Neuroradiology (2010) 52:1179–1184 DOI 10.1007/s00234-010-0758-6
HEAD AND NECK RADIOLOGY
Nasal polyps with metaplastic ossification: CT and MR imaging findings Yi Kyung Kim & Hyung-Jin Kim & Jinna Kim & Seung-Kyu Chung & Eunhee Kim & Young-Hyeh Ko & Sung Tae Kim
Received: 29 April 2010 / Accepted: 9 August 2010 / Published online: 18 August 2010 # Springer-Verlag 2010
Abstract Introduction Metaplastic ossification is a rare event in nasal polyps. The purpose of this study was to review the computed tomography (CT) and magnetic resonance (MR) imaging findings of nasal polyps with metaplastic ossification. Methods CT (n=5) and MR (n=3) images of five patients (four men and one woman; mean age, 59 years) with surgically proven nasal polyp with metaplastic ossification were retrospectively reviewed. The location and morphologic characteristics of metaplastic ossification were documented as well. Results All lesions were seen as lobulated (n=3), ovoid (n= 1), or dumbbell-shaped (n=1) benign-looking masses with a mean size of 3.7 cm (range, 2.4–6.5 cm), located unilaterally in the posterior nasal cavity and nasopharynx (n=2), posterior nasoethmoidal tract (n=2), and maxillary sinus and nasal cavity (n=1). Compared with the brain stem, the soft tissue Y. K. Kim : H.-J. Kim (*) : E. Kim : S. T. Kim Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-Dong, Kangnam-Ku, Seoul 135-710, South Korea e-mail:
[email protected] J. Kim Department of Radiology, Yonsei University College of Medicine, Seoul, South Korea S.-K. Chung Department of Otorhinolaryngology-Head and Neck Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea Y.-H. Ko Department of Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea
components of all lesions demonstrated isoattenuation on precontrast CT scans, slight hypointensity on T1-weighted MR images, and hyperintensity on T2-weighted MR images. On contrast-enhanced MR images, heterogeneous enhancement with marked peripheral enhancement was seen in two and homogeneous moderate enhancement in one. All lesions contained centrally located radiodense materials on CT scans, the shape of which was multiple clustered in three, single nodular in one, and single large lobulated in one. Conclusion Although rare, metaplastic ossification can occur within nasal polyps. The possibility of its diagnosis may be raised when one sees a benign-looking sinonasal mass with centrally located radiodense materials on CT scans. MR imaging may be useful when mycetoma or inverted papilloma cannot be ruled out on CT scans. Keywords Nasal polyp . Metaplastic ossification . Computed tomography . Magnetic resonance imaging
Introduction Nasal polyp is a common disease that usually follows allergy and chronic sinonasal infection [1, 2]. Sometimes, various histologic changes, such as epithelial atypia and squamous metaplasia, can occur in the respiratory epithelium covering nasal polyps [3]. Metaplastic ossification very rarely occurs within nasal polyps, which has been reported in only five cases in the English language literature [4–7]. It refers to the formation of heterotopic bone by osteoblasts [8]. Similar osseous metaplasia has been described in polyps of the gastrointestinal tract [8, 9]. Although a variety of inflammatory or neoplastic conditions of the sinonasal tract can contain very radiodense material, either calcification or ossification, on
1180
computed tomography (CT) scans, its presence is generally believed to be a useful sign to narrow the differential diagnosis, even if we may not be confident of the pathologic nature of this radiodense material [10]. It can represent dystrophic calcification accompanying chronic inflammation or a necrotic tumor, calcification or ossification associated with a cartilage- or bone-forming tumor, heterotopic metaplastic ossification, and residual or fragmented bone as seen in the destructive inflammatory or neoplastic conditions. Radiologic descriptions on nasal polyps with metaplastic ossification are also rare. To our knowledge, only three cases have briefly been reported on the CT features before [4, 5, 7], and there have been no reports on the magnetic resonance (MR) imaging findings. Correct preoperative diagnosis would be important to help determine the most appropriate surgical plan because nasal polyps can be removed simply by the routine endoscopic surgery, whereas many of the sinonasal tumors, either benign or malignant, might require a more extensive surgery. The purpose of this study was to report the CT and MR imaging findings of five cases of pathologically proven nasal polyp with metaplastic ossification.
