This series of primary sacral tumors treated at our tumor center provide valuable data of epidemiological characteristics contributing to our understanding of the diagnosis and therapy for primary bone tumors at the sacrum in the clinical practice. Available reports on the epidemiologic features of primary spine tumors were mostly among the mobile spine[1, 4, 5]. The present report demonstrated epidemiologic characteristics based on the largest series of primary sacral tumors.
In our series, chordoma was the most common primary malignant tumor, accounting for 44.1% (316/716), followed by chondrosarcoma (10.3%, 74/716), myeloma (7.4%, 53/716), malignant peripheral nerve sheath tumor (6.6%, 47/716), Ewing sarcoma (6.6%, 47/716), osteosarcoma (5.6%, 40/716) and lymphoma (4.9%, 35/716).
Chordoma is a relatively rare neoplasm and accounts for 1%-4% of all primary malignant bone tumors which arise from embryonic remnants of notochord. It has been reported that chordomas occur most commonly within the sacrum (50–60%), followed by the spheno-occipital vertebrae (25–30%), cervical region (10%) and thoracolumbar vertebrae (5%) and chordoma affects males more commonly than female. Our results also showed the male predominance was most pronounced among 306 chordomas, accounting for 68.6% and age of 51–70 yrs was the most common of age interval, which was concordant with the previous studies. The peak age in our cohort was the range of 51 to 60 and it was distinctly uncommon in patients younger than 30 years, only accounting for 5.9% (18/306).
Chondrosarcomas (CS) rank the second in the incidence of all primary malignant bone tumors, with reporting about 25% incidence and following after osteosarcoma. Regarding age, it is more common in adults between 40–80 years old, and is slightly more common in men. CS constituted over 20.4% of the malignant tumors in Mayo Clinic series and more than two-thirds of chondrosarcomas were in the trunk and the upper ends of the femur and humerus. CS was a relatively rare and the incidence at the sacrum was 1.9% (24/1293) among all chondrosarcomas in Mayo Clinic series. However in our cohort, the analysis of epidemiological feature of CS showed an obvious predilection of male (M: F = 1.24:1) and the peak age ranged from 41 to 50 years. Moreover, chondrosarcoma was the second common histological type at the region of the sacrum for the primary sacral malignant tumors and the incidence of CS among the malignant tumors was 10.3% (74/716).
Myeloma, a tumor of hematopoietic derivation, is the most common primary neoplasm of bone. There were more than 5000 patients with myeloma documented in the Mayo Clinic files. They reported 67.7% were males and the largest concentration of age was in the sixth and seventh decades of life. The well-known rarity of myeloma in patients who were younger than 40 years was shown in the Mayo Clinic series. Likewise, myeloma at the sacrum had the gender predilection (M: F = 2.12:1) and 67.9% of all myelomas were males in our series. The median age of myeloma was 54.1 ± 13.2 yrs and the peak age ranged from 41 to 50 years. Only two patients in our cohort were younger than 30 years and no patient was in the first and second decades of life. Generally, the epidemiological characteristics of sacral myeloma were similar to other boney myeloma.
Malignant peripheral nerve sheath tumors (MPNST) include malignant schwannoma (malignant peripheral schwannoma) and neurofibrosarcoma. MPNST represents a relatively common subtype of soft tissue sarcoma and is particularly likely to occur in individuals with type 1 neurofibromatosis (NF1)[10–13]. A SEER database analysis showed 64 MPNST in the spinal location. Their mean age at diagnosis was 50.9 years with more patients in the higher age group and fifty-six percent of patients were male. However, it had no description of the incidence at the sacrum. In our cohort, the analysis of epidemiological feature of MPNST showed an obvious predilection of female (M: F = 0.68:1) and the peak age ranged from 41 to 50 years. Our result showed the epidemiologic characteristic of age predilection was in concordance with the previous study in SEER database, but gender predilection of MPNST at the sacrum was not similar to the result of SEER database .
Ewing sarcoma (ES) is a distinctive, small, round cell sarcoma that is considered one of the most lethal of all bone tumors. In Mayo Clinic database, ES comprised 8.6% of the total malignant tumors and had a distinct predilection for males (62%). Furthermore, appromimately 75% were in the first two decades of life and the incidence of ES at the sacrum accounted for 5.9% (36/611) of all patients with ES. The sacrum is not the frequent site for Ewing sarcoma. In our PKUPH database, Ewing sarcoma located at the sixth top of all primary sacral malignant tumors. The peak incidence was in the second decade (40.4% of all 47 Ewing sarcomas), followed by the third and fourth decades (38.2%) and it had no predilection of gender, which was not concordant with the Mayo Clinic experience.
