and is extremely difficult and often impossible to dif- decreasing the patient’s exposure to radiation.7 ferentiate a pathologic rib fracture through a metastatic focus from a posttraumatic rib frac- Nasal Bone ture. Hence, obtaining x-ray films in a patient with focal rib pain to find a fracture serves little A nasal series is often requested to see if a patient purpose other than to find a cause for the pain. has suffered a broken nose after trauma to the Most rib series can be eliminated without chang- face. What if the nasal bone is fractured? It ing the way the patient is treated. won’t be casted. It won’t be reduced. In other words, no treatment will be given regardless of Coccyx what the x-ray shows. Therefore don’t order the films in the first place. Occasionally a nasal bone Although not a common x-ray examination, we is badly enough displaced to warrant interven- have occasional requests to x-ray the coccyx tion, but even then an acute, posttraumatic x-ray to rule out a fracture. As with the nasal bone study adds nothing for the patient except ex- and ribs, a fracture in this location will not be pense and radiation exposure. A facial series or a casted or reduced. Also, this examination has Copyright © 2014 Elsevier, Inc. All rights reserved. 1  Unnecessary Examinations 3 significantly more gonadal radiation dose than renal osteodystrophy to look for Looser’s frac- a rib or nasal series. Because no treatment is tures, brown tumors, and subperiosteal bone predicated on the x-ray results, don’t order the resorption. Most institutions have replaced the x-ray study for routine trauma to the coccyx. bone survey with hand films, which is preferable in regard to patient expense and radiation dose. Lumbar Spine Subperiosteal bone resorption is seen earliest and easiest on the middle phalanges, radial sides Plain films of the lumbar spine are probably the (Figure 1-3), and is virtually pathognomonic for most abused examinations in radiology. They hyperparathyroidism. Looser’s fractures are rare give the highest gonadal radiation dose of any and not treated. Brown tumors are uncommon plain film examination, and in most cases they and also are not treated. Therefore, if no treat- offer no diagnostic information that will be acted ment is based on the x-ray findings, the survey on by the physician. A significant number of only satisfies curiosity and is not worth the pa- lumbar spine films are done in persons younger tient’s money or radiation exposure. than age 40 who have acute onset of back pain after lifting or straining. There is virtually no Metastatic Bone Survey plain film x-ray finding in this patient subgroup that can be responsible for the acute problem or Little useful information is obtained from the that can be treated with intervention. Even the majority of metastatic bone surveys. Occult le- severest spondylolisthesis cannot unequivocally sions that are not found on radionuclide bone be said to be the origin of the symptoms. Disc scans are seldom encountered. Radionuclide herniation cannot be identified. Tumors and in- scans are more effective at picking up most fections are not clinical considerations in this metastatic lesions and could be substituted for setting. Treatment invariably consists of rest, bone surveys with less cost and better diagnostic nonsteroidal antiinflammatory drugs (NSAIDs), yield.11 Many investigators believe that search- overall relaxation of the muscle groups, and then ing for bone metastases is not warranted in every flexion and extension exercises to strengthen the patient with a primary tumor unless finding muscles. Radiographs have nothing to offer un- metastatic disease (mets) will obviate surgery or less the pain is very atypical or the clinical picture otherwise change the patient’s therapy. Radionu- is clouded by other considerations (e.g., intrave- clide bone scans with x-rays of questionable or nous drug use, in which case infection must be clinically suspicious areas makes more sense than ruled out). a complete metastatic bone survey. An exception The gonadal radiation dose from a lumbar spine film is the same as that from a daily chest x-ray for 6,8 16,9 or 98 years,10 depending on which study you choose to believe. These studies were based on a three-view lumbosacral spine series and do not include the oblique views rou- tinely obtained in many practices. Subtle osseous changes found on oblique views are thought by many orthopedists to be insignificant in most cases anyway. When should a lumbosacral spine series be ordered? In cases of severe trauma, possible pri- mary or metastatic tumor, and possible infec- tion. Acute low back pain with radicular signs is no indication for a spine series. An MRI scan will show disc herniation and would be the pre- ferred examination over plain films if clinically warranted. Generally a lumbar spine MRI ex- amination is performed only after a failed course of conservative therapy if disc disease is clinically suspected. Metabolic Bone Survey FIGURE 1-3 ​n Phalanges with subperiosteal bone resorp- tion. Subperiosteal bone resorption is seen as a subtle irregularity or interruption of the cortex. It is best seen Many institutions routinely order metabolic bone on the radial aspect of the middle phalanges (arrows) surveys in patients with hyperparathyroidism or and is pathognomonic for hyperparathyroidism. Copyright © 2014 Elsevier, Inc. All rights reserved. 