Methods Subjects This study was approved by our institutional review board. We retrospectively reviewed CT (n=5) and MR (n=3) images obtained from five patients with pathologically proven nasal polyp with metaplastic ossification. The patients were collected from two tertiary academic hospitals between March 2004 and June 2009. There were four men and one woman, aged ranging from 47 to 77 years, with a mean age of 59 years. The patients presented with rhinorrhea (n=3), nasal obstruction (n=1), or headache (n=1), which had first been noticed 1 to 60 months before, with an average duration of 14 months. In no patients was there a history of previous trauma or surgery. All lesions were removed by endoscopic nasal polypectomy and proven to be inflammatory polyps. All of the patients were free of disease without evidence of recurrence on physical examination during the follow-up period of 3–54 months (mean, 20.6 months). Imaging techniques CT scanning was performed in all patients, and MR imaging, in three patients. CT scans were obtained by using various models of a helical CT scanner. CT images were reformatted with a 2.5- or 3.0-mm-thick reconstruc-
Neuroradiology (2010) 52:1179–1184
tion based on 0.6- or 0.625-mm-thick axial images. In four patients, CT scans after the intravenous administration of an iodinated contrast material were available for review; of these four, precontrast CT scans were also available in two. In the remaining one patient, CT scans were obtained without the use of contrast material. MR examinations were performed on various models of a 1.5-T (n=1) or 3-T (n=2) scanner by using a head or neurovascular coil. In all patients, precontrast T1-weighted spin-echo images (TR/TE/NEX, 400–560 ms/10–14 ms/2) and T2-weighted fast spin-echo images (TR/TE/NEX, 2,500–4,500 ms/80–110 ms/1) with fat saturation were obtained, followed by contrast-enhanced, T1-weighted spin-echo images with fat saturation after the intravenous injection of 0.1 mmol/kg of gadopentetate dimeglumine. Images were obtained in at least two planes with 3- to 4mm section thickness and 0- to 1-mm intersection gap. Image analysis Two experienced head and neck radiologists (with clinical experience of 20 and 6 years) retrospectively reviewed all of the CT and MR images for consensus, with emphasis on the location, size, shape, internal architecture, and pattern and degree of enhancement of the lesion. The size of the lesion was measured at the greatest diameter of the lesion. As for internal architecture, we compared the attenuation of the soft tissue components of the lesion on precontrast CT scans and the signal intensity on T1- and T2-weighted MR images with those of the brain stem. On postcontrast CT and MR images, the pattern of enhancement of the lesion was categorized as homogeneous or heterogeneous. The degree of enhancement was also subjectively assessed as being poor, mild, moderate, and marked. We also documented the location and morphologic characteristics of metaplastic ossification on CT and MR images.
