CME/SAM. Differential Diagnostic Value of Blue Reticulated Chondroid-Like Material in Aneurysmal Bone Cysts

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1 AJCP / Original Article Differential Diagnostic Value of Blue Reticulated Chondroid-Like Material in Aneurysmal Bone Cysts A Classic Histopathologic Analysis of 215 Cases Won-Jong Bahk, MD, 1 and Joseph M. Mirra, MD 2 From the 1 Department of Orthopaedic Surgery, Uijeongbu St Mary s Hospital, The Catholic University of Korea, Seoul; and 2 Orthopaedic Hospital, Los Angeles, CA. Key Words: Aneurysmal bone cyst; Telangiectatic osteosarcoma; Blue reticulated chondroid-like material Am J Clin Pathol June 2015;143: CME/SAM ABSTRACT Objectives: Our classic histopathologic study of aneurysmal bone cyst (ABC) revealed that blue reticulated chondroidlike material (BRC) is characteristic of ABC. Methods: The light microscopic findings were retrospectively analyzed in 215 cases of ABC, including 101 primary and 114 secondary cases. In addition, 22 cases of telangiectatic osteosarcoma (TOS) were drawn from the same source and used as a control. Results: We found the presence of typical BRC in 24 (23.8%) of 101 cases of primary ABC and in six (5.3%) of 114 cases of secondary ABC, with an overall incidence of 30 (14%). None of the cases of TOS showed BRC. BRC was significantly more common in primary ABC than in secondary ABC (P <.05) and in patients 19 years or younger than in those 20 years or older (P <.05). Conclusions: BRC appears to be a unique histopathologic feature of ABC, making it valuable to differentiate benign ABC from TOS. Simple H&E stain can be economically performed anywhere. Upon completion of this activity you will be able to: compare the pathologic and clinical features of primary and secondary aneurysmal bone cysts (ABCs). list the differential diagnosis of conditions that can mimic ABCs on radiography or on histologic sections. describe the histopathologic features that can differentiate ABC from telangiectatic osteosarcoma. The ASCP is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASCP designates this journal-based CME activity for a maximum of 1 AMA PRA Category 1 Credit per article. Physicians should claim only the credit commensurate with the extent of their participation in the activity. This activity qualifies as an American Board of Pathology Maintenance of Certification Part II Self-Assessment Module. The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose. Questions appear on p 906. Exam is located at Aneurysmal bone cyst (ABC) may be divided into primary, de novo ABC without a definite precursor lesion and secondary ABC with various preexisting diseases. Although the locally disturbed blood circulation within affected bone has been widely accepted as pathogenesis, 1 the exact mechanism of primary ABC still has not been clarified. It also has been undetermined if primary and secondary ABCs are developed by the same mechanism. Using a cytogenetic method, Oliveira et al 2 showed that primary and secondary ABCs have a different pathogenesis by noting the presence of neoplastic cells only in the former. They concluded that secondary ABC would likely represent a common end point of differentiation in non-abc bone tumors. Recent cytogenetic studies suggested that at least some primary ABCs are true neoplasms and not reactive tumor-simulating lesions. 3-8 Although ABC is benign in nature, it might be locally destructive, with a high propensity for recurrence after curettage. 9,10 Radiography typically shows an eccentric osteolytic Am J Clin Pathol 2015;143:

