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Year : 2012? |? Volume : 1? |? Issue : 2? |? Page : 95-104 |
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Zygomatic air cell defect
Srikanth H Srivathsa, Mahima V Guledgud, Karthikeya Patil
Department of Oral Medicine and Radiology, JSS Dental College and Hospital, JSS University, Mysore, India
| Date of Submission |
02-Oct-2012 |
| Date of Acceptance |
24-Nov-2012 |
| Date of Web Publication |
8-Jan-2013 |
Correspondence Address:
Srikanth H Srivathsa
Department of Oral Medicine and Radiology, JSS Dental College and Hospital, JSS University, Mysore - 570 015, Karnataka
India
DOI: 10.4103/2278-9588.105698
Zygomatic air cell defect is extension of pneumatization of temporal bones anteriorly into the articular tubercle. These are variations of normal structures which can be detected on the simplest imaging modality, the panoramic radiograph. A literature search, electronic as well as manual, was done using the keywords zygomatic air cell defect, pneumatized articular eminence and pneumatized articular tubercle. The search yielded considerable literature on the topic, which was analyzed thoroughly for its contents and this paper reviews this normal variant from the time of its recognition to the present day updates. It can be concluded that the zygomatic air cell defect has a low prevalence in general population and can be mistaken for a pathologic process. Further, if not recognized in subjects undergoing surgical procedures may lead to inadvertent complications such as leakage of cerebrospinal fluid.
Keywords:?Air cells, pneumatized articular eminence, pneumatized articular tubercle, zygomatic air cell defect
How to cite this article:
Srivathsa SH, Guledgud MV, Patil K. Zygomatic air cell defect. J Cranio Max Dis 2012;1:95-104 |
How to cite this URL:
Srivathsa SH, Guledgud MV, Patil K. Zygomatic air cell defect. J Cranio Max Dis [serial online] 2012 [cited?2013 Feb 20];1:95-104. Available from:?https://craniomaxillary.com/text.asp?2012/1/2/95/105698 |
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??Introduction |
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The temporal bones are pneumatic bones. Air cells are a series of communicating cavities present within bone which are lined by mucous membranes. [1] Pneumatization is seen in majority in the para-nasal sinuses. The pneumatized air cells present in the zygomatic process of temporal bone have been termed as Zygomatic air cell defect. [2] This entity is less known among the dental fraternity and was considered imperative to review to determine the variations among the different populations studied. Further, the differential diagnosis and complications of this entity were evaluated.
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??Materials and Methods |
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A literature search was conducted using Medline/Pubmed by using the keywords zygomatic air cell defect, pneumatized articular eminence and pneumatized articular tubercle, in English, German and French, for full text as well as abstracts. Also manual searching was conducted for the same based upon the cross references and abstract results.
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??Results |
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Definition
Zygomatic air cell defect has been defined as accessory air cells in the zygomatic process and articular eminence of the temporal bone which appear similar to the mastoid air cells and which does not extend further anteriorly than the zygomatico temporal suture. [3]
Nomenclature
The term zygomatic air cell defect was coined by Tyndall and Matteson in the year 1987 and the term pneumatized articular eminence was coined by the same investigators in 1985. [2],[4] The same has also been termed as pneumatized articular eminence and pneumatized articular tubercle. [4]
Development of temporal bone pneumatization
The pneumatized air cells are supposed to appear in the 22 nd -24 th weeks of fetal life. The pneumatization of mastoid cells begins at the 33 rd week and continues up to 8-9 years of life. The mastoid antrum, which is the biggest of the air cells, attains the adult size in the 35 th week. The development of air cells begins with the formation of bone cavities. The bone cavities contain primitive bone marrow which is transformed into mesenchymal connective tissue. The epithelial mucous membrane undergoes atrophy after invagination, leaving behind a thin membrane attached to the periosteum. Microscopically, an air cell is lined by a layer of epithelium and connective tissue constituting the mucous membrane of the air cell, which is separated from the underlying periosteum. [5] After the recession of the membrane and the resorption of the subepithelial bone, the air cells enlarge. [6]
The development of complete adult pneumatization has been divided into three stages: The infantile stage which is from birth to two years of age, the transitional stage, from 2-5 years of age and lastly the adult stage, which is after the age of 5 years. Once the adult stage is reached, pneumatization ceases. [5] Pneumatization of temporal bones is completed around the age of ten years. [7]