4 1  Unnecessary Examinations to this is in patients with multiple myeloma. Radionuclide bone scans are often negative in multiple myeloma, even with marked skeletal involvement; hence a plain film bone survey is warranted in these patients. Ankle Series The most common cause for presentation to emergency departments in North America is an ankle sprain, with more than 30,000 ankle sprains reported each day.12 Ligamentous injuries can easily be clinically differentiated from significant fractures. One study reported that a 50% reduc- tion of ankle films resulted in no fractures being missed when the radiology resident simply exam- ined the patients.13 Another study revealed that if the patient were able to walk three steps immedi- ately after the injury or during the examination in the emergency room there was almost zero chance of a fracture.14 This study was one of sev- eral to use what has been called the Ottawa ankle rules for when to obtain ankle x-ray films. They are so named after the hometown of the first authors to implement them and are in wide- FIGURE 1-4 n  Ankle after trauma. Calcific densities spread use today in most emergency departments around the ankle that can be mistaken for avulsions are often seen (arrow). When rounded and smoothly in North America. Small bony avulsions receive corticated, as in this example, they are either acces- the same treatment as ligament tears and are sory ossicles or old avulsions. An acute avulsion is often difficult to differentiate from accessory best diagnosed clinically by noting point tenderness ossicles (Figure 1-4). Therefore in most cases the at ligament insertion sites. Because a ligament can x-ray film is not a factor in determining the avulse with or without a fragment of bone being attached, the x-ray finding will not influence the patient’s treatment and should be skipped. patient’s treatment. Lumbar Myelograms One of the most painful radiologic examina- (Figure 1-6). We can hope that the myelogram tions extant is the lumbar myelogram, in which will go the way of the pneumoencephalogram a spinal needle is placed into the subarachnoid and the epidural venogram. space of the lumbar spine and contrast material So far as choosing between a CT and an MRI is injected (Figure 1-5). Although this is done scan of the lumbar spine for disc disease and spi- for tumors, it is most commonly performed in nal stenosis, an MRI examination will give much the workup of lumbar disc disease. Many studies more diagnostic information and is considered show that a CT or MRI scan of the lumbar the state-of-the-art imaging examination for the spine is more accurate than myelography in di- spine, although, as the next section shows, an agnosing disc disease and emphasize that a CT MRI scan of the lumbar spine is one of the most or MRI scan should be the study of choice. overused imaging tests in the country. Many surgeons, however, still request myelo- grams in addition to the CT or MRI study when MRI Lumbar Spine only the CT or MRI need be performed. In ad- dition to being painful, the myelogram pro- Much has been written in the lay press in the duces side effects in some people that can be past few years concerning the overuse of medical pronounced and debilitating; the myelogram testing at a time when our economy is reeling occasionally necessitates overnight hospitaliza- from skyrocketing medical costs. One of the tion; the radiation dose from the myelogram is imaging tests mentioned near the top of every higher overall than with CT; and perhaps most list is an MRI study of the lumbar spine. Multi- important, the myelogram is not as accurate and ple studies have shown that as many as one third does not give as complete a picture of additional of asymptomatic individuals older than age 50 back structures as the CT or MRI examination will have one or more focal disc protrusions.15 Copyright © 2014 Elsevier, Inc. All rights reserved. 1  Unnecessary Examinations 5 FIGURE 1-6 n  Lumbar MRI. Axial T1-weighted (top) and T2-weighted (bottom) images through the L4-5 FIGURE 1-5 n  Lumbar myelogram. An iodinated con- disc space show a focal lateral disc protrusion trast material has been injected into the subarachnoid (arrows) encroaching on the left neuroforamen. This space by way of a spinal needle. A large extradural type of disc protrusion would likely not be seen on defect is seen that is caused by a disc protrusion. A a myelogram. tumor could have a similar appearance. This examina- tion can be quite painful, has occasional long-lasting complications, and gives no information that could not be obtained with an MRI examination. In some Cervical Spine (C-Spine) institutions it requires an overnight stay in the hospi- tal as well. For these reasons the standard of practice Many emergency departments routinely order today is an MRI scan. C-spine films for all trauma patients, primarily because of the horrible consequences of not stabi- lizing a fractured neck. This is ridiculous. It has been demonstrated in numerous publications that Often the patient’s pain and examination coinci- patients who are alert and have no C-spine pain dentally correspond to the