Results The CT and MR imaging features of five cases of nasal polyp with metaplastic ossification are summarized in Table 1. All lesions were seen as lobulated (n=3), ovoid (n=1), or dumbbell-shaped (n=1) masses with a mean size of 3.7 cm (range, 2.4–6.5 cm). All lesions were located unilaterally in the posterior nasal cavity and nasopharynx (n=2; Figs. 1 and 2), posterior nasoethmoidal tract (n=2), and maxillary sinus and adjacent nasal cavity in the form of antrochoanal polyp (n=1; Fig. 3). On imaging, none of the cases showed significant erosion of the adjacent bones. Compared with the brain stem, the soft tissue components of all lesions demonstrated isoattenuation on precontrast CT scans, slight hypointensity on T1-weighted MR images
– –
–
(Fig. 1b), and hyperintensity on T2-weighted MR images (Fig. 1c). While all lesions showed poor (n = 2) or heterogeneous mild enhancement (n=2) on postcontrast CT scans, contrast-enhanced MR images demonstrated heterogeneous enhancement with marked peripheral enhancement in two lesions (Fig. 1d) and homogeneous moderate enhancement in one lesion. All lesions contained centrally located radiodense materials on CT scans, the shape of which was multiple clustered in three (Figs. 1 and 3), single nodular in one, and single large lobulated in one (Fig. 2a). The last one also contained a large area of fat on CT scans, which corresponded to fatty marrow of the trabecular bone on histologic examination (Fig. 2b). These radiodense materials on CT scans were seen as hypointensities on all of the MR pulse sequences (Fig. 1b–d). Macroscopically, all lesions were seen as a grayish or pinkish tan, soft tissue or bony mass. Microscopically, all lesions were composed of inflamed and edematous stroma, covered by respiratory epithelium. The stroma contained trabeculae of mature lamellar bone tissues (Figs. 1e and 2b). There was no evidence of cellular atypia or neoplastic tissue proliferation.
Discussion
Size was denoted as the greatest diameter
Density and signal intensity of the lesion were compared with those of the brain stem b
a
Yes/no 5/60/M
T1WI T1-weighted imaging, T2WI T2-weighted imaging
Yes/yes 4/77/M
Maxillary sinus and nasal cavity
6.5
Dumbbell-shaped
Isodense
Poor
Central/multiple clustered
Heterogeneous/marked peripheral enhancement Hyperintense Slightly hypointense Central/single nodular
Yes/yes 3/47/M
Posterior nasoethmoidal
2.6
Ovoid
Isodense
Heterogeneous/ mild
Homogeneous/moderate diffuse enhancement Hyperintense 2.4
Lobulated
Isodense
–
Slightly hypointense
– – –
Central/single large, lobulated, containing fat Central/multiple clustered Yes/no 2/50/M
Posterior nasal cavity and nasopharynx Posterior nasoethmoidal
4.0
Lobulated
–
Poor
Heterogeneous/marked peripheral enhancement Hyperintense Slightly hypointense Central/multiple clustered Heterogeneous/mild – Lobulated 3.2 Yes/yes 1/61/F
Posterior nasal cavity and nasopharynx
T1WIb
T2WIb Location/morphologic characteristics of metaplastic ossification Enhancement pattern/degree Density on precontrast CTb
CT features Shape Sizea (cm) CT/MR image
Location
1181
Case no./age/sex
Table 1 Summary of CT and MR imaging features of five patients with sinonasal polyp with metaplastic ossification
MR imaging features
Enhancement pattern/degree
Neuroradiology (2010) 52:1179–1184
Nasal polyps are the most common expansile lesions in the nasal cavity, which is formed by the accumulation of fluid in the deeper lamina propria of the Schneiderian mucosa of the nasal fossa and paranasal sinuses, usually resulting from allergy, atopy, infection, or vasomotor impairment. Histologically, there are a number of secondary changes with nasal polyps, such as infarction, surface ulceration, mucoid liquefaction, stromal cell atypia, and metaplasia of the surface epithelium [11]. However, metaplastic ossification within nasal polyps is very rare and so far only five cases have been reported in the English language literature [4–7]. This low incidence might be due to a low level of diagnosis. In cases of nasal polyposis, most lesions are removed in pieces and not en bloc, and not all the specimens resected are sent for histologic examination. In addition, even if the specimens with bone content are sent, it is possible to overlook some of these fragments after a definite diagnosis has been obtained with the analysis of other fragments [7]. As for the radiologic literature, only three cases of nasal polyp with metaplastic ossification have been reported on their CT features before [4, 5, 7]. de Vries [4] reported massive nasal polyposis with new bone formation in a patient with a history of sinonasal surgery. Jacono et al. [5] reported a 2-cm lobulated mass with irregular flocculent calcifications in the left posterior choana arising from the
