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Wangaryattawanich, et al.: Imaging features of cartilaginous tumors of the head and neckotherwise maintained. MRI appearance of chondromas isless specific because of its relative insensitivity in detectingchondroid calcifications. It can, however, provide additionalinformation with regards to the extent of the lesion due toits high soft tissue contrast resolution.[21] Chondromas andchondrosarcomas are difficult to distinguish on the basis ofimaging, and as such histopathology is always required forconfirming the diagnosis.[21,22]ChondroblastomabacFigure 2: Characteristic CT and MRI features of well-differentiatedcartilaginous tumors. A 19-year-old man with sinonasalchondrosarcoma presenting with sinonasal obstructive symptoms.Axial maxillofacial CT image in bone window (a) shows a largeright sinonasal mass containing internal ring-and-arc calcifications,a classic feature of calcified chondroid matrix (arrow). The tumoris heterogeneously hyperintense on T2W MRI image (b) andmoderately enhancing on post-contrast T1W MRI image withfat suppression (c). Note the T2 hypointense area in the posterioraspect of the tumor (arrowhead in b) corresponding to the area ofdense calcification on CT.Chondroblastomas are rare benign but locally aggressivebone tumors which commonly involve the epiphysis of thelong bones such as distal femur, proximal tibia, and proximalhumerus. Craniofacial chondroblastomas are uncommon,accounting for 2–7% of all chondroblastomas.[1,23,24] Themost common location in the head and neck region is theskull base, with a predilection for the squamous portionof the temporal bone adjacent to the temporomandibularjoint. The other less common sites include mandibularcondyle [Figure 4], paranasal sinuses, and maxilla.[25-28]Histopathological features of chondroblastomas includepolygonal mononuclear cells (chondroblasts), multinucleatedgiant cells, and chondroid matrix. A fine network ofpericellular calcification (so called “chicken-wire” pattern)can be seen in varying amounts. Clinical manifestationsdepend on tumor location, for example, with skull basechondroblastomas presenting as cranial neuropathy andchondroblastoma of the TMJ presenting with jaw pain, etc.Radiologically, chondroblastomas are seen as nonspecificwell-defined expansile osseous lesions containing a variableamount of internal chondroid calcification. Invasion of thesurrounding structures indicates the locally aggressive natureof these lesions.[29,30] Intratumoral cystic degeneration orsecondary aneurysmal bone cysts occur frequently in up toone third of these tumors.[1,23] Although the tumors are locallyaggressive, distant metastasis is rare. Surgical resection withcomplete tumor removal is the standard treatment.[31]Chondromyxoid fibromaabFigure 3: Laryngeal chondroma. A 51-year-old woman withlaryngeal chondroma presenting with hoarseness for 6 months.Axial contrast-enhanced (a) and coronal-reformatted (b) CT imagesshow a small expansile hypodense lesion at the left lamina of thethyroid cartilage (arrows). She underwent open resection of thelesion. Histopathology revealed a hypocellular tumor containinghyaline cartilage. The overlying perichondrium was intact with noevidence of destructive growth.Journal of Clinical Imaging Science 2021 11(66) 4CMF account for less than 1% of all primary osseoustumors and predominantly affect the metaphysis of the longbones, particularly in the lower extremities. CMF of theskull and facial bones are exceedingly rare, with less than100 cases reported in English literature.[32] The previouslyreported locations of craniofacial CMF are skull base,sinonasal cavity, and, less frequently, the calvarium.[31,32]These tumors demonstrate slow growth and tend to invadesurrounding bones and soft tissue structures. Radiologicfindings of CMF are nonspecific. On CT, CMFs are wellcircumscribed, expansile osseous lesions with a sclerotic

