Phosphaturic mesenchymal tumor (PMT) is a rare, slowly progressive, histomorphologically distinct entity of tumors that can emerge anywhere in the body. According to World Health Organization, PMT has two pathological types: benign and malignant. PMT was discovered due to tumor-induced osteomalacia (TIO) and is increasingly accepted in recent years as the leading cause of TIO. However, most published reports have focused on the clinicopathological, immunohistochemical, and molecular genetic studies on PMT rather than the radiological work-ups.[3,4] Hence, the aim of this study was to find the common imaging characteristics of PMT to assist clinical diagnosis.
The radiology and pathology databases of Beijing Jishuitan Hospital were retrospectively reviewed for pathologically proven PMT. A total of 25 patients were initially retrieved. Among them, four patients were excluded because the lesions were postoperative tumor relapse or metastasis, and three patients were excluded for incomplete radiological data. Finally, 18 primary cases were included.
A total of 18 PMTs from 18 patients (10 males, 8 females) were reported in this study. The average age at the time of hospital visit was 37.3 ± 16.3 years (range: 3.0–58.0 years). The clinical features are described in Supplementary Table 1, https://links.lww.com/CM9/B428. One patient in routine physical examination did not show any discomfort. Symptoms of osteomalacia were observed in 5/18 patients, while the remaining presented focal pain (n = 10), focal lump (n = 2), and shortening of the finger (n = 1) owing to the tumor lesions. The median duration from symptom onset to pathological diagnosis of PMT with and without osteomalacia symptoms were 24.75 months (0–9.8 years) and 5.75 months (0.8–27.0 years), respectively. All tumors were pathologically benign. Two lesions recurred at 29.0 months and 39.5 months after surgery, respectively.
All laboratory values were obtained within 1 month of the imaging scan. The results showed that 9/18 patients had hypophosphatemia, of whom five had low serum calcium parameters. Additionally, 3/18 patients had elevated alkaline phosphatase levels, and 4/5 patients had low serum 25(OH)VitD3 levels (10.78 ± 4.59 ng/dL, range: 6.66–16.33 ng/mL, normal value: 20.00–40.00 ng/mL). Moreover, 2/6 patients had elevated full-length parathyroid hormone levels (90.15 pg/mL, range: 71.00–109.30 pg/mL, normal value: 15.00–65.00 pg/mL).
Signs of osteomalacia, such as obscure or disappeared trabecular structures, insufficiency stress-type fractures (n = 3), and deformities in thoracic cage, spine, pelvic, and lower extremities, were observed in five patients. For anatomical imaging analysis, the lesions were divided into those originating from bone (n = 15), soft tissue (n = 2), and sinuses (n = 1).
Fifteen lesions arose from bone with 9 (ilium [n = 7] and spine [n = 2]) from axial skeleton and 6 (femur [n = 2], metacarpus [n = 2], scapula [n = 1], and tibia [n = 1]) from appendicular skeleton. The mean maximal lesion diameter was 5.77 ± 2.74 cm (range: 2.65–10.90 cm). Additionally, 13/15 lesions showed a narrow zone of transition with partial sclerotic boundary, bony shell in 11/13, and 1/13, respectively (Figure 1A). All 15 lesions had partial cortical bone abruption, while 3/15 had extraosseous soft tissue components. The pathological fracture caused by the tumor was observed in 3/15 lesions. A total of 14 patients underwent CT (computed tomography) examinations, among whom 13 were evaluated by contrast CT. All 14 patients had osteolytic lesions with slight and obvious expansions in 5 and 3 cases, respectively. Calcification was observed in 10/14 lesions, and 4/10 exhibited a substantial phenotype [Figure 1A]. Ground glass density and fat density were observed in 7/14 and 5/14 lesions, respectively. The enhancement pattern characterised by obviously even, obviously uneven, intermediately uneven, and slightly uneven were seen in 1/13, 8/13, 3/13, and 1/13 cases, respectively. Furthermore, eight patients underwent plain and contrast MRI (nuclear magnetic resonance) examinations. Consequently, 6/8 lesions were heterogeneous on T1-weighted imaging, while 1/8 was slightly hypointense and 1/8 was iso-intense [Figure 1B]. All lesions were heterogeneous on T2-weighted imaging. Also, cystic changes, intratumoral bleeding, internal fluid–fluid level, and perilesional edema were detected in 2, 2, 1, and 2 lesions, respectively. Dark T2 was present in 7 lesions, with 5 corresponding to calcification or ground glass density observed on CT scan [Figure 1C]. All eight patients showed obvious enhancement after IV gadolinium injection (7 heterogeneous and 1 homogeneous). Two patients underwent dynamic contrast-enhanced MRI, and both time-signal intensity curves demonstrated a platform pattern.