Functions of air cells
Though not clearly established, the following functions have been attributed for the air cells: [5],[6]
- Reception of sound
- Resonance of voice
- Protection from external violence
- Lightening the weight of the skull
- Insulation
- Acoustic dissipation
- The air reservoir function
The air reservoir of the middle ear function states that when the function of the ?Eustachian tube?More Details deteriorates, the air in the temporal bone acts to prevent negative pressure from developing due to absorption of air by the middle ear mucosa, thus preventing changes of the middle ear mucosa as well as progression of otitis media. [7]
Classification and distribution of temporal bone pneumatization
As early as 1934, Tremble reported the distribution of air cells in the temporal bone. He described ten locations within the temporal bone that can show pneumatization or the presence of air cells. This also included the zygomatic arch and the articular eminence. [3]
Virapongse and co workers quote the classification of temporal bone pneumatization proposed by Allam in 1969. According to them, temporal bone pneumatization is mainly divided into five regions as [5]
- Middle ear
- Squamomastoid
- Petrous apex
- Perilabyrinthine and
- Accessory areas
In the middle ear, areas that show pneumatization include the epitympanum, mesotympanum and the hypotympanum. [6]
The Squamomastoid part consists of two key areas of pneumatization, the mastoid antrum and the peripheral area. The mastoid antrum lies superiorly. Inferiorly and laterally the antrum extends downward in the direction of the mastoid tip, forming an oblong space called the central tract. Immediately surrounding the mastoid antrum are the periantral cells. [5]
The petrous apex consists of petrosal cells and apical cells. The petrous apex is often partly pneumatized by tracts derived from the supra and infralabyrinthine areas and from peritubal tract. [5],[6]
The perilabyrinthine areas further consists of supralabyrinthine and infralabyrinthine regions. The supralabyrinthine region is pneumatized by the posterosuperior and subarcate cell tracts of the mastoid antrum. The infralabyrinthine region is pneumatized by buds of pneumatization from the hypotympanum. [5],[6]
Accessory areas where air cells can be found, with their respective names, include the zygomatic cells, occipital cells, squmaous cells and styloid cells. The tegmental cells may pass upward into the squamous temporal region or extend into the zygomatic arch. [5]
Classification of ZACD
A classification of zygomatic air cell defect was proposed by Tyndall and Matteson in the year 1985. They classified ZACD into three types as
- Unilocular type [Figure 1]
- Multilocular type [Figure 2] and [Figure 3]
- Ttrabecular type
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Figure 1: Panoramic radiograph showing unilocular ZACD on the right side
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Figure 2: Panoramic radiograph showing multilocular ZACD on the left side
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Figure 3: Panoramic radiograph showing multilocular ZACD on the right side
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ZACD presents as asymptomatic, non-expansile, nondestructive radiolucency. Unilocular varient appears as an oval radiolucent defect with well defined borders and the multilocular one demonstrates numerous small cavities within and resembles mastoid air cells. The trabecular variety is basically a multilocular entity with internal bony striations. [3],[8]
Case reports on ZACD
Tyndall and Matteson quote a case report by Roser et al. [9] , in which pneumatization of zygomatic arch which was incidentally observed on panoramic radiograph obtained for the examination of temperomandibular joint. In their case, one large air cell was present extending from temporal bone into the zygomatic process. [4]
Andersen V in 1984 reported the Frequency of cyst-like pneumatization of the articular eminence on panoramic radiographs and probably it is the first survey to detect the prevalence of this entity. The results of this study are not available for review. [10]
Yurosko in 1985 reported a case of pneumatized articular eminence that was observed on a panoramic radiograph taken prior to extraction of third molar tooth in an 18-year old female patient. [11]
A case report by Piette E in 1986 suggests that pneumatization of articular eminence of the temporal bone is a radiographic finding only without any signs clinically. Further he says that it can be unilocular or multilocular and it affects both the genders. He also states that no treatment would be necessary for this entity but it jeopardizes some surgical procedures of the temperomandibular joint, when detected. [12]