1182
Neuroradiology (2010) 52:1179–1184
Fig. 1 Case 1. Nasal polyp with metaplastic ossification in a 61-yearold woman. a Postcontrast axial CT scan shows a lobulated soft tissue mass with heterogeneous mild enhancement in the left posterior nasal cavity, which extends to the nasopharynx. It contains centrally located, multiple clustered metaplastic ossifications (arrows). b, c Compared with the brain stem, the signal intensity of the mass is slightly hypointense on the T1-weighted image (b) and markedly hyperintense on the T2-weighted image (c). d On the contrast-enhanced T1-
weighted image, there is marked enhancement at the periphery of the mass with the central area being less enhanced. Note that metaplastic ossifications are seen as hypointensities on all of the MR pulse sequences (arrows in b–d). e Photomicrograph shows that the mass is composed of inflamed and edematous stroma (S) which contains mature lamellar bone lined by osteoblasts, representing metaplastic ossification (MO) (hematoxylin–eosin, original magnification, ×100)
Fig. 2 Case 2. Nasal polyp with metaplastic ossification in a 50-yearold man. a Postcontrast axial CT scan shows a large, lobulated mass in the left posterior nasal cavity and nasopharynx (arrows). The majority of the mass is occupied by a large, lobulated bone tissue which contains large area of fat (f). b Photomicrograph shows that the mass
largely consists of mature lamellar bone lined by osteoblasts, representing metaplastic ossification (MO), which is surrounded by inflamed and edematous stroma (S). The trabecular bone contains large area of mature fat (F), representing fatty marrow (hematoxylin– eosin, original magnification, ×40)
Neuroradiology (2010) 52:1179–1184
Fig. 3 Case 5. Nasal polyp with metaplastic ossification in a 60-yearold man. Precontrast axial CT scan shows a large, smooth soft tissue mass in the left maxillary sinus, which protrudes into the posterior nasal cavity through the widened sinus ostium, consistent with antrochoanal polyp. There are centrally located, multiple clustered metaplastic ossifications within the mass (arrow)
posterior nasal septum. Marquez Moyano et al. [7] reported a large, expansile, lobulated soft tissue mass with trapped bone in the right middle meatus, which extended to the ipsilateral maxillary and ethmoid sinuses. Although the exact pathogenesis of metaplastic ossification associated with nasal polyps is still unknown, two theories have been proposed. The first and more appealing theory implies that pleuripotential cells, which are either present in the mucosal polyp or dedifferentiated from cells present in the polyp, may later differentiate along an osteoblastic lineage leading to ossification [5–7]. According to this theory, the differentiation process of osteoblasts includes at least two stages: the early stage of the commitment of undifferentiated mesenchymal cells into osteoblast progenitors and the late stage of the maturation of osteoblast progenitors into osteoblasts, which express various phenotypes of boneforming cells. Bone morphogenetic proteins and transforming growth factor β-1 have been reported to be involved in ectopic bone formation [5]. The second and less plausible theory on the pathogenesis of metaplastic ossification is related to the triggering effect of prior surgery. This theory postulates that new bone formation might arise from bony remnants left behind during previous surgery [4]. However, in four of five previously reported cases as well as all of five cases in the present study, no history of previous sinonasal operation existed, making this theory unlikely. On CT and MR imaging, nasal polyps are usually seen as homogeneous soft tissue masses with smooth, outwardly convex margins [11]. The attenuation on CT scans and the signal intensity on MR images depend on the protein and water contained in nasal polyps. Recently developed polyps tend to have a lower attenuation on CT scans and low to
1183
