The application of Hounsfield units in the differentiation of odontogenic benign lesions: A systematic review :Luciana Munhoz, Emiko Saito Arita, Journal of Oral and Maxillofacial Radiology

SYSTEMATIC REVIEW
Year : 2021 | Volume : 9 | Issue : 3 | Page : 71--79

The application of Hounsfield units in the differentiation of odontogenic benign lesions: A systematic review

Luciana Munhoz, Emiko Saito Arita
Department of Stomatology, Dentistry School, São Paulo University, São Paulo, Brazil

Correspondence Address:
Luciana Munhoz
Department of Stomatology, Dentristry School, São Paulo University, 2227 Lineu Prestes Avenue, São Paulo 05508-000
Brazil

Abstract

Context: Odontogenic lesions comprise a broad range of cysts and neoplasms. Often, multislice computed tomography (MCT) is requested before odontogenic lesions surgical treatment. Hounsfield units (HU) are a quantitative measurement of tissue radiodensity that could be applied in the differentiation of these lesions. Aims: This systematic literature review addresses the use of HU obtained by MCT in the evaluation of benign odontogenic lesions. Materials and Methods: Databases were searched and original research studies or case report manuscripts published up to April 2021 were included. The keywords “MCT” OR “multidetector computed tomography” OR “helicoidal computed tomography” OR “Hounsfield” OR “computed tomography number” combined with the keywords “maxillofacial pathology,” “oral pathology,” “dental tissue neoplasms,” “odontogenic cysts” were used, “odontogenic tumors,” and the histological denomination of benign odontogenic lesions according to the World Health Organization classification was applied. Only English language manuscripts and studies pertaining to HU were selected. Results: Nine investigations (six original articles and three case reports) regarding distinct benign odontogenic lesions were included in the review. Conclusions: The application of HU as a complementary tool in the assessment of odontogenic lesions is little explored by researchers but could be a useful tool in the differentiation of odontogenic lesions as the few studies available in the literature have already succeeded in differentiating between specific types of lesions. This systematic review is registered at the National Institute for Health Research International Prospective Register of Systematic Reviews (PROSPERO). Registration number: CRD42019116888.

How to cite this article:
Munhoz L, Arita ES. The application of Hounsfield units in the differentiation of odontogenic benign lesions: A systematic review.J Oral Maxillofac Radiol 2021;9:71-79

How to cite this URL:
Munhoz L, Arita ES. The application of Hounsfield units in the differentiation of odontogenic benign lesions: A systematic review. J Oral Maxillofac Radiol [serial online] 2021 [cited 2023 Mar 28 ];9:71-79
Available from: https://www.joomr.org/text.asp?2021/9/3/71/335733

Full Text

Introduction

Odontogenic lesions comprise a broad range of cysts and neoplasms that originate from the remnants of the tooth-forming organ within the maxillary or mandibular alveolus. At the first diagnosis, these lesions are frequently observed by panoramic radiographs, which is extremely useful in the general evaluation of the lesions; however, there are some limitations inherent to bidimensional techniques. Hence, computed tomography is often requested to further imaging examination and treatment planning.[1]

In dentistry, cone beam computed tomography (CBCT) is widely used in odontogenic lesion assessment; nevertheless, multislice computed tomography (MCT) can also be employed. MCT has great spatial resolution and bone tissue contrast, which allows the study of lesions and adjacent structures involvement. In addition, MCT provides information about Hounsfield units (HUs), which is useful in the determination of lesion density.

HUs are a quantitative measurement of tissue radiodensity, expressing the tissue attenuation or absorption coefficient of the X-rays in a numerical gray scale, which is proportional to the physical density of the tissue.[2] In the Hounsfield linear scale, the 0 HU value is defined as water and-1000 HU value is defined as air. The HU value attributed to a tissue type in the Hounsfield scale depends on the density of the tissue: the higher the density of a tissue paired with a higher X-ray absorption, the brighter the tissue will appear in the MCT examination, resulting in a positive and higher HU value; the lower the density of a tissue paired with a lower X-ray absorption, the darker the tissue will appear in the MCT examination, resulting in a negative and lower HU value.