2 Bahk et al / Diagnostic Value of Blue Reticulated Chondroid-Like Material lesion with expansion of the host bone. In a large series, the margin of the lesion was sharp with or without sclerosis in 86% of cases and indistinct in the rest of the cases. 11 Histologic differentiation of ABC from telangiectatic osteosarcoma (TOS) is usually not difficult because TOS always shows highly anaplastic cells with atypical mitoses. Occasionally, however, ABC may demonstrate high-grade exuberance of spindle cells, plump bizarre nuclei, and reactive immature osteoid. 12 When such pathologic changes are coupled with bizarre radiographic manifestation, ABC could be easily mistaken for TOS. Ruiter et al 13 noted a high level of mitotic activity and increased nuclear pleomorphism in 18 of 105 cases of ABC, making the differentiation from TOS difficult. They attempted to establish an objective morphologic differential basis in unusual cases of ABC and TOS by using semiautomated histophotometric techniques. In a retrospective analysis of 215 cases of ABC, we found a deep blue-purple, reticulated, chondroid-like matrix in a clump in the wall of some cases. The finding appeared to be unique for ABC, and we termed it blue reticulated chondroid-like material (BRC). In contrast, however, such a material was not found in TOS. The purpose of our study was to describe clinicopathologic profiles of BRC and its value in discriminating ABC from TOS. Materials and Methods Materials were provided by the senior author (J.M.M.). From 3,792 cases of various bone tumors, we selected 215 (5.7%) cases of pathologically proven ABC, including 101 primary ABCs and 114 secondary ABCs. The specimens obtained from incision biopsy or surgical operation were decalcified in 5% or 10% nitric acid for varying hours depending on the hardness of the specimens prior to processing and embedding in paraffin wax. Sections (5 μm) of decalcified, formalin-fixed, paraffin-embedded bone specimens were cut. The prepared sections were stained with standard H&E. The histopathologic features were reviewed by a senior bone pathologist (J.M.M.) with the main theme centered on the diagnostic usefulness of the histopathologic profiles of BRC in benign and malignant ABC. Clinical information was obtained from medical records. In addition, 22 cases of TOS were recruited from the same source for a comparative and control analysis. For the current study, we defined an osteosarcoma with secondary ABC as an osteosarcoma having benign ABC without malignant cells in its wall proper. TOS was defined as an osteosarcoma with prominent, unequivocal malignant cells in the cystic walls. We performed the c 2 test to determine the statistical significance of the differences in frequency of BRC between sexes, anatomical locations, primary and secondary ABC, and the patient s age ( 19 years or 20 years). P values less than.05 were judged to be statistically significant. This study was conducted with approval of the institutional review boards of Uijeongbu St Mary s Hospital, The Catholic University of Korea. Results Patient Data Primary Secondary Total Age (y) Figure 1 Age distribution of patients with primary and secondary aneurysmal bone cysts. Of 215 cases, 101 (47.0%) were primary ABCs without detectable underlying disease, and 114 (53.0%) were secondary ABCs with a preexisting bone lesion. The age of all patients ranged from 1 to 83 years, with a mean of 22.4 years. At the time of diagnosis, 111 (51.6%) of 215 patients were 19 years or younger Figure 1. Breakdown showed 101 primary ABCs in 40 men and 61 women with age ranging from 1 to 69 years (mean, 21.5 years). Of 101 patients with primary ABCs, 57 (56.4%) were 19 years or younger, including eight children younger than 5 years; four (4.0%) were older than 50 years; and the remainder were aged 20 to 49 years. On the other hand, 114 secondary ABCs occurred in 67 men and 47 women with age ranging from 1 to 83 years (mean, 23.5 years). Of 114 patients with secondary ABCs, 54 (47.4%) were 19 years or younger, including four children younger than 5 years, and 11 (9.6%) patients were older than 50 years. In total, there were 107 men and 108 women. Site of Involvement The involvement sites of all ABCs in descending order were the long bones (n = 128; 59.5%), the spine (n = 24; 11.2%), the pelvis (n = 16; 7.4%), the skull and facial bones (n = 14; 6.5%), the hand and foot bones (n = 13; 6.0%), the rib (n = 8; 3.7%), the scapula (n = 5; 2.3%), and other bones (n = 7; 3.3%). The affected long bones were the femur (n 824 Am J Clin Pathol 2015;143:

3 AJCP / Original Article Image 1 Light microscopy of aneurysmal bone cysts may show spotty, winding, snake-like ribbons of osteoid within walls of cyst-like lesions (black arrows). Note the incipient row of osteoblasts (arrowheads) strongly suggesting benignancy despite occasional bizarre, pleomorphic cells (H&E, 200). Image 2 Light microscopic examination of early blue reticulated chondroid-like material production shows microcalcification within spindle cells, which are in the process of degeneration and necrosis (circles), stimulating pericellular calcification (H&E, 200). = 53; 24.6%), the tibia (n = 33; 15.3%), the fibula (n = 18; 8.4%), the humerus (n = 16; 7.4%), the radius (n = 7; 3.3%), and the ulna (n = 1; 0.5%). some fields with exuberant fibroblasts showed bizarre nuclei with occasional typical mitoses. However, definite anaplasia or unequivocal atypical mitoses were never seen. Peculiar mineralized matrices were observed in a clump only within ABC walls. Initially, they were chondroidlooking pinkish material assuming microcalcification within spindle cells (myofibroblasts), which were in the process of focal prenecrotic degeneration Image 2. Such deposits gradually grew larger and became confluent. With time, the substance typically turned dark blue or purple in color and lacy or reticulated in texture Image 3. Age and sex, location and subtype of the tumor, and underlying lesions in patients having ABC with BRC are summarized in Table 1. BRC was observed in 13 (12.1%) of 107 male patients and 17 (15.7%) of 108 female patients. The difference was statistically not significant (P >.05). BRC was present in 24 (23.8%) of 101 cases of primary ABC but in only six (5.3%) of 114 cases of secondary ABC, with the overall incidence being 30 (14.0%) of 215 cases. The difference in incidence was statistically significant (P <.001). Underlying tumor in secondary ABC with BRC included giant cell tumor (n = 3), chondroblastoma (n = 2), and low-grade osteosarcoma (n = 1). In primary ABC, BRC was found in 18 (31.6%) of 57 patients 19 years or younger and in six (13.6%) of 44 patients 20 years or older. In secondary ABC, BRC was found in six (11.1%) of 54 patients 19 years or younger and in none of 57 patients 20 years or older. Eighteen (75.0%) of 24 cases of primary ABC with BRC and all six (100%) cases Preexisting Lesions in Secondary ABC The preexisting lesions in 114 cases of secondary ABC included both various benign conditions and malignant tumors: giant cell tumor (n = 39; 18.1%); chondroblastoma (n = 23; 10.7%); fibrous dysplasia (n = 17; 7.9%); osteosarcoma (n = 9; 4.2%), including one postirradiation, two highgrade, four low-grade, and two periosteal cases; nonossifying fibroma (n = 7; 3.3%); osteoblastoma and simple bone cyst (n = 3 cases each); Ewing sarcoma, giant cell reparative granuloma, chondrosarcoma, and hyperparathyroidism (n = 2 cases each); and osteoid osteoma, ossifying fibroma, eosinophilic granuloma, chondromyxoid fibroma, and fracture (n = 1 case each). Pathologic Features The constant features of conventional ABC included the presence of multilocular cyst-like walls composed of bland fibroblasts with or without blood within. The degree of fibroblastic cellularity was variable, and some cases showed fairly exuberant fibroblasts. The stroma of the thin wall was composed of bland scar-like tissue having a characteristic spotty, winding, and snake-like ribbon of osteoid with osteoblastic rimming in association with occasional benign giant cells Image 1. High-power microscopic examination of Am J Clin Pathol 2015;143:

