Oral Health Group

A Sherlockian Approach to Radiographic Interpretation

December 1, 2014
by Mitra Sadrameli, DMD, MS


Dental clinicians perform few procedures without acquiring diagnostic radiographs. Much of the structures of the teeth and the oral cavity are hidden from the treating dentist, and diagnostic radiographs aid in revealing hidden etiologies. Interpretation of the radiographs brings about fears of missing lesional characteristics. The most prevalent error is not missing the lesion but over diagnosing pathology when there is none. The inherent subjectivity of radiographic interpretation, contributes to the clinician’s decrease or lack in confidence.1

There are great similarities between the radiographic appearances of many jaw lesions often resulting in difficulties in differentiating between them. Radiographic evaluation of jaw lesional characteristics, such as location, margin, density, relation to tooth/teeth, as well as clinical presentation, generally help in narrowing the differential diagnosis.2,3 Understanding the hidden clues within various radiographic appearances helps alleviate or give urgency to follow-ups, referrals, and treatment options.

This paper is a review of characteristics of common lesions or findings presented in two-dimensional (2D) radiographs with a focus on differential diagnosis, in order to formulate appropriate management.

Many lesions with very different treatments or prognoses share similar clinical, radiographic or histologic characteristics. The information within the radiograph is complex and dependent on the imaging modality, its degree of technique sensitivity, image processing procedures and patient’s anatomy.4 As Kantor et al suggested, the first three of these parameters should be controlled and optimized to ensure optimization for the best radiographic image obtainable, with the least radiation dose given to the patient.4 The last item on their list, patient’s anatomy, must be understood in a comprehensive manner.

Radiology is more a science and less an art. And as in all fields of science, its principles must be learned and practiced. While radiographs are immensely important, patient medical history, examination, laboratory results, histopathologic analysis and surgical findings must be taken into account to form the final diagnosis. However, correct interpretation of the radiographic features may suggest a more accurate differential diagnosis, aiding in improved presurgical planning and patient care by preventing or prompting treatment.

FIGURE 1. A well-defined peripheral radiopaque area surrounding a periapical radiolucency associated with inflammatory pulpal infection (rarefying osteitis) is suggestive of an extremely slow-growing self-contained, nonaggressive, benign osteolytic lesion enlarging by expansion, such as a radicular cyst, granuloma, or abscess. Also note sclerosis of the surrounding bone, result of host response to an inflammatory process such as infection.

FIGURE 2. An ill-defined radiolucent lesion associated with the mesial and distal roots of teeth #3.6 and 3.7 as well as sclerosis of the surrounding bone is evident. Note destruction of the lamina dura within the radiolucent lesion.

FIGURE 3. Tooth # 2.5 exhibits symmetrical widening of the PDL space.

The decision of when to refer, and to which specialist, can only be made when a proper working diagnosis of the lesion is made. Successful management of a patient is heavily dependent on accurate interpretations of the signs and symptoms, without which the response to treatment is at best unpredictable, and at worst ineffective. It is a Sherlock Holmes business, where the most subtle of clues may make the difference between speedy recovery or prolongation of the patient’s chief complaint. Deciphering the clues requires clear thinking, attention to gross, as well as minute details and abundance of curiosity.

A systematic approach in analysis of the images at hand is another requisite. Regardless of the type of radiograph, especially when reviewing complicated images, adhering to a systematic approach prevents missing important but subtle findings.

The jaws, while similar to some other skeletal bones, are uniquely different. Embryologically, they are for the most part derived from migrating cells of the cranial neural crest (ectomesenchyme), as well as mesodermal cells, a combination found in other skeletal bones. However, most importantly, they contain teeth, a structure not found in other skeletal bones.5 Presence of teeth results in formation of cysts and tumors of odontogenic origin not encountered in other skeletal hard tissue.

In general terms, lesions may be divided into radiolucent, radiopaque or mixed. While this is a good starting point, given that many lesions may progress through all three stages with the initial presentation of homogenous radiolucent to mixed to radiopaque, the diagnostic value becomes limited. However, as with all classifications, a flawed system is better than none. Even a flawed classification aids in an initial organization of thought. One must not allow, however, an initial assumption to supersede all other signs and clues presented radiographically, histologically or clinically.