Considering that lesions or pathological alterations radiodensity assessed using CT varies according to the tissue attenuation, the use of HU values in the measurement of tissue density has been applied in distinct areas of medicine, as well as in dentistry, for the differentiation of various lesions or pathological conditions, providing great benefit for imaging interpretation and diagnosis.[2]

The application of HU in odontogenic lesion assessment has been investigated, as MCT may also be requested before surgical procedures. Thus, the objective of the present study was to review the literature regarding the application of HU in the evaluation of benign odontogenic cysts and neoplasms. The following questions were addressed: (1) what has been investigated regarding the application of HU in the study of benign odontogenic cysts and neoplasms? (2) what were the main results? and (3) what is the potential application of HU in evaluating diagnoses of odontogenic lesions?

Materials and Methods

Protocol and registration

This systematic review is registered at the National Institute for Health Research International Prospective Register of Systematic Reviews (PROSPERO). The registration number is CRD42020165292. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist was followed.[3]

Data selection

The selection of studies potentially eligible for inclusion in the present systematic review was accomplished using the PubMed Central (United States National Institutes of Health's National Library of Medicine), EmBase (Excerpta Medica Database), CENTRAL (Cochrane Central Register of Controlled Trials), Web of Science (Institute for Scientific Information–Clarivate Analytics), Scopus (Elsevier), and Google Scholar (Google) databases. The aforementioned databases were searched for articles in English and papers published as recently as April 2021 were included. The Boolean operator “AND” was used to combine the searches. Itemized search approaches were settled upon for each database on the basis of the following search keywords: “Odontogenic tumors” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “dental tissue neoplasms” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontogenic cysts” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “maxillofacial pathology” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “oral pathology” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield OR computed tomography number;” “ameloblastoma” AND “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “squamous odontogenic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “calcifying epithelial odontogenic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “adenomatoid odontogenic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “ameloblastic fibroma” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “primordial odontogenic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontoma” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “dentinogenic ghost cell tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontogenic fibroma” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontogenic myxoma” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “cementoblastoma” AND “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “cemento-ossifying fibroma” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “radicular cyst” AND “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “inflammatory collateral cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontogenic keratocystic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “odontogenic keratocyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “radicular cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “inflammatory collateral cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “dentigerous cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “lateral periodontal cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “botryoid odontogenic cyst” AND “helicoidal computed tomography;” “glandular odontogenic cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “calcifying odontogenic cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” “orthokeratinized odontogenic cyst” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number;” and “gingival cyst” AND “helicoidal computed tomography” OR” MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number.” As odontogenic keratocysts were previously named “keratocystic odontogenic tumors,” the keywords “keratocystic odontogenic tumor” AND “helicoidal computed tomography” OR “MCT” OR “multidetector computed tomography” OR “Hounsfield” OR “computed tomography number” were also considered in the search.

A summary of the data selection is available in [Figure 1]. [Figure 2] shows the PRISMA flow chart with the selection strategy.[4]{Figure 1}{Figure 2}

Eligibility criteria – Inclusion and exclusion of studies

Types of studies

Research studies and case reports were considered for inclusion, whereas literature reviews, abstracts, and oral presentations were excluded. Research investigations and case reports using MCT that did not consider HU were not considered to be eligible, as well as nonenglish language and nonhuman studies.

Participant groups

Research investigations and case reports related to groups or cases of odontogenic benign lesions with MCT examinations that applied or described HU were included in the data selection.

Data extraction

Data extraction was performed by two independent reviewers who initially screened the titles and abstracts and then analyzed the full text. A third consultant verified each study to determine if the study was eligible. Disagreements between the reviewers were solved by discussion. All publication dates were included up until April 2021. Articles not found in the databases of the authors' of the present review university were asked to the researchers; in case. Absence of response and the inability to access the full text of a study also resulted in exclusion.