4 Bahk et al / Diagnostic Value of Blue Reticulated Chondroid-Like Material Image 3 Light microscopy shows microcalcific deposits to have become larger and confluent. This peculiar substance is dark blue or purple in color and reticulated in texture (arrows) (H&E, 100). with secondary ABC with BRC occurred in patients 19 years or younger. The overall difference between patients 19 years or younger and those 20 years or older was statistically significant (P <.05). The BRC incidence in primary ABC was five (33.3%) of 15 cases in the spine, 14 (25.9%) of 54 cases in the long bones, four (25.0%) of 16 cases in the skull and flat bones, and one (25.0%) of four cases in the metacarpal bones. The incidence in secondary ABC was one (20.0%) of five cases in the rib, one (11.1%) of nine cases in the spine, one (11.1%) of nine cases in the metacarpal bones, and three (4.1%) of 74 cases in the long bones. In total, BRC was found in the spine (25.0%), the skull and flat bones (21.1%), the metacarpal bones (15.4%), and the long bones (13.3%), in descending order. Location-wise, there were no statistically significant differences (P >.05). In contrast, BRC was never seen in TOS. Extensive necrosis was observed in one case of ABC, whereas 14 (63.6%) of 22 cases of TOS showed extensive necrosis focally or diffusely. Twenty-five (11.7%) cases showed spotty opacities within the mass, representing intramural BRC or calcification on radiograph and/ or computed tomography (CT) scan Image 4. Discussion Recent cytogenetic studies suggested that primary ABC is a true neoplasm rather than a simple reactive process to vascular disturbance. Panoutsakopoulos et al7 demonstrated that chromosomal translocation t(16;17) (q22;p13) was a recurrent cytogenetic abnormality in primary ABC. Sciot et 826 Am J Clin Pathol 2015;143: al8 described chromosomal aberrations in ABC. Oliveira et al2 identified neoplastic cells by exhibiting USP6 or CDH11 rearrangements in 36 (69%) of 52 primary ABCs but not in 17 cases of secondary ABC. In our series of 215 cases, 114 (53.0%) ABCs were secondary in nature and associated with both benign and malignant lesions. This incidence of ours is higher than those of previous reports,1,14 probably due to the referral nature of our material. Common associated lesions included giant cell tumor, chondroblastoma, and fibrous dysplasia, occupying 79 (69.3%) of 114 cases of secondary ABC. Interestingly, fracture was associated in one case. Thirteen (6.0%) cases in our series were related to malignant tumors, including osteosarcoma, chondrosarcoma, and Ewing sarcoma. Approximately half of secondary ABCs (52 of 114 cases; 45.6%) were linked with locally aggressive giant cell tumor (39 cases) and sarcomas (13 cases). Clinically, the critical diagnostic point is to separate evolving ABC from TOS as promptly as possible. Although histologic discrimination is usually not hard, diagnosis may become difficult when the specimen is inadequate.15 ABC and TOS can be mistaken for each other because clinical, radiologic, and histologic findings overlap.15,16 Therefore, biopsy samples are to be extensive enough and include solid parts of the lesion to exclude associated conditions. Some authors stressed that both entities could be differentiated only by evaluating nuclear details such as hyperchromasia, pleomorphism, and mitotic activity.17,18 The diagnosis of ABC in cases with reactive immature osteoid with atypical plump cells must be made carefully with skepticism and scrutiny.10,12 Kahn et al19 described two cases in which an ABC was erroneously overdiagnosed as osteosarcoma. On the other hand, three of 25 cases of TOS in a Mayo Clinic study were diagnosed elsewhere as ABC.20 A cytogenetic study might be called for as an ancillary diagnostic tool to avoid misdiagnosis, but the study is expensive and still not widely available. ABC is known to show diploid DNA contents, and TOS shows complex karyotypes and numerous gains and losses More recently, a cytogenetic study was undertaken for the confirmative diagnosis of ABC in which extraordinary lung metastasis occurred. The researchers could exclude secondary ABC associated with primary bone sarcoma, malignant change of ABC, and TOS by detecting the USP6 gene with florescence in situ hybridization.24 Microscopically, a constant feature was the presence of multiloculated cyst-like walls with a varying degree of fibroblastic cells, multinuclear giant cells, and osteoid within the walls. The osteoid was typically a spotty and ribbon-like sliver. On occasion, cytologic findings such as hypercellularity, cell plumpness with bizarre nuclei, and some mitoses in association with osteoid imparted a sarcomatoid aura