Tyndall and Matteson in 1987, reported cases of zygomatic air cell defect in three of their patients in whom panoramic radiographs were obtained as a routine screening radiograph. In the three cases, ZACD was seen as radiolucencies in the zygomatic process of temporal bone and were non expansile and non-destructive. None of their patients had any symptoms regarding the lesion. In one patient, additional radiographs such as a Submentovertex view and waters view showed the presence of the air cells and did not provide any additional information. They also suggested that panoramic radiograph appears to be a suitable means for identification of ZACD. [4]
In 1989 a case was reported of pneumatized articular eminence by Randzio J The details are not available. [13]
Deluke in 1995 reports a case of unilateral ZACD observed on panoramic radiograph on the left side of the articular eminence, in a 16-year old male patient, which was found by chance. computed tomography (CT) scan was later obtained to rule out other disease process which showed extensive pneumatization of the temporal bone. A magnetic resonance image (MRI) was performed further to rule out the presence on any mass within the lesion, the details of which are not available. [14]
Hasnaini M and Yee S report a case in the year 2000; of bilateral ZACD observed on a panoramic radiograph, found incidentally in an 18-year old male patient who reported with temporomandibular joint (TMJ) dysfunction. Further, a CT scan was obtained which showed the presence of extensive pneumatization of all the parts of temporal bones which included the mastoid, petrous and zygomatic processes. The authors concluded that ZACD was not the cause of TMJ dysfunction and the same was managed conservatively which abated the symptoms. [15]
Stoopler and co workers in 2003 report a case of ZACD in a 53-year old female patient who had presented with facial pain. A panoramic radiograph showed extensive pneumatization of the zygomatic arch. To rule out the presence of pathology such as giant cell tumor or myxoma, further investigation-A CT scan was obtained, which revealed extensive pneumatization of the right temporal bone with pneumatization extending into the right zygomatic arch including the articular eminence. The authors concluded that the pneumatization was not the cause of facial pain. [8]
Koudstaal MJ, van der Wal KG in 2003 reported a case wherein a panoramic radiograph showed a radiolucency in the articular eminence which was considered as pneumatized articular tubercle (PAT) and later a CT scan confirmed the entity. [16]
Robert Reti, William Gilmore and Daniel Oreadi in 2012 report a case of ZACD detected on panoramic radiogrpahs in a 16-year old male patient who had reported for extraction of his third molars. Further, a CT scan was performed to differentiate this form other pathologies, confirmed the nature of the entity to be nothing but extension of the pneumatization of the temporal bone. [17]
Research on ZACD
Tyndall and Matteson in 1985 conducted the first detailed study on population distribution and radiographic appearance of ZACD. Their study consisted of 1061 dental school outpatients on whom panoramic radiographs were made. ZACD was found in 28 patients i.e. 2.6% of the population. The age range was of 15-74 years with a mean age of 32.5 years. No gender predilection was found in their study, 17 (53.1%) cases showed unilocular type of ZACD and 15 (46.9%) multilocular. ZACD was bilateral in 5 patients. Mean age, age range or sex distribution of the study samples was not given by the original authors. [18]
A study on ZACD conducted by Kaugars G, Mercuri L and Laskin D in 1986 wherein routine panoramic radiographs of 784 patients were evaluated retrospectively for the presence of pneumatization of the articular eminence. The radiographs of eight patients showed signs of PAT. These eight patients ranged in age from 32-69 years, and 4 patients showed bilateral PAT. They concluded that the use of tomography is recommended before surgical events involving the eminence to determine the extent of the pneumatization. [19]
Tyndall and Matteson gave a concise synopsis of reported cases of ZACD until 1987. The summary consisted of 5 reported cases. The authors opined that ZACD is discovered in young adults with a mean age of 23.4 years, with no sex predilection (M:F: 3:2). Two cases each was found on the right and the left sides of the Zygomatic process of temporal bone and only one case showed bilateral involvement. No information regarding the type of ZACD is obtainable in their case series. [4]
Carter LC, Haller AD, Calamel AD and Pfaffenbach AC carried out a study in 1999 to determine the prevalence and characteristics of ZACD on dental outpatient population. They obtained 2734 panoramic radiographs. The sample consisted of 1261 males and 1473 females. The average age for the study subjects was 41.4 years. The age range of subjects was 4-91 years. ZACD was found in 40 cases making the total prevalence of 1.5%. Half of the subjects were males and the other half females (50%) and hence no gender predilection was noted. ZACD was observed to be unilateral in 32 cases and 17 were seen on the right side and 15 were on the left. In 8 cases, ZACD was bilateral. [20]