intermediate T1-weighted and high T2-weighted signal intensities on MR images, reflecting the long T1 and T2 relaxation times, with mucosal enhancement occasionally seen at the polyps’ surface. In contrast, those polyps that have a high protein concentration within the fluid tend to have a higher attenuation on CT scans and high T1weighted and low T2-weighted signal intensities on MR images, reflecting the shortening of the T1 and T2 relaxation times [1, 2, 11]. When sufficient time passes by to develop stromal fibrosis and neovascularization within the polyps, various degrees of enhancement may be seen on postcontrast CT and MR images. In the present study, metaplastic ossification appeared on CT scans most commonly as multiple clustered radiodensities seen in three cases. Single nodular and single large lobulated radiodensities were seen in one case each. For the differential diagnosis of calcified sinonasal lesions, it may be useful to analyze the pattern of radiodensities on CT scans. In general, calcification is favored when the densities are small, spherical, multiple, clumped in one area, or ringlike in appearance, whereas ossification is suggested by the presence of trabecular pattern [10]. However, many of these distinctions cannot be made on imaging preoperatively, as CT cannot always distinguish calcification, ossification, and residual bone. Moreover, significant overlaps may exist in the pattern of these radiodensities among various pathologic entities. A variety of pathologic conditions can mimic nasal polyp with metaplastic ossification on CT and MR images and include nontumorous conditions, such as rhinolith (sinolith) and mycetoma, and tumorous conditions, such as inverted papilloma, chondrosarcoma, osteosarcoma, and fibroosseous lesions [10]. A rhinolith (sinolith) is a calcareous concretion in the nasal cavity or paranasal sinuses with the pathogenesis being not fully understood [12, 13]. Two types of rhinolith exist: exogenous and endogenous. There have been reports on the rhinoliths associated with nasal polyp, the CT findings of which are similar to those of ours [12, 13]. It may be that endogenous rhinolith actually represents dystrophic calcification or metaplastic ossification associated with chronic sinonasal infection [11]. Sinonasal mycetoma typically appears on CT scans as a hyperattenuating lesion that frequently contains centrally located punctate, linear, or nodular calcifications with the rate of 51–77% [14, 15]. On MR images, mycetoma demonstrates marked diffuse hypointensity on T2-weighted images with no enhancement after injection of contrast material [14], which can give an additional clue if the diagnosis is doubtful on CT scans. Although apparent calcifications can be demonstrated within sinonasal inverted papilloma on CT scans, most of these radiodensities are histologically residual bone fragments with calcifications making up of only a small
1184
Neuroradiology (2010) 52:1179–1184
proportion [10]. Sinonasal inverted papilloma frequently causes focal hyperostosis, which is a reliable CT sign to predict the site of origin [16]. MR imaging can give a specific clue to the diagnosis of inverted papilloma by demonstrating convoluted cerebriform pattern on T2weighted and contrast-enhanced T1-weighted images [17]. Chondrosarcoma may be difficult to be differentiated from nasal polyp with metaplastic ossification on CT scans because both conditions manifest as soft tissue mass with multiple flocculent calcifications. In the nasal cavity, chondrosarcoma tends to occur in the cartilaginous nasal septum and marginal bone erosion is typically present [18]. Osteosarcoma has well-defined or ill-defined radiodensities on CT scans, which are diffusely distributed within the mass [10]. Unlike nasal polyps, focal bone destruction is frequent with osteosarcoma, typically with a sunburst periosteal reaction [18]. Fibroosseous lesions, such as fibrous dysplasia and ossifying fibroma, are centered in bone. On CT scans, the radiodensities associated with fibroosseous lesions are well defined and distributed diffusely within the mass [10]. There are two limitations of this study. First, the case series is small, consisting of only five cases. However, rarity of the diagnosis makes five cases a large series that equals the number of published cases. Second, our study is retrospective in which the type of radiological studies performed is not homogeneous. Not all patients had nonenhanced CT scans. This heterogeneity in the methods of CT scanning is mainly caused by the different imaging protocols used in two institutions. In conclusion, although rare, metaplastic ossification can occur within nasal polyps. The possibility of its diagnosis may be raised when one sees a benign-looking sinonasal mass with centrally located radiodense materials on CT scans. It is important to bear in mind that although the presence of radiodensities within a sinonasal lesion at CT may help narrow the differential diagnosis, significant overlaps of the pattern of these radiodensities may exist among various pathologic entities. MR imaging may be useful when mycetoma or inverted papilloma cannot be ruled out on CT scans.