5 AJCP / Original Article Table 1 Age, Sex, Location, Subtype, and Underlying Lesions in Patients With ABCs Associated With Blue Reticulated Chondroid-Like Material Patient No. Age, y Sex Location Subtype of ABC Underlying Lesion 1 8 F Lumbar spine Primary 2 19 F Thoracic spine Primary 3 11 F Fibula Primary 4 6 F Femur Primary 5 11 M Femur Primary 6 15 F Tibia Primary 7 10 F Occiput Primary 8 20 M Femur Primary 9 13 M Scapula Primary M Lumbar spine Primary 11 1 F Humerus Primary 12 7 M Metatarsus Primary M Humerus Primary F Thoracic spine Primary 15 2 M Radius primary Primary F Thoracic spine Primary F Humerus Primary 18 9 M Tibia Primary M Humerus Primary F Femur Primary 21 5 F Tibia Primary 22 7 F Scapula Primary F Femur Primary M Parietal bone Primary F Rib Secondary Chondroblastoma M Tibia Secondary Chondroblastoma 27 5 M Metatarsal Secondary Giant cell tumor 28 7 M Fibula Secondary Giant cell tumor F Lumbar spine Secondary Giant cell tumor F Tibia Secondary Low-grade osteosarcoma ABC, aneurysmal bone cyst. that could be mistaken for TOS. In some of our cases, a peculiar mineralized matrix was noted within or adjacent to osteoid in the ABC component. However, it was not discovered in the underlying tumor component. This unusual mineralized matrix has been mentioned earlier by some authors, but no detailed documentation in terms of incidence, histologic features, and diagnostic significance for ABC has been published. Tillman et al 18 briefly described small, irregularly dispersed foci with a chondroid aura that were considered part of the reparative reaction. Dahlin 25 also mentioned that some cases had a chondroid aura, which is unusual in other bony lesions. Mirra 26 observed a peculiar, distinctly blue, lattice-like, primitive matrix that was thought to be chondroid. The chondroid matrix was believed to be strongly suggestive, if not pathognomic, of repair tissue in ABC. Sanerkin et al 27 observed foci of degenerate calcifying fibromyxoid tissue in a solid variant of ABC that was equivalent to the foci with the chondroid aura described by Tillman et al. 18 Years later, the material was described as a calcified matrix with a chondroid aura, and it was thought to be the most unusual finding of an ABC by the Mayo Clinic group. 10 They observed the aura in 35% of 238 cases and found it in flat bones, spines, cranium and facial bones, and long bones, in descending order. We prefer to name this peculiar matrix as BRC because it is typically deep blue in color and cartilage-like and reticulated in appearance. BRC is mostly multifocal and diffuse in distribution and easy to see. According to our observations, it is a cartilage-like material, initially pinkish in color, with microcalcification within or around spindle cells. The matrix gradually grows larger, becoming confluent. It interferes with the nutrition of myofibroblasts, leading to micronecrosis of intervening cells, eventually changing the color to blue due to lacy, clumpy calcifications. BRC is usually found within or adjacent to osteoid or woven bone trabeculae and typically is oriented in triangles. The structure is lattice-like, and the cells within it are flattened to ovoid and amorphous in appearance. Although BRC is not common, it is thought to be highly characteristic for ABC. BRC is observed four times more often in primary ABC than in secondary ABC, but it has never been found in TOS. A lower incidence in secondary ABC might be related to the smaller extent of the ABC component that is focally present throughout the main lesion. The Am J Clin Pathol 2015;143:

6 Bahk et al / Diagnostic Value of Blue Reticulated Chondroid-Like Material In conclusion, BRC is a unique feature in both primary and secondary ABCs and is a useful parameter to differentiate ABC from TOS. BRC was much more frequently seen in primary ABC than in secondary ABC and in patients 19 years or younger than in those 20 years or older. The difference was statistically significant. This method is economical and can be done anywhere. Address reprint requests to Dr Bahk: Dept of Orthopaedic Surgery, Uijeongbu St Mary s Hospital, The Catholic University of Korea, 65-1 Geumohdong, Uijeongbu, Gyunggido, Korea; wjbahk@catholic.ac.kr. Image 4 Computed tomography scan shows a large, expansile lesion involving the scapula with intralesional geographic opacities (arrow). The opacities represent a large amount of intramural blue reticulated chondroid-like material. frequency of BRC in primary ABC in the present series (23.8%) was lower than that of the Mayo Clinic s series (35%). 10 The difference was probably due to the fact that most cases were referred from outside with more or less limited tissue sampling or a restricted number of slides. BRC was far more common in patients 19 years or younger than in those 20 years or older. Actually, 24 of 30 cases with BRC (80%) were found in the younger group. It is of interest to note that while only 25% of ABCs occurred in the spine or flat bones, 50% of ABCs with BRC were seen in those bones. The incidence was statistically insignificant. Two cases of BRC were difficult to diagnose as ABC. However, we considered that BRC was useful to screen and differentiate ABC from TOS in such rare cases with the H&E stain alone. In the future, it can be confirmed by molecular work when necessary. Alers et al 28 stressed that EDTA is highly preferable to routinely used acid decalcifier for DNA in situ hybridization and comparative genomic hybridization. More recently, Puls et al 29 suggested that strong acids such as hydrochloric acid and nitric acid severely damage DNA and RNA, rendering such treated tissue useless for molecular pathologic analyses. Thus, they moved to use EDTA as a better decalcifier for molecular pathology. It would appear that nitric acid is to be replaced by EDTA for future molecular works. Around 20% of the cases have been reported to show spotty opacities within the mass on a radiograph and/or CT scan representing intramural BRC. 30 In our series, 25 (11.6%) cases showed such spotty opacities within the mass on radiograph and/or CT scan. References 1. Biesecker JL, Marcove RC, Huvos AG, et al. Aneurysmal bone cysts: a clinicopathologic study of 66 cases. Cancer. 1970;26: Oliveira AM, Perez-Atayde AR, Inwards CY, et al. USP6 and CDH11 oncogenes identify the neoplastic cell in primary aneurysmal bone cysts and are absent in so-called secondary aneurysmal bone cysts. Am J Pathol. 2004;165: Baruffi MR, Neto JB, Barbieri CH, et al. Aneurysmal bone cyst with chromosomal changes involving 7q and 16p. Cancer Genet Cytogenet. 2001;129: Herens C, Thiry A, Dresse MF, et al. Translocation (16;17) (q22;p13) is a recurrent anomaly of aneurysmal bone cysts. Cancer Genet Cytogenet. 2001;127: Leithner A, Lang S, Windhager R, et al. Expression of insulin-like growth factor-i (IGF-I) in aneurysmal bone cyst. Mod Pathol. 2001;14: Leithner A, Machacek F, Haas OA, et al. Aneurysmal bone cyst: a hereditary disease? J Pediatr Orthop. 2004;13: Panoutsakopoulos G, Pandis N, Kyriazoglou I, et al. Recurrent t(16;17)(q22;p13) in aneurysmal bone cysts. Genes Chromosomes Cancer. 1999;26: Sciot R, Dorfman H, Brys P, et al. Cytogenetic-morphologic correlations in aneurysmal bone cyst, giant cell tumor of bone and combined lesions: a report from the CHAMP study group. Mod Pathol. 2000;13: Mankin HJ, Hornicek FJ, Villafuerte EJ, et al. Aneurysmal bone cyst: a review of 150 patients. J Clin Oncol. 2005;23: Vergel De Dios AM, Bond JR, Shives TC, et al. Aneurysmal bone cyst: a clinicopathologic study of 238 cases. Cancer. 1992;69: Kransdorf MJ, Sweet DE. Aneurysmal bone cyst: concept, controversy, clinical presentation, and imaging. AJR Am J Roentgenol. 1995;164: Mirra JM. Aneurysmal bone cyst. In: Mirra JM, ed. Bone Tumors: Clinical, Radiologic and Pathologic Correlations. Philadelphia, PA: Lea and Febiger; 1989: Ruiter DJ, Cornelisse CJ, Rijssel TG, et al. Aneurysmal bone cyst and telangiectatic osteosarcoma: a histopathological and morphometric study. Virchows Arch. 1977;373: Martinez V, Sisson HA. Aneurysmal bone cyst: a review of 123 cases including primary lesions and those secondary to other bone pathology. Cancer. 1988;61: Am J Clin Pathol 2015;143:

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