A study conducted to determine relationship of pneumatised spaces of temporal bone with temporomandibular joint (TMJ) on computed tomography scan was done in 1999. The study sample consisted of 100 subjects with no clinical symptoms of TMJ abnormalities. The extent of temporal bone pneumatization was determined for both the sides. Pneumatization was recorded in the following structures: Roof of the glenoid fossa, articular fossa, articular eminence, zygomatic process and the peritubular area. Pneumatization up to the roof of the glenoid fossa was observed in 51 subjects; up to the articular eminence in 12 subjects and into the zygomatic process in 5 subjects. The authors detected that all subjects with pneumatization in articular tubercle and zygomatic process had a pneumatized glenoid fossa. [21]
A study conducted by Hofmann T and co workers in 2001, conducted to determine the prevalence and characteristics of ZACD. Panoramic radiographs were obtained of 1084 dental patients. The sample consisted of 628 male subjects and 456 females. ZACD was found in 20 subjects making the prevalence to be 1.85%. The mean age for the subjects in whom ZACD was found was 43.2 years with a range of 7-87 years. Eleven patients were males (55%) and 9 subjects were females (45%). Unilateral ZACD was observed in 16 cases with 7 on the right side and 9 on the left. Bilateral ZACD was observed in 4 (20%) of the subjects. The authors found no gender predilection among their study sample. The youngest patient in their study was aged 7 years. The authors do not classify ZACD as unilocular, multilocular or trabecular patterns. [22]
Park YH et al., studied, in 2002 the radiographic patterns of ZACD on 1400 subjects. They divided the study subjects into 7 groups by decade, from 9-60 years. Each group consisted of 200 subjects. The average age for the 1400 subjects was 35.2 years. There were 658 males (45%) and 742 females (53%) in the study population. The investigators found 31 cases of ZACD representing a prevalence of 2.2%. The mean age for subjects with ZACD was 27.5 years. ZACD was found in 22 males and 9 females. The male to female ratio was 2.4:1. The authors state that they found more cases with ZACD in the third decade and the incidence decreased after third decade. ZACD, in their study was not noted until 9 years of age and was not found after the age of 60 years. Unilateral ZACD was found in 24 cases (77%) with 50% of them on the right side. Bilateral ZACD was found in 7 cases (22%). The authors also classified ZACD into unilocular and multilocular types and 26 (68.4%) ZACDs were of unilocular type and 12 (31.6%) were multilocular. [3]
Orhan K and coworkers in 2005 studied the prevalence and variations of ZACD on 1006 panoramic radiographs. The average age of the study subjects was 36.7 years with age range from 10-90 years. There were 388 (38.6%) males and 618 (61.4%) females. The mean age for male subjects was 37.1 years while the mean age for females was 36.4 years and the age range was 10-90 years. ZACD was found in 19 subjects giving a prevalence of 1.88%. A Female predilection was found with 12 (63.1%) cases occurring in them while 7 (36.9%) occurred in males. Unilocular ZACD was found in 12 with 10 on the right side and 2 on left. Bilateral ZACD was found in 7 subjects. Unilocular type of ZACD was observed in 10 and 16 were multilocular. [19]
In 2005 a meta analysis of 6 studies published previously than 2005 to evaluate ZACD on panoramic radiographs was done. The total number of subjects were 7870 and age ranged from 6 and 97 years. A total of 169 ZACD was detected making the prevalence to be 2.32%. Out of the subjects female constituted 56.12%, and males 43.9%. Most ZACD were found to be unilateral (70%). They also gave a forensic twist to their study by stating that ZACDs can serve for personal identification when found on panoramic radiographs. [23]
Orhan K, Delilbasi C and Orhan AI conducted a study to find the prevalence of ZACD in pediatric population, in 2006. Panoramic radiographs of 1049 children were evaluated which consisted of 510 males and 539 female subjects. Twenty four ZACDs were found in 17 subjects representing a prevalence of 1.62%. Unilocular ZACD was observed in 10 subjects whereas multilocular ZACD in 14 subjects. [2]
Another study consisting of a very large sample size totalling to 8107 patients was done in 2009. Interpretation of panoramic radiographs were made on the side and radiographic appearance of the PAT; and gender and age of patients. Eighty three of 8107 (1.03%) individuals had PAT with 41 females and 42 males. PATs were located on the right side in 60 individuals and in the left side in 50 individuals. They were unilateral in 56 cases and bilateral in 27 (totally 110 PAT). Forty four of them were unilocular type, and 66 were multilocular type. It concluded by saying treatment of PAT is unnecessary. However if a surgeon who is planning to perform surgeries like minoplasty or eminectomy on a patient who has PAT, he/she should be aware of the details of PAT. Moreover, fractures of the temporal bone with PAT can occur more easily than temporal bone without PAT. [24]