For the dental professional, every clinical and radiographic encounter results in an initial impression, which in essence is a subjective probability of disease.6 As the initial impression is refined and modified, a working diagnosis is reached, which in the majority of cases is the declaration of the most probable disease or series of diseases that adheres to the signs and symptoms presented by the patient. Diagnostic tests are therefore used to modify or refine initial impressions, confirm or rule out differential diagnoses between diseases with similar overall characteristics. The initial impression is reached based on a subjective impression, be it clinical or otherwise. When applicable, utilizing objective tests, such as laboratory or radiographic exams, allows greater scientific weight to be given to existing or new impressions.

Therefore, each diagnostic test ordered must answer specific question(s) pertaining to the patient’s specific condition. Imaging modalities selected may or may not provide all the required answers; as such a thorough understanding of the limitations of the images ordered is as important as understanding their benefits.

FIGURE 4. Resorption of mesial root #3.6

FIGURE 5. Sclerosing osteitis presenting as a well-defined radiopacity centered on the distal root #4.7 with a large carious lesion. Image courtesy of Dr. Aditya Tadinada & Dr. Sonya Kalim

FIGURE 6. Well-defined, homogeneous radiopaque finding in the edentulous site of #4.7, suggestive of idiopathic osteosclerosis. Image courtesy of Dr. Aditya Tadinada & Dr. Sonya Kalim

FIGURE 7. Periodontally involved tooth #3.7 presenting with floating in air appearance.

The working diagnosis is an attempt to offer an explanation that takes into consideration information from various sources. According to Langlais et al2 these include:

1. Chief complaint and its history if applicable

2. Demographic information with respect to age, sex and race

3. Social, medical and dental history

4. Radiographic findings

5. Laboratory values if needed

6. Additional examinations, tests or consultations if needed

Radiographs are commonly used in dentistry to evaluate maxillofacial or oral anatomic sites. Successful interpretation or analysis of radiographs requires optimum quality images. These images must be free of distortions (foreshortening or elongation), and have proper contrast unencumbered by exposure or developing errors.7 Details hinting to a final diagnosis of osteoporosis may disappear in overexposed or underexposed images, rendering correct diagnosis difficult if not impossible.

Radiographic evaluation requires a systematic approach. In the same type of radiograph, the exact same areas are evaluated in the same order each and every time. By establishing a pattern, while initially ignoring the lesion in question (in order to rule out pathologies and abnormalities in other areas of the radiograph), the image is carefully reviewed. Once satisfied, attention can then be turned to the area(s) of concern.

When it comes to radiographic analysis one view is no view. An obvious example is the superimposition of the radiolucent mental foramen on the apex or apices of the mandibular premolars mimicking an inflammatory periapical lesion. A second radiograph acquired with a slightly different angle will confirm or rule out the working diagnosis. If the radiolucent area moves away from its location on the first radiograph as it appears, the finding is consistent with superimposition of the mental foramen on dental structures. In addition, vitality test of the tooth/teeth should yield a positive response.

The approach to the areas of concern remains similar for both the radiologist and the non-radiologist colleagues. When faced with a maxillofacial lesion of unknown diagnosis, many radiology residents are taught to start with a detailed description of the lesion.

Since some radiographic findings are not always lesional, I will use the word “finding” as a general term to encompass both pathological and incidental non-pathological findings. The word “lesion” will be reserved for pathological entities. Based on radiographic appearance, lesions and findings are divided into osteoblastic (radiopaque), osteolytic (radiolucent), and radiopaque/radiolucent (mixed).

Bone tissue is continuously formed and remodeled throughout one’s life.8 Bone formation is a tightly controlled mechanism which balances deposition (osteogenesis) and resorption (osteolysis) activities.8 Interruption of this balance results in osteoblastic or osteolytic findings. Endocrine dysfunctions, hormonal imbalances, genetic malfunctions or mutations, may contribute or cause osteoblastic or osteolytic instability, creating areas of altered radiographic appearance.

The following will help in narrowing the range of differential diagnoses in lesions with similar imaging characteristics:

1) Location of the lesion
While there are exceptions, some findings have strong preferences for specific locations in the jaws. For example, the majority of keratocystic odontogenic tumors (aka KOT) are present in the mandibular molar region.2,9 Odontogenic lesions occur in the environment where teeth are present, hence they are seen superior to but almost never in the areas inferior to the mandibular canal. Non-odontogenic lesions do not respect this distinction.2,3 Another radiographic sign, the direction of the mandibular canal displacement, may offer clues to the nature of the lesion. A downward displacement of the canal may be caused by an odontogenic lesion, however, a superiorly displaced canal will not have an odontogenic etiology.2 Ground glass appearance of the mandibular body and superior displacement of the mandibular canal suggests a non-odontogenic lesion, such as fibrous dyplasia.

