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1 Department of Radiology, Onze Lieve Vrouwe Gasthuis, PO Box 95500, Amsterdam
1090 HM, The Netherlands.
2 Department of Radiology, Leiden University Medical Center, Leiden, The
Netherlands.
3 Department of Pathology, Leiden University Medical Center, Leiden, The
Netherlands.
4 Department of Orthopedic Surgery, Leiden University Medical Center, Leiden,
The Netherlands.
Received February 17, 2004;
accepted after revision May 11, 2004.
Address correspondence to H.-J. Van der Woude.
Abstract
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MATERIALS AND METHODS. MR images of 22 patients with histologically proven adamantinoma, subtyped according to defined criteria, were analyzed, with emphasis on morphologic features, signal intensities, and enhancement parameters. Intra- and extraosseous tumor extent was determined. In all patients, examination of the corresponding resected specimens was performed with regard to tumor extent and presence of multicentricity. Moreover, radiographs were reviewed, and radiographic features derived from the literature were determined.
RESULTS. All tumors were primarily localized in the tibia diaphysis (including one patient with additional lesions in the fibula), most frequently in the anterior cortical bone (19/22) with extension toward the bone marrow in 12 patients. We distinguished two morphologic patterns: a solitary lobulated focus versus a pattern of multiple small nodules in one or more foci. Separated tumor foci, defined as foci of high signal intensity on either T2-weighted images or T1-weighted contrast-enhanced images, interspersed with normal-appearing cortical or spongious bone were seen in six patients. All tumors showed intense and homogeneous static enhancement, but there was no uniform dynamic enhancement pattern. No relationship between MRI features and histologic subtype of adamantinoma was found.
CONCLUSION. Some uniform MRI characteristics, along with those of radiography, may contribute to the diagnosis of adamantinoma; however, these are not related to the histologic subtype. MRI is pivotal for precise locoregional staging, especially for depiction of distant cortical foci, soft tissue, and intramedullary extension and thus is useful for determining tumor-free margins and strategies for reconstructive surgery.
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Careful wide en bloc resection of an adamantinoma is pivotal because
marginal or intralesional removal significantly increases the risk of local
recurrence (
32%) and of lung metastases ( 25%)
[5,
6]. In this respect, the
surgeon is often challenged by the multifocal appearance of the adamantinoma,
which may hamper the objective of optimal functional recovery. An optimal
preoperative staging procedure is therefore essential. In this respect,
findings of radiography alone may underestimate the true tumor extent. In
general, because of optimal soft-tissue contrast and multidirectional imaging,
MRI is the preferred technique for the staging of musculoskeletal tumors
[9].
In the literature, only incidental reports describe the MRI characteristics of adamantinoma [10–16]. In this article, MRI features based on a series of 22 patients and the role of MRI in the staging of adamantinoma are described. Special attention was paid to the multifocal appearance of the tumor and the differential diagnosis between the osteofibrous dysplasia-like and classic adamantinoma subtypes. The latter may be important because of the different clinical behavior of the histologic subtypes.
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Radiography
Radiographs with both posteroanterior and lateral projections were
available in 20 patients. The radiographic features that were determined were
derived from the literature
[8], and the results are given
in Table 2.
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Histopathology
The histologic diagnosis of adamantinoma was made in all patients after
biopsy, including immunohistochemical analysis using antibodies directed
against a broad variety of cytokeratins
[19]. Six patients had a
classic adamantinoma (median age of adamantinoma, 26.8 years), whereas in the
other 16 patients, a diagnosis of osteofibrous dysplasia-like adamantinoma
(median age of osteofibrous dysplasia-like adamantinoma, 16.1 years) was
established. Diagnosis of classic adamantinoma was made when clusters of
epithelial cells in various differentiation patterns predominated in an
osteofibrous background (Fig.
1A,
1B,
1C,
1D,
1E,
1F). The predominance of an
osteofibrous dysplasia-like pattern with the presence of scattered
keratin-positive epithelial tumor cells led to a diagnosis of osteofibrous
dysplasia-like adamantinoma
[6].
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In all resected specimens, special attention was paid to the potential multicentricity of the lesion, cortical involvement of the tumor, and the rate of bone marrow involvement. In all patients, MRI sections could be compared with histologic macrosections.