An Indian prospective study to determine the prevalence, patterns of occurrence and variations of zygomatic air cell defects (ZACDs) using panoramic radiographs was done in 2010. Panoramic radiographs of 600 outpatients were examined to evaluate the variations and characteristics of ZACDs, wherein ZACDs were identified in 15 subjects out of 600, giving an overall prevalence of 2.5%. Seven ZACDs were seen in males and eight in females. Among the 15 ZACDs, 9 were unilateral and 6 were bilateral. The authors concluded that the overall prevalence of ZACD is relatively low in South Indian population and vigilant radiographic evaluation is needed to identify these entities. [25]
Another study to determine the prevalence and characteristics of pneumatized articular eminence (PAE) in dental patients using cone beam computed tomography (CBCT) with respect to age, sex, and type of skeletal anomaly was done in 2010. A retrospective study of 603 orthodontic patients aged between 6 and 24 years was performed using sagittal and coronal CBCT images. The age, gender, skeletal anomaly, and laterality were recorded for all patients, and the types were noted for cases of PAE. Sixty four PAEs were found in 39 orthodontic patients, representing a prevalence of 6.47%. No significant differences in sex (P = 0.153), age (before and after puberty, (P = 0.389), and type of skeletal anomaly were observed (P = 0.271). They concluded that clinicians must be aware of these structures to avoid complications in cases for which surgery is planned and recognize its role in the onset or continuation of temporomandibular joint dysfunction. [26]
A study to investigate the prevalence and characteristics of pneumatized articular tubercule (PAT) in an orthodontic patient population and to examine the possible correlations between different orthodontic malocclusions and pneumatized articular eminence types was conducted in 2010. Pre-treatment panoramic radiographs were evaluated retrospectively of 1405 children and adolescents (459 boys and 946 girls) having various types of malocclusions. The diagnostic criteria of PAT adopted by the authors was only if unequivocal pneumatization of the articular eminence could be seen or if the defect was located in the articular eminence posterior to the zygomaticotemporal suture, as a well defined unilocular or multilocular radiolucency. PAT was classified as unilocular or multilocular and unilateral or bilateral. Suitable statistical analysis was applied Sixty six pneumatized articular eminences were found in 48 patients, representing a prevalence of 3.42%. The results of Chi-square test showed no statistically significant differences considering age (P = 0.516), gender (P = 0.719), type of malocclusion (P = 0.155) and localization (P = 0.738). A relatively high rate of pneumatized articular eminence was observed among patients with orthodontic malocclusions (3.42%) when compared to the general population studies. They concluded by stating that knowledge about these structures is important for the interpretation of panoramic radiographs as it provides information prior to temporomandibular joint surgery and help to avoid intra-operative reconstruction and complications. [27]
Recently in 2011, a study done to detect the prevalence and characteristics of ZACD on CBCT was done. This newer imaging technique showed the pneumatization better than the conventional technique and hence a higher prevalence of 8% which the highest reported to date. Most of the ZACDs were found in female subjects while multilocular variant was more common (about 58%). The authors concluded that ZACDs are more common than previously thought and for suspected cases supplemental CBCT evaluation should be done. [28]
A research from India in 2012, involved retrospectively evaluating 7755 panoramic radiographs with the intention of assessing the prevalence of zygomatic air cell defect (ZACD) and establishing its dominant location and type is available in the literature. Panoramic radiographs of routine outpatients aged between 19 and 91 years were concomitantly evaluated by four investigators for estimating the prevalence and characteristics of the zygomatic air cell defect. The prevalence of ZACD was noted to be 1.82%, with male preponderance. Unilateralality and multilocular appearance of ZACD were the dominant patterns observed. [29]
Findings of research
To summarize the results of all the studies done so far shows that the prevalence of ZACD varies from 1.03-8%, based on the imaging modality used and the population studied. Literature on gender preponderance shows that ZACDs can be noted in both the genders with a higher prevalence in males or females. Age range in which ZACDs can be detected is large, from 7-75 years. The appearance of ZACDs radiographically can be either unilocular or multilocular, and dominance of the appearance as well as the side preference differs.