Two lesions arose from soft tissue with one in the upper arm and the other in the trunk. The mean maximal diameter was 1.83 cm (range: 1.71–1.95 cm). Both lesions showed even density with clear margin on plain CT scan, and obvious even enhancement on contrast scan. One of the lesions invaded into the adjacent bone.
One lesion arose from sinuses invading into the left frontal sinus, left maxillary sinus, and left orbit. The maximal diameter of the lesion was 6.38 cm. It had a clear margin but involved the adjacent bony structure. Also, a lot of fat density was observed. It was uneven and distinctly uneven on plain and contrast CT scan, respectively, and heterogeneous on T1WI (T1-weighted imaging) and T2WI (T2-weighted imaging).
The results showed that 9/12 lesions revealed an increased bone uptake by bone scintigraphy [Figure 1D], 1/1 lesion showed hypermetabolic characteristics by 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG PET/CT), and 1/1 lesion with octreotide scanning showed a positive uptake in the tumor location.
The current study emphasized the under-recognition of non-phosphaturic PMT by the fact that only 5/18 patients presented with symptoms of osteomalacia.
This cohort confirmed that PMT might have some unique features. Typically, all lesions were monostotic, and the density or signal was usually homogeneous if it was small (as our two lesions originated from soft tissues), which became inhomogeneous with growth. For tumors arising from bone, the lesions were osteolytic, sometimes with expansion and a component of fat, and most of them demonstrated variable amounts of ground glass density, foci of cartilage, or ossification on CT, corresponding to dark T2WI signal on MR, related to the pathological grungy and flocculent calcification. They sometimes demonstrate insufficiency fracture, caused by the hypocalcemia secondary to hypophosphatemia. These phenomena were consistent with those observed previously. Also, there are some contradictions about the growth pattern. Interestingly, our lesions tended to display a narrow zone of transition with well-formed and sometimes sclerotic margins (even nearly complete bony shell in one lesion), suggesting a slow process and non-aggressive nature. On the other hand, all lesions had interrupted cortical bone, some of which were associated with intralesional hemorrhage and internal fluid–fluid levels, suggesting rapid growth. These phenomena in addition to soft tissue lump and perilesional edema that stood for histological focal invasiveness indicated aggressive biological behavior. For the tumor in sinuses, we found no grungy calcifications but salient lipid components. Other studies showed similar findings, indicating that this feature might be crucial for sinonasal PMT.
In conclusion, PMT may have some common features. The combination of imaging and clinical features can improve the accuracy of diagnosis. However, more cases still need to be investigated.
The study was funded by grants from the Beijing Bureau of 215 Program (No. 2013–3-033; 2009–02-03).
Conflicts of interest
1. Folpe AL. Phosphaturic mesenchymal tumors: a review and update. Semin Diagn Pathol 2019;36:260–268. doi: 10.1053/j.semdp.2019.07.002.
2. WHO classification of tumours editorial board. Soft tissue and bone tumours. 5th ed. Lyon: International Agency for Research on Cancer, 2020.
3. Yamada Y, Kinoshita I, Kenichi K, Yamamoto H, Iwasaki T, Otsuka H, et al. Histopathological and genetic review of phosphaturic mesenchymal tumours, mixed connective tissue variant. Histopathology 2018;72:460–471. doi: 10.1111/his.13377.
4. Wu H, Bui MM, Zhou L, Li D, Zhang H, Zhong D. Phosphaturic mesenchymal tumor with an admixture of epithelial and mesenchymal elements in the jaws: Clinicopathological and immunohistochemical analysis of 22 cases with literature review. Mod Pathol 2019;32:189–204. doi: 10.1038/s41379-018-0100-0.
5. Broski SM, Folpe AL, Wenger DE. Imaging features of phosphaturic mesenchymal tumors. Skeletal Radiol 2019;48:119–127. doi: 10.1007/s00256-018-3014-5.