Wangaryattawanich, et al.: Imaging features of cartilaginous tumors of the head and neckbacabcFigure 4: Chondroblastoma. A 36-year-old woman withchondroblastoma arising from the right mandibular condylepresenting with worsening right jaw pain. Axial T2WI MRI image(a), axial (b) and coronal (c) contrast-enhanced T1W MRI imageswith fat suppression show an exophytic enhancing T2 hyperintensemass arising from the right mandibular condyle projectingmedially into the right masticator space (arrows). Note edema andenhancement of the right lateral pterygoid muscle (arrow heads).Figure 5: Chondromyxoid fibroma. A 56-year-old woman withchondromyxoid fibroma of the right central skull base presentingwith multiple right cranial neuropathy. Axial T1WI (a), axialT2WI (b) and coronal contrast-enhanced T1W MRI image with fatsuppression (c) show a large expansile mass arising from the rightgreater wing of sphenoid (arrows). The tumor demonstrates mixedsignal intensity on both T1WI and T2WI with small lobular foci ofT2 hyperintensity, and diffuse contrast enhancement.rim. Intralesional calcification is an uncommon imagingfeature and can be identified in approximately 10% of allCMF.[33] MRI characteristics of CMF are similar to othercartilaginous tumors which show low signal on T1WI andheterogenous high signal on T2WI due to its cartilaginousand myxoid components, and heterogeneous enhancementon postcontrast sequence [Figure 5]. The nonspecificimaging appearance spurs a wide differential diagnosis whichincludes chondrosarcoma, chordoma, chondroblastoma,and chondroblastic osteosarcoma. Total tumor resection isthe treatment of choice, with curative intention. In general,curettage is not recommended due to its higher recurrentrate (up to 25%). The role and efficacy of radiation therapyfor local tumor control remains controversial.[32]elsewhere in the body and are seen as exophytic osseouslesions with continuity of bone marrow from the parent boneinto the tumor [Figure 6]. A layer of cartilage known as thecartilaginous cap is seen at the growing end of the lesion.The cartilaginous cap is better seen on MR and typicallyhas low signal on T1WI and high signal on T2WI.[36] Onpostcontrast images, there is enhancement at the peripheryof the lesion which correlates on histology with fibrovasculartissue covering the nonenhancing cartilaginous cap.[39] Thecartilaginous portion of osteochondroma may undergomalignant transformation. Abnormal thickening of thecartilaginous cap (exceeding 1.5–2.5 cm) on imaging is anominous sign and is viewed with suspicion for malignantdegeneration [Figure 7].[40]OsteochondromaSynovial chondromatosisOsteochondroma is a common benign bone lesion whichusually occurs at the end of long bones such as distalfemur.[34] Osteochondroma in the head and neck region isrelatively rare. The most common location is the mandible,particularly the mandibular condyle and coronoid process,but it can arise from any part of the mandible or other osseousstructures in the head and neck.[34-38] On imaging, head andneck osteochondromas are similar to osteochondromas seenSynovial chondromatosis is a benign but locally aggressivedisease characterized by chondroid metaplasia of thesynovium, with subsequent formation of intra-articular loosebodies, causing destruction of the joint.[41,42] In the head andneck, it frequently involves the temporomandibular joint.Synovial chondromatosis can be divided into two subtypes– primary and secondary.[41,42] Pathogenesis of primaryform remains unknown, but according to recent cytogeneticJournal of Clinical Imaging Science 2021 11(66) 5

Wangaryattawanich, et al.: Imaging features of cartilaginous tumors of the head and neckaabFigure 6: Osteochondroma. A 28-year-old woman withosteochondroma of the right mandibular condyle presentingwith chronic right jaw pain. Axial (a) and coronal-reformatted(b) CT images in bone window show an exophytic osseous lesionoriginating from the right mandibular condyle, continuous with themedullary cavity of the mandible (arrow). Note remodeling of theskull base from chronic long-standing pressure effect (arrowhead).abFigure 7: Osteochondroma with secondary chondrosarcoma.A 70-year-old man with secondary chondrosarcoma originatingfrom the osteochondroma of the cervical spine presenting withpalpable lump in the neck. Axial T2W MRI image (a) shows anexophytic T2 hyperintense mass arising from the right ventral aspectof C4 vertebral body (arrow). Axial CT image in bone window (b)shows a few small calcific foci within the tumor (arrowhead). Note asmall underlying osteochondroma deep to the tumor (black arrow).studies, it is believed to be a benign neoplastic process ratherthan metaplastic disease.[43] In contrast, secondary form isassociated with underlying joint diseases such as mechanicaljoint abnormalities or arthritic conditions. Malignanttransformation of primary synovial chondromatosis tochondrosarcoma may occur although it is uncommon.[44]Radiologic features of synovial chondromatosis includejoint effusion, abnormal synovial thickening andenhancement suggestive of synovitis, adjacent bone erosiondue to mechanical pressure, and calcified or noncalcifiedintra-articular loose bodies [Figure 8].