Data analysis–Risk of bias

The data search according to the keywords and screening results is summarized in [Figure 1]. The searches for specific lesions were combined on the basis of their World Health Organization histological classification [e.g., searches for ameloblastomas, squamous odontogenic tumors, calcifying epithelial odontogenic tumors, and adenomatoid odontogenic tumors are included under the headings “Benign odontogenic neoplasms” and “Benign odontogenic cysts” in [Figure 1]]. In [Table 1], [Table 2], [Table 3], general and HU-related data regarding the included studies are exhibited.{Table 1}{Table 2}{Table 3}

The HU values were not compared directly, as HU values may be subject to several sources of variability, such as differences between scanners, manufacturers, calibration, or methods; variation in the spectra of the X-ray beam due to distinct degrees of filtration before the beam exits the tube housing; the amount of scatter radiation that achieves the detectors; differences in convolution kernels used by different manufacturers; and differences in patient positioning.[14],[15]

Results

A total of 3809 studies were initially identified using all keywords. After the inclusion and exclusion criteria were applied and the repeated manuscripts were removed, 3801 studies were excluded. A final total of nine manuscripts[5],[6],[7],[8],[9],[10],[11],[12],[13] regarding the use of HU from MCT in the investigation of odontogenic benign cysts and neoplasms were included [Table 1]. A flow diagram illustrating the literature search results is available [Figure 1].

The following data were extracted and exposed: author information, publication year, location where the study was performed, type of study (case report or research study), number of cases assessed, and MCT equipment. Six research studies[5],[7],[9],[10],[12],[13] and three cases reports[6],[8],[11] were selected. The oldest manuscript was a research study from 2002,[13] and the most recent was a case report from 2020.[5] The number of cases assessed in the research articles ranged from nine[10] to 307.[5] Six studies were conducted in Japan[5],[7],[8],[9],[10],[13] and the MCT equipment manufacturer and model were heterogeneous. The aforementioned information is detailed in [Table 1].

The types of odontogenic lesions included in the study samples were also extracted [Table 2]. Dentigerous cysts,[5],[6],[7],[13] ameloblastomas,[7],[9],[12],[13] odontogenic keratocysts,[5],[9],[12],[13] calcifying odontogenic tumors,[7],[10] adenomatoid odontogenic tumor,[7] odontogenic fibroma,[7] complex odontoma,[7] calcifying odontogenic tumor associated to adenomatoid odontogenic tumor[8] follicular cyst[9] were the odontogenic lesions presented in the study samples. The aforementioned lesions were compared to inflammatory lesions, as radicular cysts in two investigations.[5],[9]

The lesions assessed, study objectives, and main imaging features of the lesions reported are also listed in [Table 2]. The case reports focused on demonstrating unusual lesions, such as a dentigerous cyst in a 3-year-old child,[11] a dentigerous cyst with a multilocular pattern in plain radiographs,[6] and a calcifying odontogenic tumor associated with an adenomatoid tumor.[8] The research articles essentially aimed to verify the use of MCT in odontogenic lesion differentiation and characterization, although Uehara et al.[5] strongly emphasized the usefulness of HU values and differentiation between MCT equipments. Furthermore, summarized data regarding lesion MCT imaging features were collected and presented in [Table 2]. Overall, odontogenic lesions were displayed as present in uniloculated areas with a hypodense pattern, except for lesions with calcified areas.

HU values for benign odontogenic cyst neoplasms are available in [Table 3]. The lower HU value reported was related to dentigerous cyst margins (3.9 HU)[6] and the higher HU value was related to an odontoma (2540 HU).[7] One study presented the data in graph only, and the HU values could not be included in [Table 3] due to the impossibility of describing precise numbers.[9] Information regarding the results and conclusions of the selected studies are available in [Table 3].