location of the disc have almost zero chance of having a fracture.16 If protrusion, resulting in unnecessary surgery. the patient is unconscious, is obtunded for what- More times than not, the MRI scan shows ab- ever reason, is unable to communicate, or has normalities that have no clinical correlation a significant fracture elsewhere, all bets are off. whatsoever, resulting in diagnostic confusion. In However, if the patient is alert and has no pain most cases an MRI scan of the lumbar spine with motion on clinical examination of the neck, should not be performed unless 6 to 8 weeks of no posterior midline tenderness, and no neuro- conservative care has been afforded, and even logic deficits, no C-spine film need be obtained.17 then, if surgery is not being considered, why pay As for plain films of the C-spine in trauma, for an expensive imaging study? Certainly an a case should be made for skipping a plain film MRI study would be reasonable if the clinical C-spine series and going straight to a CT presentation were atypical or if trauma, tumor, scan. The obvious reason for this is that a or infection were clinically suspected. Several negative plain film will not exclude a fracture; studies have reported that surgeons and other therefore a CT scan will be performed regard- medical specialists who own their own MRI less of what the plain film shows (a CT scan is units order many more examinations than when always obtained when a fracture is found). the MRI unit is not self-owned. Lumbar spine One caveat is that if the CT scan shows no MRI studies tend to be the most overused ex- fracture, the patient could still have ligamen- amination I see daily. tous disruption, which would not be seen on a Copyright © 2014 Elsevier, Inc. All rights reserved. 6 1  Unnecessary Examinations CT scan unless there is malalignment. A diag- 3. Seelig JM, Becker DP, Miller JD, et al: Traumatic acute nosis of ligamentous disruption requires that a subdural hematoma. N Engl J Med 304:1511–1518, 1981. flexion-extension plain film or an MRI scan be 4. Masters JS, McClean PM, Arcarese JS, et al: Skull x-ray done. Some say obtaining a CT scan on every examinations after head trauma. N Engl J Med 316:84–91, patient in whom only a plain film is currently 1987. obtained would inundate most scanners with 5. American College of Radiology: ACR Appropriateness Criteria Head Trauma, 2001. Available at http: //www. unnecessary examinations, because the major- acr.org. ity of plain films of the C-spine aren’t really 6. Hackney DB: Skull radiography in the evaluation of needed. Hello! If they aren’t really needed acute head trauma: a survey of current practice. Radiology then don’t get them! 181:711–714, 1991. 7. Williams JJ, Roberts L, Distell B, Simel D: Diagnosing sinusitis by x-ray: comparing a single Waters view to 4-view paranasal sinus radiographs. J Gen Intern Med TECHNICAL CONSIDERATIONS 7:481–485, 1992. 8. Webster EW, Merrill OE: Radiation hazards: II. Mea- Avoiding unnecessary examinations constitutes surements of gonadal dose in radiologic examinations. N Engl J Med 257:811– 819, 1957. only one way to decrease unnecessary radiation 9. Antoku S, Russell WJ: Dose to the active bone marrow, exposure in the general population. Another way gonads, and skin from roentgenography and fluoroscopy. to significantly diminish exposure is to collimate Radiology 101:669–678, 1957. the x-ray beam tighter. One study reported that 10. Andron GM, Crooks HE: Gonad radiation dose from if collimation were limited just to the size of the diagnostic procedures. Br J Radiol 1957;30:295–297. 11. Mall JC, Bekerman C, Hoffer PB, et al: A unified radio- film, radiation dose could be reduced by one logical approach to the detection of skeletal metastases. third.18 Exposure could be further reduced by Radiology 118:323–329, 1976. having proper filtration, fast screen-film combi- 12. Cheung Y, Rosenberg ZS: MR imaging of ligamentous nation, and adequate gonadal shielding. Digital abnormalities of the ankle and foot. Magn Reson Imag- ing Clin N Am 9:507–531, 2001. radiography, which is gaining widespread use, 13. Auletta A, Conway W, Hayes C, et al: Indications for will further help decrease radiation dose. Cer- radiography in patients with acute ankle injuries: role of tainly having properly trained technicians and the physical examination. Am J Roentgenol 157:789–791, properly functioning equipment will diminish 1991. the number of retakes. These should be high- 14. Stiell I, Greenberg G, McKnight R, et al: Decision rules for the use of radiography in acute ankle injuries. JAMA priority goals for all radiologists to make our 269:1127–1132, 1993. specialty more cost-effective and to provide bet- 15. Jarvik JJ, Hollingworth W, Hoagerty P, et al: The longi- ter service to both the referring clinician and the tudinal assessment of imaging and disability of the back patient. It should be part of every radiologist’s (LAIDBACK) study: baseline data. Spine 26:1158–1166, 2001. responsibility to help educate and guide the un- 16. Mirvis S, Diaconis J, Chirico P, et al: Protocol-driven knowing clinician in obtaining the appropriate radiologic evaluation of suspected cervical spine injury: imaging examinations while eliminating those efficacy study. Radiology 170:831–834, 1989. that are unnecessary. 