Additional radiographic views to visualize ZACD
It is stated that the other plain radiographic views such as Waters view, Towne's view and Sub-mento vertex view do not provide adequate visualization of the posterior aspect of the zygomatic arch and hence not recommended. Transcranial projection of TMJ also does not provide complete and adequate visualization of zygomatic arch. If further and better visualization of ZACD is necessary, then computed tomography or cone beam computed tomography is advocated. [20],[28]
Consequences of violation of ZACD
Kulikowski BM and co workers report a case where ZACD was encountered surgically, in a patient for whom bilateral articular eminectomy procedure was being done for the symptoms of recurrent temperomandibular joint dislocation. Post-operatively, the authors performed a computer tomography which showed extension of pneumatized mastoid air cells into the articular eminence. [30]
It stated that the temporal air spaces are potential pathways for the spread of various pathological processes. Tumors of the mastoid process and ear may extend into temperomandibular joints whereas otitis or mastoiditis may involve temperomandibular joints and can even result in ankylosis. Preoperative demonstration of ZACD serves as a contraindication for performing eminoplasty or eminectomy to treat recurrent mandibular dislocation. Orhan and co-workers quote Lindenmuth and Clark, who opined that the surgeons planning procedures should be aware of the details of pneumatized articular eminence. During surgeries, surgeons should take care to avoid accidental penetration through the defect, which may result in dural tear and leakage of cerebrospinal fluid. [19]
Carter and co-workers quote Sanders who pointed out that pneumatizations exposed during eminectomies can serve as potential avenues for cranial sepsis and infection. [20]
Pneumatized articular eminences or ZACDs can even be violated during maxillofacial trauma. Fracture or dehiscence of the glenoid fossa may lead to herniation of soft tissue contents into middle ear and further result in middle ear infections and mastoid effusion. [8] It is affirmed that if pneumatization of the articular eminence is demonstrated on the preoperative radiograph, alternate surgical therapy is indicated to eminectomies. [20]
Differential diagnosis
Numerous central pathologies have been identified and their radiographic features have been fairly well described in the past. Variations are known to occur in the clinical features and their radiographic appearance.