MRI
All patients finally selected for this study underwent MRI before surgery
of the primary tumor. The examinations were performed on a 0.5-T (n =
7) or a 1.5-T (n = 15) superconductive scanner. Spin-echo T1-weighted
(TR range/TE, 500–600/20) sequences were always available. Spin-echo
T2-weighted (TR/TE, 2,000/100) or turbo spin-echo (TR range/TE,
3,000–4,000/120) sequences with (n = 15) or without
fat-selective presaturation were performed in 21 of 22 patients. In 19 of 22
patients, spin-echo T1-weighted sequences after IV injection of contrast
medium (gadopentetate dimeglumine, Magnevist, Schering) with or without
fat-selective presaturation were performed, preceded by a dynamic
contrast-enhanced gradient-echo sequence with a temporal resolution of 3 sec
in 14 patients.
The following characteristics were evaluated in consensus by two observers and the results are given in Table 3.
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Tumor size.—The length of the tumors in the longitudinal direction, assessed on coronal or sagittal spin-echo T1-weighted images, was measured in centimeters.
Tumor localization.—The exact tumor site within a long bone (epi-, meta-, or diaphysis or all three) was assessed.
Cortical involvement and tumor margins.—Cortical involvement, defined as the presence or absence of abnormal signal intensity foci (intermediate on T1-weighted images and high on T2-weighted images) as opposed to the low signal intensity of the normal cortical bone, was assessed. Moreover, cortical thickening was recorded, and cortical breach was determined when outer cortical integrity was disturbed by the presence of abnormal (tumor) signal intensity.
Bone marrow involvement and tumor margins.—The absence or presence of bone marrow involvement, defined as abnormal signal intensity areas and foci (intermediate on T1-weighted images and opposed to the high signal intensity of normal bone marrow and high on T2-weighted images) was determined, and bone marrow involvement relative to cortical involvement was assessed in each patient.
Soft-tissue extension.—The presence or absence of tumor extending ahead of the margins of cortical bone and periosteum was recorded.
MRI macromorphology and multicentricity.—Distinction was made between a solitary lesion and the presence of a multifocal appearance (two or more tumor foci within one bone separated by normal-appearing cortical or spongious bone).
MRI micromorphology.—A distinction was made between a lobulated pattern of a solitary focus and a pattern of multiple small nodules in a single focus.
Signal intensity characteristics.—Signal intensities of tumor relative to muscle on spin-echo T1- and T2-weighted images (higher, equal, or lower) were determined.
Static enhancement.—The pattern of tumor enhancement on T1-weighted gadopentetate dimeglumine–enhanced images (absent, peripheral, or homogeneous) was recorded.
Dynamic enhancement.—Lesional enhancement within or after 6 sec relative to arterial enhancement on dynamic contrast-enhanced gradient-echo images was recorded; moreover, signal intensity–time curves were analyzed. A distinction was made between a pattern of rapidly progressive enhancement during the first pass of the contrast medium, according to the steepest part of the signal intensity–time curve, followed by an early plateau phase or washout versus gradual increase of enhancement [20].
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Cortical involvement.—Cortical thickening was seen in all patients. In all except three patients, tumor was seen within the anterior cortical bone (Fig. 4A, 4B, 4C, 4D). In three patients, only the posterior or posteromedial cortical bone was involved. In 12 (55%) of 22 patients, intracortical tumor without signs of cortical breach was seen on both MR images and corresponding histologic macrosections. Cortical breach, according to the predefined criteria, was seen on both MR images and corresponding histologic sections in seven (32%) of 22 patients. In the remaining three patients (14%), histology showed discrete cortical breakthrough, but this was not scored as such on the MR images. When related to histologic subtype, cortical breakthrough was seen in half of the patients with osteofibrous dysplasia-like adamantinoma and in two of six patients with classic adamantinoma.
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Bone marrow involvement.—In 20 (91%) of 22 patients, findings on MR images corresponded well with those of the histologic sections with regard to bone marrow extension of the intracortical tumor localization. In eight (40%) of these 20 patients, no bone marrow involvement at all was found. In 12 (60%) of 20 patients, both MR images and histology revealed the presence of tumor in the bone marrow compartment, usually as an extension of the intracortical tumor component (Figs. 1A, 1B, 1C, 1D, 1E, 1F and 2A, 2B, 2C, 2D). In one patient, there were no signs of bone marrow involvement based on the MR images, whereas discrete extension to the bone marrow compartment was shown on microscopy. In one other patient, no histopathologic macrosection of the specimen was available; thus, histologic examination could not reliably be assessed regarding this topic, although the MR images did not show bone marrow involvement. Regarding the histologic subtype, bone marrow extension was seen in four (67%) of six patients with classic adamantinoma and in nine (56%) of 16 patients with osteofibrous dysplasia-like adamantinoma.