Conflict of interest statement of interest.
We declare that we have no conflict
References 1. Eggesbø HB (2005) Radiological imaging of inflammatory lesions in the nasal cavity and paranasal sinuses. Eur Radiol 16:872–888 2. Mafee MF, Tran BH, Chapa AR (2006) Imaging of rhinosinusitis and its complications. Clin Rev Allergy Immunol 30:165–185 3. Baird AR, Hilmi O, White PS, Robertson AJ (1998) Epithelial atypia and squamous metaplasia in nasal polyps. J Laryngol Otol 112:755–757 4. de Vries N (1988) New bone formation in nasal polyps. Rhinology 26:217–219 5. Jacono AA, Sclafani AP, van de Water T, McCormick S, Frenz D (2001) Metaplastic bone formation in nasal polyps with histologic presence of transforming growth factor beta-1 (TGFb-1) and bone morphogenetic proteins (BMPs). Otolaryngol Head Neck Surg 125:96–97 6. Ramachandran K, Thomas MA, Denholm RB (2005) Osseous metaplasia of a nasal polyp. J Otolaryngol 34:72–73 7. Marquez Moyano JA, Navarro Cantero A, Garrido Iniesta FJ et al (2007) Metaplastic ossification in nasal polyp. Acta Otorrinolaringol Esp 58:276–277 8. McPherson F, Maldonado M, Truitt CA, Mamel JJ, Morgan MB (1999) Metaplastic ossification of a benign colonic polyp: case report. Gastrointest Endosc 49:654–656 9. Nakajima H, Iwane S, Mikami T, Nara H, Yamagata K, Morita T, Yagihashi S (1997) Osseous metaplasia in benign rectal polyps. J Clin Gastroenterol 25:558–559 10. Som PM, Lidov M (1994) The significance of sinonasal radiodensities: ossification, calcification, or residual bone? AJNR Am J Neuroradiol 15:917–922 11. Som PM, Brandwein MS (2003) Inflammatory diseases. In: Som PM, Curtin HD (eds) Head and neck imaging, 4th edn. Mosby, St Louis, pp 193–259 12. Kanzaki S, Sakamoto M (2005) Sinolith in the ethmoid sinus. J Laryngol Otol 120(e11):1–3 13. Ozcan I, Ozcan KM, Ensari S, Dere H (2008) Rhinolithiasis with a nasal polyp: a case report. Ear Nose Throat J 87:150–151 14. Aribandi M, McCoy VA, Bazan C (2007) Imaging features of invasive and noninvasive fungal sinusitis: a review. Radiographics 27:1283–1296 15. Yoon JH, Na DG, Byun HS, Koh YH, Chung SK, Dong HJ (1999) Calcification in chronic maxillary sinusitis: comparison of CT findings with histopathologic results. AJNR Am J Neuroradiol 20:571–574 16. Lee DK, Chung SK, Dhong H-J, Kim HY, Kim HJ, Bok KH (2007) Focal hyperostosis on CT of sinonasal inverted papilloma as predictor of tumor origin. AJNR Am J Neuroradiol 28:618–621 17. Jeon TY, Kim H-J, Chung S-K et al (2008) Sinonasal inverted papilloma: value of convoluted cerebriform pattern on MR imaging. AJNR Am J Neuroradiol 29:1556–1560 18. Som PM, Brandwein MS (2003) Tumors and tumor-like conditions. In: Som PM, Curtin HD (eds) Head and neck imaging, 4th edn. Mosby, St Louis, pp 339–349