2) Internal density of the lesion
Relative to the density of the adjacent bone, the lesion may exhibit a radiopaque, radiolucent or mixed appearance.2,3

3) General description of the lesion:

a. Margins.2,3,10

i Presence or absence of corticated margins.

ii Ill or well-defined margins – In general, a lesion with a well-defined (circumscribed) margin is suggestive of a self-contained lesion enlarging by expansion and is predominantly benign. A lesion with an ill-defined (diffuse) border is suggestive of a lesion enlarging by invading the surrounding bone, such as in aggressive inflammatory or neoplastic pathology.

iii Intact or perforated margins.

b. Presence of internal loculations2,3

i A multilocular radiolucent pattern (also referred to as honeycomb, soap-bubble, tennis racket or scalloped pattern) suggests a locally aggressive benign tumor, such as an ameloblastoma, or odontogenic myxoma.

ii Well-defined, unilocular radiolucent lesions usually indicate a slow growing benign process. Multiloclular lesions with well-defined margins suggest a benign but aggressive lesion.

4) Patterns of lytic changes
Categorizations such as geographic, permeative and motheaten lytic patterns, allow a degree of tumoral behavior prediction.2

a. Geographic lytic pattern suggest either an aggressive benign or a low-grade malignant lesion.

b. Moth eaten lytic pattern signals either an inflammatory condition, such as chronic osteomyelitis or a primary or metastatic malignant lesion.

c. Permeative lytic pattern indicates aggressive rapidly destructive malignant lesion.2

5) Pattern of the host bone’s defensive reaction to the lesion2,3,5,9,10,11

a. Presence of periosteal new bone formation is most commonly indicative of host bone reaction to chronic inflammatory processes such as osteomyelitis. There are also specific periosteal reactions seen
mostly with malignant lesions, such as the sunburst type periosonteal reaction associated with osteosarcoma or laminated (onion skin) periosteal reaction associated with Ewing sarcoma.

b. A well-defined peripheral radiopaque area surrounding a periapical radiolucency associated with inflammatory pulpal infection (rarefying osteitis) is suggestive of an extremely slow-growing self-contained, nonaggressive, benign osteolytic lesion enlarging by expansion, such as a radicular cyst, granuloma, or abscess (Fig. 1). The bone surrounding the lesion becomes dense in order to prevent spread of the lesion.

c. Significant inflammatory disease may result in formation of an ill-defined radiolucency, destruction of the lamina dura and the alveolar bone surrounding the root(s) (Fig. 2).

6) Changes in the periodontal ligament (PDL) space and lamina dura dimensions2,8-10

a. Careful evaluation of the teeth and the size of the lamina dura may reveal symmetric widening of the PDL space of one or more teeth, suggestive of occlusal trauma (Fig. 3), infection, osteomyelitis or malignant lesions such as early phases of osteosarcoma, or leukemia. In a young person, they are also associated with terminal stages of root formation.

b. Asymmetric widening of the PDL space may be associated with trauma from torqueing forces, orthodontic movement, or malignancies.

c. Circumferential widening of the PDL space on many or the full complement of teeth should prompt consideration of active orthodontic treatment as well as diseases such as progressive systemic sclerosis (scleroderma), osteomyelitis, bisphosphonate related osteonecrosis, or leukemia.

7) Effect of the lesion on the surrounding structures.2,3,7,9,10,11,12,13

a. In deciphering the clues, it is important to determine the effect of the lesion on the surrounding structures. Displacement of teeth is a common finding in slow-growing, space-occupying lesions. Lesions starting in the ramus may push teeth in the anterior direction. Notwithstanding a few exceptions, resorption of the teeth occurs in chronic and slow-growing processes. Apical inflammation & root resorption have been reported with necrotic and pulpal infection (Fig. 4), as well as with slow growing tumors such as cysts, giant cell tumors, osteosclerosis and fibro-osseous lesions.14 While rapidly growing tumors are more destructive to the bone rather than the roots.2,14

b. Slow-growing lesions with tendencies to increase in size often cause expansion with cortical bowing. Rapid cortical destruction is considered an aggressive inflammatory or malignant characteristic. However, some non-neoplastic conditions such as an aneurysmal bone cyst (ABC) also exhibit rapid growth. ABC usually presents with well-defined albeit ballooned cortical margins which differentiates it from malignant lesions with ill-defined margins, although reports of uncommon destruction of the cortical bone associated with ABC has been published.

c. Malignant lesions on the other hand may exhibit rapid growth within the periodontal ligament (PDL) space, causing irregular widening and destruction of the lamina dura. Widening of the mandibular canal in the presence of intact corticated canal walls, may indicate presence of a benign neurovascular lesion.