Soft-tissue extension.—In only two (9%) of 22 patients, tumor extension into the soft tissues was seen (Fig. 1A, 1B, 1C, 1D, 1E, 1F). In the remaining 20 patients (91%), the tumor was limited to the cortical bone and the bone marrow compartment.
MRI macromorphology and multicentricity.—Sixteen (73%) of 22 patients had only one tumor focus within the long bone (Fig. 4A, 4B, 4C, 4D). Separated tumor foci, defined as foci of high signal intensity on either T2-weighted images or T1-weighted contrast-enhanced images, interspersed with normal-appearing cortical or spongious bone were seen in the remaining six patients (Figs. 2A, 2B, 2C, 2D and 3). The latter were three (of six) patients with classic and three (of 16) patients with osteofibrous dysplasia-like adamantinoma.
MRI micromorphology.—In 10 (45%) of 22 patients, a pattern of multiple small nodules in one or more foci was seen (Figs. 1A, 1B, 1C, 1D, 1E, 1F and 3). A lobulated pattern of a solitary focus was found in (41%) of 22 patients (Figs. 2A, 2B, 2C, 2D and 4A, 4B, 4C, 4D), and a mixed pattern, in the remaining three patients (14%). No relationship was found between MRI morphology and histologic subtype.
Signal-intensity characteristics.—All lesions showed intermediate signal intensity on T1-weighted images (equal to muscle) that was usually homogeneous. On T2-weighted images, signal intensity was always high (equal to that of fat in examinations without fat suppression). The signal was homogeneous in 13 (62%) of the 21 patients with images available and heterogeneous in the other eight patients.
Static enhancement.—Static contrast-enhanced spin-echo T1-weighted images were available in 19 patients, with fat-selective presaturation in 15 patients. Enhancement was always intense and homogeneous. There was no relationship between enhancement pattern and histologic subtype.
Dynamic enhancement.—Dynamic sequences during and after contrast administration with a high temporal resolution were performed in 14 of 22 patients. In four (29%) of 14 patients, enhancement started more than 6 sec after the earliest arterial enhancement. In most of the remaining patients (10/14, 71%), the earliest lesional enhancement was seen within 0–6 sec after arterial enhancement. In the latter 10 patients, rapidly progressive enhancement with an early plateau phase or washout, as reflected by the signal intensity–time curve, was seen. Imaging of the remaining patients revealed a more gradual increase of signal intensity during the dynamic sequence. No relationship existed between the dynamic enhancement pattern and histologic subtype.
Radiography
In this series of radiographs comprising imaging of osteofibrous
dysplasia-like and classic adamantinomas, the most common radiographic
features encountered were eccentric intracortical localization in the tibia
diaphysis, a geographic pattern of bony destruction and regular cortical
destruction, and a mixed pattern of osteolysis with ossification or septation
(Fig. 5 and
Table 2).
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Radiographs showed multifocal lesions in two patients. One satellite lesion in the bone marrow of the epiphysis, shown on MR images, could not be depicted on radiographs.
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In the present retrospective study, the results of MRI studies, including static and dynamic contrast enhancement analysis, performed before surgery in 22 patients with histologically proven adamantinoma are reported.
The intention to distinguish osteofibrous dysplasia-like adamantinoma from classic adamantinoma on the basis of MRI features was one of the goals of this study because the subtypes may have different clinical behaviors [6]. However, neither signal intensity characteristics nor static or dynamic enhancement features contributed to this differentiation.
Some consistent morphologic features, in addition to radiographic features, may lead to a likely diagnosis of either classic or osteofibrous dysplasia-like adamantinoma. All tumors were primarily localized in the tibia diaphysis (including tumors in one patient with additional lesions in the fibula), most frequently in the anterior cortical bone. There was, however, discrete or more pronounced extension toward the bone marrow in 60% of patients, as opposed to 40% of patients with tumor localization in the cortical bone only. MRI revealed optimal correlation with corresponding histologic sections regarding cortical involvement and breakthrough in 86% of patients and regarding bone marrow extension in 91%.
Two main morphologic tumor patterns were distinguished on MRI: a solitary lobulated focus (in 41% of patients) versus a pattern of multiple small nodules in one or more foci (in 45%). Separated tumor foci, defined as foci of high signal intensity on either T2-weighted or T1-weighted contrast-enhanced images, interspersed with normal-appearing cortical or spongious bone were seen in six (27%) of 22 patients. Although the number is small, this multicentric appearance occurred in three of six patients with classic adamantinoma versus only 18% of the patients with osteofibrous dysplasia-like adamantinoma.