A very few central pathologies have been recognized to have involved the zygomatic processes of the temporal bone. The differential diagnosis for ZACD includes; aneurysmal bone cyst, central or osseous hemangioma, central giant cell tumor, eosinophilic granuloma, fibrous dyspalsia and metastatic tumors. [3],[4],[19],[20]
The aneurysmal bone cyst (ABC) is considered a pseudo cyst as it does not possess an epithelial lining. It is reported most frequently in the long bones, the vertebrae and occasionally the jaw bones. It is believed that, it forms as a continuum with the traumatic bone cyst and the central giant cell granuloma. Aneurysmal bone cyst is a slow growing lesion. It frequently involves persons under the age of 20 years and around 93% of them occur in the first three decade of life. As it is a slow growing lesion, it expands the cortices but usually does not destroy them. No gender predilection has been observed. Most often, ABC is a solitary lesion. Radiographically, the lesion appears as either a well defined unilocular or multilocular radiolucency. [30] Carter LC and coworkers state that ABC of the zygoma presents as a swelling with pain and on radiographic examination, it presents as expansile radiolucency. [20]
Vascular malformations of the bone are uncommon but occur frequently on soft tissues. Histologically, the capillary type of hemangioma is the most common form of hemangioma. Most of the lesions of central hemangioma are evident in the first year of life and at birth and quite a few in first two decades of life. Females are affected more commonly than males. Central hemangiomas have a predilection for vertebral column, calvarium and long bones. The lesions cause asymmetry due to the swelling that they cause and the skin may be warmer to touch and of purplish or bluish in color. Other signs may be swishing noises, tinnitus or impaired hearing, blurred vision and epistaxis. [20]
Hemangiomas involving the zygomatic bone is extremely rare and only 22 cases have been reported so far, most of them occurring in the infra-orbital masses, and none in the zygomatic arch. Radiographs reveal a unilocular or multilocular, often honeycomb, expansile radiolucency. [20],[31]
Fibrous dysplasia is a nonneoplastic, hamatomatous developmental lesion of the bone of unknown etiology. It is characterized by replacement of bone with fibro-osseous tissue. Fibrous dysplasias are divided into two basic types; a monoostotic type and a polyostotic type. The polyostotic type of the disease is further divided into craniofacial fibrous dysplasia, Jaffe type and Albright's type. Fibrous dysplasia of the cranio facial type can involve the sphenoid bone, frontal bone and the zygoma. There is one report of fibrous dysplasia involving the zygomatic arch. [20],[31]
Whenever the temporal bone is involved, most of the times, all the parts the bone such as the squamo-tympanic, mastoid etc., are involved. The most common presenting symptom of fibrous dysplasia of temporal bone includes progressive loss of hearing, gradual swelling and change in the contour of the temporal bone and progressive obliteration of external auditory meatus. Radiographic features vary with the level of maturation of the disease wherein the early lesions may appear as radiolucencies or a lesion with increased bone density giving a ground glass appearance or an orange peel appearance. [20],[31]
Histiocytosis X is a group of nonlipid histiocytosis characterized by proliferation of histiocytes in which no heritable disorder of lipid metabolism is demonstrable; the cause is unknown. This disease has been classified as Letterer-siwe disease, Hand-Schuller-Christian disease and eosinophilic granuloma. [20],[31]
Involvement of temporal bone by eosinophilic granuloma is rare with reports on 30 cases. Eosinophilic granuloma of the temporal bone erodes the mastoid cortex, destroys the tegman and then the semicircular canals and the cochlea. Radiographically, the lesion presents as a well demarcated, expansile radiolucency with a characteristic bevel edged appearance. [20],[31]
Malignant cells from the primary site are carried via arterial blood or through the lymphatics and result in metastasis. Metastasis can radiographically show several appearances which includes; a) A solitary, well defined cyst like radiolucency, caused by tumors which are slow growing and well differentiated or in patients in whom successful treatment with cytotoxic drugs have been used, b) A solitary, poorly defined radiolucency caused by localized, rapidly growing tumor, c) Multiple, separate, poorly defined radiolucencies consisting several foci of malignant nests growing separately, d) Multiple punched out radiolucencies caused by several nests of slow growing tumor cells located close to each other in the bone. [20],[31]
The lesion can show a predominantly radioopaque appearance in which the tumors induce osteoblastic activity or an irregular salt and pepper appearance in which the tumor is widely disseminated in multiple nests in the bone. [20],[31]
A case of prostate malignancy metastatic to zygomatic arch, where in hyperostosis was evident radiographically, is also available in the literature. [20],[31]
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??Conclusion |
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Zygomatic air cell defect or pneumatized articular eminence is a variant of normal anatomy. This entity was described and studied as early as 1985, in a detailed manner. Numerous researches are available describing the variations in appearance of this normalcy and the population distribution. It appears, from this review that the prevalence ranges from 1-8%, higher when advanced imaging modalities such as CBCT is used. Although two interesting cases of incidental discovery of ZACD in patients who had symptoms of oro-facial pain and TMJ dysfunction is available, no study has been taken up to detect any correlation between the symptoms and ZACDs. Further, there is no clear dominance of this entity with regard to gender, side or age. But the only consistent feature is the radiographic appearance. The complications this entity can pose, when undetected, cannot be over emphasized. Recognition of ZACDs and differentiation from other pathologies by oral and maxillofacial radiologists, oral surgeons and general dentists is extremely important to prevent any untoward complications.
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