8) Progression of the findings
If osseous changes are not evident, the lesion is static.

Most radiopaque findings are asymptomatic and are incidental findings. As a result, many of the most commonly encountered radiopaque findings do not require immediate intervention. Some are observed over a long period of time with no perceptible change.11 The majority present as well-defined findings suggesting a benign or inflammatory origin.3

Radioapaque lesions can be divided into two main groups: focal and generalized. Focal lesions are divided further, based on anatomic site, into periapical, and non-periapical.

Sclerosing osteitis

is considered a periapical lesion. Sclerotic bone in the jaws can be caused by trauma, stress, or infection.15 Also known as condensing osteitis, this lesion is associated with current or prior pulpal inflammation.5 These are usually centered at the apices of the root(s) housing the inflamed pulp or may be seen in the anatomic sites of previously extracted teeth, presenting as well-defined radiopacities (Fig. 5). A negative vitality test of the tooth is confirmation of this diagnosis. This is the feature which differentiates sclerosing osteitis from the following findings or lesions.

A periapical or non-periapical well-defined, fairly homogeneous radiopaque finding coupled with an absence of radiolucent peripheral rim, and no history of inflamed associated tooth, is suggestive of idiopathic osteosclerosis (Fig. 6), and is considered a variation of normal bone development. They present as regular or irregularly shaped findings of varying sizes.5 As the name implies, etiology of idiopathic osteosclerosis also remains unknown. Since these are non-inflammatory related findings, the involved teeth are vital.5

Depending on the shape, location and size, other differential diagnoses for idiopathic osteosclerosis may include complex odontoma. Both present as fairly homogeneous radiopaque regions, with regular or irregular shape and of varying sizes. Complex odontoma however, is surrounded by a radiolucent rim, whereas idiopathic osteosclerosis is not. As we have seen, diffused sclerotic bone may also be the end result of host bone reaction to a mild, chronic, mechanical or chemical irritation, so the location and association with existing or history of previous odontogenic diseases such as caries will aid in diagnostic evaluation, and differentiate this finding from sclerosing osteitis.5 Based on radiographic appearance only, other differential diagnosis may include mature fibro-osseous lesions (e.g. periapical cemento-osseous dysplasia) and sclerosis of surrounding bone due to external factors such heavy occlusal stress.11

Sclerosing osteitis and idiopathic osteosclerosis are non-expansile asymptomatic findings, where the covering mucosa is normal in appearance. Maxillary sinus involvement and regional lymphadenitis is not characteristic of these findings. Sclerosing osteitis may remain unchanged, partially resolve or completely disappear after successful treatment of infected teeth. While in most post-treatment cases these remain dormant with no perceptible changes, serial radiographs showing increase in size indicate an active lesion.5

While less common, the osteosclerosing tumors also present with internal opacities. They may present with irregular sclerosis resulting from a primary or secondary osseous malignancy and/or may be coupled with aggressive signs, such as local or generalized expansion. These lesions are outside the scope of this article.

There are three distinct types of generalized diminished bone density, osteoporosis, osteomalacia, and osteolysis.8 Each with its own unique etiology. Radiographically, diffuse bone loss without chemical abnormalities in the composition of the bone is associated with osteoporosis and generalized osteolysis.8 In comparison, osteomalacia, is marked by diminished mineralization of the osteoid, resulting in abnormal chemical composition, which results in greater elasticity of the bone.8 Osteolysis is generally considered to be a focal or regional loss of bone as a direct result of a pathologic process such as infection, neoplasm, or local manifestations of systemic diseases.

Local inflammation is frequently associated with poor osteolytic margins and periostitis.13 Interestingly, radiographic findings of a small number of malignant tumors may also present with similar findings.13 Differentiation between these vastly different processes with similar radiographic presentations may not yield an accurate final diagnosis of a tumor or tumo
r-like lesions but will provide reliable information regarding a tumor’s aggressiveness.13 Consideration of the patient’s age, gender and location of the lesion will aid in narrowing the differential diagnosis even further. Advanced cases of osteosarcomas, for example, present as poorly defined lesions with an internal appearance that may be radiolucent, radiopaque or mixed, depending on the longevity of the lesion. A characteristic of osteosarcoma is significant osteolysis around a tooth, creating the appearance of tooth floating in air. Other conditions such as periodontal disease, which is an inflammatory lesion, may also present with floating tooth/teeth appearance. Severe periodontal disease remains the most common cause of floating teeth (Fig. 7). The crestal bone loss in periodontal disease is most commonly generalized and not localized as usually presented by osteosarcomas.