[41,42] In chronicdisease, there may be imaging features of coexistentsecondary osteoarthritis and asymmetric joint spacenarrowing. There is potential for intracranial tumorextension due to its close proximity to skull base. CT isthe best imaging modality for detecting calcified intraarticular loose bodies and for assessment of bone erosion.Journal of Clinical Imaging Science 2021 11(66) 6bFigure 8: Synovial chondromatosis. A 45-year-old woman withsynovial chondromatosis initially presenting with chronic nasalcongestion. The left temporomandibular joint abnormality wasincidentally found on maxillofacial CT. Coronal-reformatted CTimage in bone window (a) and coronal contrast enhanced T1WMRI image with fat suppression (b) show abnormal synovialthickening and enhancement with extensive bone erosion of theleft mandibular condyle and adjacent skull base (arrows). Noteabnormal widening of the left temporomandibular joint.MRI can provide additional information on soft tissueabnormalities, including synovitis, and bone marrowinvolvement. On MRI, the signal characteristics of intraarticular loose bodies are variable depending on the degreeof mineralization. Noncalcified loose bodies typically havelow-to-intermediate signal on T1WI and high signal onT2WI whereas calcified loose bodies show fat signal witha peripheral hypointense rim on T1WI and low signal onT2WI [Figure 9].[41] During the early course of the disease,it can be difficult to diagnose synovial chondromatosis onMRI because loose bodies are not well formed, or they maybe obscured by joint effusion.[45]Chondromesenchymal hamartomaChondromesenchymal hamartoma is a rare benign, slowgrowing, locally destructive, tumor-like lesion that containsmixed proliferating mesenchymal and cartilaginouselements such as mature and immature hyaline cartilage.This rare tumor-like lesion occurs predominantly ininfants and young children. The most common sites aresinonasal cavity and orbit.[46,47] The mass can invade skullbase and extend intracranially.[48] There is an associationof pathologic DICER1 genetic variants, a hereditary cancerpredisposition syndrome, with nasal chondromesenchymalhamartoma.[49,50] As such, otolaryngologic evaluation shouldbe performed in individuals with pathogenic DICER1genetic variants who have persistent nasal obstruction.[49]Surgical resection is the treatment of choice.[48] On imaging,chondromesenchymal hamartomas are seen as expansileheterogeneous mixed solid and cystic masses [Figure 10].Approximately, 50% of nasal chondromesenchymalhamartomas contain internal calcifications. On MRI,tumors typically have low-to-intermediate signal on T1,heterogeneous hyperintense signal on T2, and markedheterogeneous contrast enhancement.[51,52]

Wangaryattawanich, et al.: Imaging features of cartilaginous tumors of the head and neckmultiple enchondromas.[54,57] The standard treatment forchondrosarcoma is surgical resection. Adjuvant radiationis usually given when there is residual tumor followingresection or close resection margins to improve local tumorcontrol. Chondrosarcoma is generally considered to beunresponsive to chemotherapy.[55]abFigure 9: Synovial chondromatosis with calcified intra-articularloose bodies. A 50-year-old woman with synovial chondromatosispresenting with left jaw pain. Axial CT image in bone window (a)shows several small calcified intra-articular loose bodies in the lefttemporomandibular joint (arrow) which are hypointense on axialT2W MRI image (b) (arrowhead). Note diffuse synovial thickeningand distension of the joint capsule (black arrow).abFigure 10: Chondromesenchymal hamartoma. A 16-year-oldman with DICER1 mutation and sinonasal chondromesenchymalhamartoma presenting with chronic sinonasal obstructivesymptoms. Axial (a) and coronal reformatted (b) CT images in bonewindow show polypoid opacification with scattered calcifications inbilateral ethmoid sinuses (arrows).MALIGNANT CARTILAGINOUS TUMORSChondrosarcomaChondrosarcoma is the third most common primarymalignant bone tumor after multiple myeloma andosteosarcoma.[53] Head and neck chondrosarcomas accountsfor 1–12% of all chondrosarcomas. They are usually lowgrade (WHO Grade 1 and 2) with slow growth and indolentclinical course.[54] Distant metastasis is uncommon in lowgrade tumors but is more frequent in higher grade tumors(that is, WHO Grade 3). The most common location in thehead and neck is the skull base, with approximately 60–70% of tumors emanating from the petroclival fissure.