Two figures from author's collection were provided to illustrate this review. In [Figure 3], a case of ameloblastoma is demonstrated in axial, sagittal, and coronal slices. [Figure 4] shows an example of region of interest (ROI) and HU measurements in the center and in the lesion margin. Note that the lesion center (ROI1) has as hyperdense area and higher HU values when compared to the ROI2, in the margin of the lesion.{Figure 3}{Figure 4}

Discussion

In the present review, the main findings pertaining to the application of MCT and HU in the investigation of odontogenic lesions available in the literature are demonstrated. Although many studies performed MCT examinations in the assessment of odontogenic lesions, only a few applied HU for the characterization or differentiation of these lesions.[5],[12],[13]

Previously, HUs have been proven to be valuable for the evaluation of implant sites,[16] osteoporosis screening,[17],[18] neurological diseases,[19] and a number of other conditions. However, only a few studies have considered HU from MCT for odontogenic lesion diagnosis and diferentiation.[5],[12],[13] A possible reason for the low number of documents may be due to the fact that CBCT is more popular than MCT in dentistry. In fact, CBCT has some advantages over MCT, such as a lower cost, easy access for dental professionals, and the capability of providing multiplanar images that deliver a lower radiation dose when compared to MCT;[20] nevertheless, CBCT may present poor soft tissue contrast[21] due to the low radiation dose and, of course, the impossibility to apply the Hounsfield scale in the evaluation of lesions.

Overall, the investigation concluded that HUs were useful in the specific differentiation of odontogenic lesions, particularly dentigerous cysts with dystrophic calcifications from other odontogenic neoplasms.[7] Frequently, dentigerous cysts present as hypodense areas without hyperdense materials within the lesions.[7] Although it is still uncertain, it is hypothesized that calcifications may originate from dental follicle mesenchymal cells with the capacity for differentiation in cementoblasts and osteoblasts, which produce calcifying matrices.[22] The presence of calcifications may resemble odontogenic tumors, and researchers can succeed in differentiating dentigerous cysts from dystrophic calcifications using MCT.

Dissimilarly, the differentiation of odontogenic cysts from cystic-appearing tumors in the mandible, such as ameloblastomas or keratocyst odontogenic tumors (in the years of publication of the selected studies, keratocysts were classified as tumors) was not possible using HU from MCT.[9] However, specifically considering ameloblastomas, this type of lesion presents a wide range of variants with distinct imaging features, often classified in radiology as “solid or cystic,” which were not considered in order to achieve the aforementioned results, although investigators considered – to make comparisons between lesions – the maximum MCT value.[9]

One of the selected studies[12] observed that solid ameloblastomas exhibited a higher HU value in the central slices than in the peripheral slices, which demonstrates that this odontogenic lesion has an heterogeneous internal content. Although the researchers verified that solid ameloblastomas had higher HU values than unicystic variants, it was not statistically significant – likely due to the limited sample size assessed (a total of nine cases).

The differentiation between odontogenic keratocysts from dentigerous cysts and radicular cysts was demonstrated by Uehara et al.,[5] which also discussed that MCT scanners can demonstrate distinct HU values according to the type of the equipment.

The case reports also added information to this review,[6],[8],[11] when describing the HU values of the rare odontogenic lesions reported, or demonstrating the usefulness of HU values in the differentiation of odontogenic lesions.[6]

The few studies available, with their lack of heterogeneous protocols and standardization for HU measurements for the distinct lesions, was considered to be a limitation for this review and a limitation to the determination of HU values for each odontogenic lesion, to collaborate with MCT diagnosis of odontogenic lesions.

Conclusions

The application of HU as a complementary tool in the assessment of odontogenic lesions is little explored by researchers but could be a useful tool in the differentiation of odontogenic lesions, as the few studies available in the literature have already succeeded in differentiating between specific types of lesions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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