Malignant tumors of the jaws mostly arise from metastatic primary lesions adjacent to the oral cavity or distant tumors.13 In order of frequency, the primary tumors metastasizing to the jawbones are carcinoma of the breast, kidney, lung, colon, prostate and the thyroid.13 Breast, thyroid and prostate metastases may present as mixed lesions.13 While prostate and thyroid metastatic tumors may present as purely radiopaque.13 In the maxillary sinuses, metastatic lesions can cause opacification and indistinct bony margin.13 Metastatic lesions to the jaws occasionally may be evident prior to the discovery of the primary tumoral site, highlighting the importance of early disease detection.13 These lesions generally affect patients in the fifth and sixth decade of life.13 The mandible is more commonly affected with greater predilection for the premolar-molar region.2,13 The clinical manifestations are varied with the patient’s chief complaint ranging from pain, loosening or extrusion of teeth to unexplained paresthesia.13 Radiographic signs are also varied, ranging from single or multiple, purely radiolucent, purely radiopaque or mixed lesions.13 However, aggressive radiographic signs distinguish between inflammatory and neoplastic lesions.

Most malignant lesions are radiolucent. They present with ill-defined borders/margins, are not encapsulated, and exhibit profound and rapid cortical bone destruction. Internal trabecular bone is destroyed. Some may invade other tissues or structures such as the maxillary sinuses. With the exception of osteosarcoma, and metastatic prostate cancer, no periosteal reaction is evident. Local host bone reaction is also absent.

Benign lesions on the other hand are well-defined, mostly slow-growing, lesion with visible, sclerotic borders. They may displace existing structures such as adjacent teeth, are expansile resulting in thinning of the cortical plates. Prevalence of periosteal new bone formation is greater with benign lesions.

In general lesions with expansion, cortical destruction should be further evaluated.

Mixed lesions offer a large range of possible etiologies including developmental, inflammatory, metabolic, fibro-osseous, or less commonly malignant lesions.2,3

Sclerosing osteomyelitis is a chronic osteomyelitis which presents with sclerosis of the sequestrum or the surrounding bone.5

Other periapical radioapacities may appear with various degrees of internal opacities. Periapical cemento-osseous dysplasia (PCD) presents with a thin, uniform radiolucent rim in the mature radiopaque stage.5 PCDs have a predilection for African-American and Asian middle aged women. Lesions are characteristically round with well-defined borders. A thin radiolucent halo separates the lesion from the root and the surrounding normal bone.5 Mature PCD may present as homogeneous apical opacities similar in appearance to sclerosing osteitis. The former will test positive to vitality test while the latter does not. Also, while the latter may be seen at the apex of any tooth, PCD is generally associated with the anterior mandibular teeth. Etiology of PCDs is unknown but is generally considered a reactive process, which requires no treatment unless they become symptomatic or infected.

Understanding the proper use of various imaging techniques, the meaning of important imaging signs and accurately interpreting them is essential in reaching a correct diagnosis. Radiology allows us to observe the internal anatomy and evaluate the otherwise hidden tissues. The ubiquity of various imaging techniques means that variations of normal and pathologic tissues (whether silent or symptomatic) may be easily discovered, provided that the images are reviewed carefully and the radiographic signs are interpreted accurately.

Pattern recognition is the first step to interpreting radiographic images. Following this, a thorough knowledge of clinical findings, pathology, pattern of disease behavior, as well as histological changes underlying the radiographic findings, will aid in reaching a final or a well-reasoned differential diagnosis.

When we exchange the habit of brief inspection, mixed with intuition, resulting in an instant diagnosis, for a more systematic and measured thought process, both the patient and the profession benefit equally. OH

Dr. Mitra Sadrameli received her DMD in 1992 from university of Florida. Following graduation, she completed the AEGD program at Columbia University College of Dental Medicine in New York City, and maintained a private practice in general dentistry until she returned to graduate school in 2009 to earn her certificate in Oral and Maxillofacial Radiology and Masters in Science at University of Texas Health Science Center in San Antonio, (UTHSCSA). She is a diplomate of the American Board of OralMaxillofaical Radiology (ABOMR). Author of a number of articles, she has delivered presentations nationally and internationally on 3D imaging, its influence on personal patient care including diagnosis of pathology, dental implant, surgical & prosthetic planning. She currently maintains a private practice in Oral maxillofacial radiology

Oral Health welcomes this original article.


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