17. Hoffman JR, Mower WR, Wolfson AB, et al: Validity of a set of clinical criteria to rule out injury to the cervical REFERENCES spine in patients with blunt trauma. N Engl J Med 343: 94–99, 2000. 1. Hall F: Overutilization of radiological examinations. 18. Morgan RH: Hearings before the Committee on Com- Radiology 120:443–448, 1976. merce, Science and Transportation. U.S. Senate, an 2. Abrams HL: The “overutilization” of x-rays: sounding oversight of radiation health and safety. 95th Congress, board. N Engl J Med 300:1213–1216, 1979. 1st session, June 1977, pp. 241–266. Copyright © 2014 Elsevier, Inc. All rights reserved. C H A P T E R 2 Benign Lytic Lesions A benign, bubbly lytic lesion of bone is probably entities that cause benign lytic lesions is quite one of the most common skeletal findings a radi- long; therefore a mnemonic is helpful in recall- ologist encounters. The differential diagnosis can ing them. be quite lengthy and is usually given on an “Aunt I was a flight surgeon in the Air Force before Minnie” basis (I know that’s Aunt Minnie be- my radiology residency, and I would spend a half- cause she looks like Aunt Minnie); in other day every week or so with the radiologist, trying words, the differential diagnosis is structured on to pick up some pearls. This radiologist was Ivan how the lesion looks to the radiologist based on Barrett, and he did me a great favor: he taught his or her experience. This method, called pat- me the mnemonic FEGNOMASHIC, which is tern identification, certainly has merit, but it can made up from the first letter of each of the enti- lead to many erroneous conclusions if not tem- ties in the differential of benign lytic lesions of pered with some logic. For instance, most radi- bone. For instance, the F stands for fibrous dys- ologists would justifiably miss the diagnosis of a plasia; the E, for enchondroma; and so on. I dili- rare presentation of a primary malignant neo- gently learned what each letter stood for, even plasm that initially looks benign. Many of these though I had no idea what most of the processes radiologists would subsequently insist on includ- were or looked like on an x-ray film. Before I ing primary malignant neoplasms in their benign could learn another mnemonic from Ivan (I was lytic differential even though the rare malignancy a slow learner), I moved away to begin residency. is “1 in a million.” If every differential is geared Sure enough, the first week of residency, in a to cover even the long shots, there would be a lot formal conference with 15 to 20 residents pres- of extremely long differentials and the clinicians ent, I was chosen as the sacrificial lamb among wouldn’t get much useful information from us. the first-year residents to take an unknown case. We might as well give the clinician the index to a It happened to be a benign lytic lesion, which multivolume bone book as the differential to I proceeded to expound on with a list of 12 to ensure we never miss anything. 15 differential possibilities. The conference room Then again, you don’t want a differential di- got quiet, I was thanked cordially but a little agnosis list that is wrong half the time. You could frostily, and the conference was adjourned. One almost do better with a coin flip. I’m willing to of the first-year residents whom I barely knew at accept a differential that is accurate (i.e., one that the time asked how I knew so many of the pos- contains the correct diagnosis) 95% of the time. sibilities on that case, because the staff man This is acceptable to me for most skeletal enti- showing the case (who was a chest radiologist) ties; however, I would be remiss if I were willing didn’t even know that many. I explained, with a to accept a 1-out-of-20 miss rate for fractures straight face, that those simply seemed like the and dislocations. Nevertheless, for most of the logical things to mention. I was trying to be entities in this book I will accept 95% accuracy matter-of-fact and not come off as too much of in differentials and would expect most radiolo- a show-off, but I couldn’t help laughing. I then gists to concur. If you want to be more accurate told the resident how I had learned a single mne- than that, you simply add more diagnoses to the monic and how with a little luck it made it seem list of differential possibilities. like I knew a lot more than I really did. He and The shorter the differential diagnosis list is, the rest of my fellow residents were relieved that the handier it is to remember and apply. As the I really wasn’t any smarter or more advanced differential list gets longer, it generally gets than them and quickly learned the mnemonic more accurate but it can be difficult to remem- themselves. I became hopelessly addicted to ber and often falls into disuse. Mnemonics are mnemonics from that day on. helpful in recalling long lists of information, and I will pass on many that I use; many people, however, do not like to use mnemonics (for no FEGNOMASHIC good reason that I’ve been able to ascertain) and will have to use whatever method works for FEGNOMASHIC is defined in Funk and Wagner’s them to remember the differentials. The list of unabridged dictionary, 13th edition, as “one who Copyright © 2014 Elsevier, Inc. All rights reserved. 7