[54]The other sites such as larynx and sinonasal cavity are lessfrequent.[55,56] Chondrosarcomas usually occur in isolationbut are occasionally associated with Ollier diseaseor Mafucci syndrome, rare diseases characterized byHead and neck chondrosarcomas appear to be a distinctpathologic entity compared to chondrosarcomas arisingelsewhere in the body.[55] A meta-analysis study has shownthat head and neck chondrosarcomas tend to be lowergrade and have significantly higher 10-year disease-specificsurvival and overall survival compared to chondrosarcomasat other sites.[55] A recent study also found that the incidenceof IDH mutation is different among the head and neckchondrosarcomas of different subsites.[58] Approximately,86% of skull base chondrosarcomas have an IDH mutationwhile the incidence of IDH mutation in laryngotrachealchondrosarcomas is only 12%. More interestingly, no IDHmutations are found in maxillofacial chondrosarcomas. Theauthors hypothesized that this could be related to differenttypes of ossification (that is, enchondral ossification in theskull base compared to intramembranous ossification in themaxillofacial bones) and different pathway of tumorigenesisin each location.[58]Radiologically, chondrosarcomas are expansile soft tissuemasses with bone erosion and invasion of adjacent structures.Up to 50% of skull base chondrosarcomas show intratumoralcalcification on CT.[59] Intratumoral chondroid calcification(for example, ring-and-arc or popcorn appearance) is one ofthe most helpful imaging features suggesting cartilaginousorigin of the tumor and best depicted on CT. MRI can providemore information regarding bone marrow and soft tissueinvolvement. MR signal characteristics of chondrosarcomaare low-to-intermediate signal on T1 and hyperintensesignal on T2, with a variable degree of contrast enhancement[Figure 11].[60] Low-grade chondrosarcomas may containinternal T2 hypointense septations and septal enhancementwhich corresponds to fibrovascular tissue on histopathologywhile the nonenhancing areas within tumors represent theareas of hyaline cartilage, cystic mucoid tissue, and tumornecrosis.[39]The main differential diagnosis of skull base chondrosarcomais chordoma; it can be difficult to differentiate the two dueto overlapping imaging appearance. The tumor locationis a helpful imaging clue that may help in differentiationbetween these two entities. Skull base chondrosarcomasare more frequently located off-midline near the petrooccipital fissure, whereas chordomas are more oftenlocated in the midline of the clivus.[61] DWI MRI withquantitative assessment of apparent diffusion coefficient(ADC) values may be helpful in distinction, with somestudies demonstrating skull base chondrosarcomas haveJournal of Clinical Imaging Science 2021 11(66) 7

Wangaryattawanich, et al.: Imaging features of cartilaginous tumors of the head and neckbaabFigure 12: Laryngeal chondrosarcoma. A 59-year-old man withlaryngeal chondrosarcoma presenting with progressive hoarsenessof voice. Axial (a) and coronal-reformatted (b) contrast-enhancedCT images show an expansile partially calcified mass arising fromthe left lateral aspect of the cricoid cartilage (arrows), severelynarrowing the airway. Note characteristic chondroid matrixcalcification within the tumor.cFigure 11: Skull base chondrosarcoma. A 31-year-old man withskull base chondrosarcoma presenting with progressive left cranialneuropathy. Axial T2W MRI image (a) and coronal contrast-enhancedT1W MRI image with fat suppression (b) show a large expansileheterogeneously enhancing T2 hyperintense extraaxial mass centeredat the left petroclival fissure (arrows) extending into the prepontinecistern and causing mild mass effect on the adjacent brainstem andleft temporal lobe. The tumor contains subtle small calcifications(arrowhead), a clue to the diagnosis, best seen on CT (c).higher ADC values compared to chordomas, though furtherresearch is required.[61-63]In the larynx, chondrosarcoma is the most commonnonepithelial tumor, and it is much more common thanchondroma.[64] The most frequent sites of tumor are cricoidcartilage followed by thyroid cartilage. CT characteristics oflaryngeal chondrosarcoma is an endolaryngeal soft tissue masswith or without extralaryngeal extension.[65] Approximately,70–80% of laryn

structures in the head and neck.[34-38] On imaging, head and neck osteochondromas are similar to osteochondromas seen elsewhere in the body and are seen as exophytic osseous lesions with continuity of bone