This emphasizes the role of MRI for locoregional staging of adamantinoma. Optimal multidirectional imaging of the entire tumor-bearing bone is pivotal, particularly when reconstructive surgery with auto- or allograft transplantation is planned. Because of the preferential manifestation of adamantinoma in the anterior cortical bone of the tibia, sagittal images of the entire lower leg are usually optimal to show the exact cranial–caudal tumor extension and to identify small distant foci within the cortical bone or bone marrow compartment that can be missed on radiographs. Because all small nodules or lobulated tumor areas showed intense static enhancement, contrast-enhanced spin-echo T1-weighted images with fat-selective presaturation images were especially suitable. Ideally, a complete 3D data set is preferable to deal with multiple foci of different sizes and at different sites within the bone. Software is now available that allows the performance of reconstructions based on 3D volume data sets or even on 2D sets with interslice gaps. In regard to reconstructive surgery, axial images, either T1- or T2-weighted, are particularly useful to assess the status of the posterior cortical bone.
The intense enhancement on static contrast-enhanced T1-weighted images, which was seen on images in all patients evaluated with contrast medium, suggests high vascularity of the stroma. This has indeed been encountered when applying immunohistochemistry with vascular markers. The patterns of dynamic enhancement did not correspond with the histologic subtype of adamantinoma. There was also no association between the dynamic enhancement features and a more or less aggressive growth pattern of the osteofibrous dysplasia-like adamantinoma.
Probably the amount of capillary vessels and the density of the osteofibrous stroma in osteofibrous dysplasia-like and classic adamantinoma are responsible for the different types of enhancement curves seen in the study population. A high number of vessels may result in a rapidly progressive early enhancement, as opposed to a more gradual increase in signal intensity if a smaller number of capillary vessels are present. The presence of a loose vascularized osteofibrous stroma may result in a continuous increase in signal intensity during the second phase of the dynamic sequence, whereas a more dense stroma corresponding to a tighter interstitial space, may affect the plateau level of the signal intensity–time curve.
A hallmark of adamantinoma is its zonal architecture. The typical histopathologic feature of classic adamantinoma is the presence of abundant epithelium within the center, which gradually disappears toward the periphery of the lesion. Thus, at the periphery, the classic adamantinoma may mimic an osteofibrous dysplasia-like adamantinoma, in which the osteofibrous component predominates and isolated small groups or individual keratin-positive cells are scarcely encountered. On the other hand, individual epithelial cells may be completely absent at the periphery; this feature results in the appearance of osteofibrous dysplasia or predominantly reactive osseous tissue. Biopsy samples from these ossified peripheral parts may thus result in the wrong final diagnosis and probably surgical undertreatment. Osteofibrous dysplasia should at least be followed up thoroughly by clinical and radiologic examinations. Clinical or radiographic evidence of growth warrants a repeat biopsy.
Although some authors advocate a similar wait-and-see approach for osteofibrous dysplasia-like adamantinoma (which behaves less aggressively than classic adamantinoma), the most appropriate treatment for both histologic subtypes of adamantinoma is considered to be an en bloc resection of the tumor. Biopsies taken from the central part of the tumor, represented by the strongly enhancing foci on T1-weighted images and high signal intensity on T2-weighted images, thus seem to be optimal. This advantage emphasizes the role of MRI before diagnostic surgery. Another entity frequently included in the differential diagnosis of adamantinoma is fibrous dysplasia. Fibrous dysplasia is in general an intramedullary lesion, with a typical ground-glass pattern of bony destruction on radiographs [8]. Fibrous dysplasia may be treated conservatively, whereas intralesional surgery by curettage is allowed. In contrast, this treatment is absolutely prohibited in adamantinoma because of the high risk of recurrence and potential to metastasize [6].
In conclusion, some uniform MRI characteristics, in addition to those of radiography, may contribute to the diagnosis of adamantinoma; however, these are independent of the histologic subtype, either osteofibrous dysplasia-like or classic. A multicentric appearance seems to occur more frequently in classic adamantinoma. Furthermore, in contrast to a popular opinion that adamantinoma is a purely intracortical tumor, we found extension toward the bone marrow compartment in 60% of patients. MRI is pivotal for precise locoregional staging, especially for depiction of distant cortical foci, soft-tissue extension, and intramedullary extension and, as such, for determination of tumor-free margins and strategy for reconstructive surgery.
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