Osteosarcoma is the most common malignant bone tumor. Mayo Clinic series files recorded 1952 osteosarcomas, accounting for 27.5% of all malignant tumors and 19.2% of all bone tumors and approximately 58% of patients with OS were male. In their database, the incidence of OS at the sacrum accounted for 2.0% of all patients with OS and the anatomic site around the knee was the most common site. The second decade was the most common age distribution and among 1952 osteosarcomas, 192 patients were older than 60 years who had the preexisting condition such as Paget disease, previous radiation, infarct, chronic osteomyelitis and cyst of degenerative joint disease as the second peak. According to our results, osteosarcoma at the sacrum was not frequent as the site around the knee and placed as the sixth top of all primary sacral malignant tumors. Although only one patient with the sacral OS was in the first decade of life, the peak incidence was in the second decade (37.5% of all 40 osteosarcomas), followed by the third decade (32.5%). We noticed no one patient aged more than 60 years. This result demonstrated that the age distribution of sacral osteosarcoma had the peak age of 11–20 and didn’t show another age peak of more than 60 years. Moreover, osteosarcoma was not common at the region of sacrum.
Bone lymphoma is a rare disease. It is estimated that bone lymphoma is accounting for about 5% of extranodal lymphomas and 3–7% of all malignant bone tumors. Parker et al. firstly described the malignant lymphoma of bone and separated it from Ewing sarcoma. The Mayo Clinic database showed the 905 cases of malignant lymphoma comprised as 12.7% of the malignant bone tumors in their series and males predominated at a ratio of 4 to 3 in their cohort. In our cohort, approximately 51.4% of lymphoma occurred in patients between 41–60 years, with a peak incidence in the fifth and sixth decade of life. Only 5.7% of the patients with lymphoma were younger than 20 years and no one was younger than 10 years old. However, our series revealed lymphoma at the sacrum had the female predilection (M: F = 0.75:1), which was not concordant with the Mayo Clinic experience.
Our PKUPH database showed that giant cell tumor (30.6%, 205/669) was the most frequent benign tumors, followed by neurofibroma (23.2%, 155/669), schwannoma (17.8%, 119/669), tuberculosis (3.6%, 24/669), teratoma (3.4%, 23/669), sacral canal cysts (3.3%, 22/669) and epidermoid cyst (3.1%, 21/669). The epidemiological characteristics of primary sacral benign tumors were distinct from the one of spinal benign tumors. It has been reported that hemangioma was the most frequent benign primary spine tumor in one hospital of China, which was different from the region of sacrum and our database showed giant cell tumor was the most common histological type at the sacrum . Hemangioma at the sacrum accounted for 2.1% (14/669) of all sacral benign tumor and 1.0% (14/1385) of all PST. It illustrated that hemangioma was not a frequent tumor at the sacrum.
Giant cell tumor (GCT) is an invasive benign bone tumor consisting of proliferative mononuclear cells and osteoclast-like multinucleated giant cells. In the present study, GCT was the most common benign tumor at the sacrum and the incidences of GCT among all PST and primary sacral benign tumors were respectively 14.8% (205/1385) and 30.6% (205/669). This result was concordant with the study of Zhou et al about the epidemiological feature of all spinal tumors. The Mayo Clinic series showed the female predominated in bone GCT, with 376 females and 295 males. However, Niu et al. reported 621 patients with GCT in the extremity and male predominance (1.4:1) was observed in their series. Their epidemiological feature of extremities was different from the characteristics of our sacral GCT and this illustrated that predominate gender may depend on the anatomical site. Our cohort also had 110 cases of female, accounting for 53.7% of all GCTs in our series. Approximately 79.5% of GCT occurred in patients between 21–50 years, with a peak incidence in the third and fourth decade of life. Only 8.8% of the patients with GCT were older than 50 years and only 11.7% of GCT occurred in patients before 20 years old. Furthermore, no one was younger than 10 years old.
Benign peripheral neurogenic tumors include neurofibroma and peripheral schwannoma. Neurogenic tumors arising from the sacrum are rare, with only about 7% of intraspinal neurogenic tumors involving the sacrum. Neurofibromas can occur in any site, both deep soft sissue and superficial cutaneous lesions. They are usually painless and they are often excised for cosmetic purpose. Individuals with NF1 may have multiple neurofibromas that need excision for functional purpose as well as to exclude the possibility of malignant transformation. The analysis of epidemiological feature of neurofibroma in our series showed a little predilection of female (M: F = 0.80:1) and the peak age ranged from 41 to 60 years. Meanwhile, schwannomas are relatively common benign lesions of the peripheral nerves, which are thought to derive from Schwann cell. They affect all age groups and are usually solitary sporadic tumors. Schwannomas can also develop along the spine adjacent to the neural foramina and frequently show a “target sign” on imaging that can be very suggestive of this specific diagnosis. They are usually slow growing and often discovered incidentally. It has been reported that sacral schwannomas typically occur in middle-aged patients without any predilection for gender. Pennington et al. performed a systematic review and reported presacral schwannoma can reasonably be treated with either en bloc or piecemeal GTR and recurrence was infrequent. In their review, the patients showed no gender predilection. Our database analysis revealed epidemiological feature of schwannoma also had no gender predilection and the peak age ranged from 31 to 60 years. This result was concordant with the result of previous study in the literature.
Over the past decades, the incidence of boney tuberculosis has continued to increase due to population growth, acceleration of mobility. Little is known about the incidence of spinal tuberculosis. In our cohort, we evaluated the incidence of sacral tuberculosis, which was the fourth top of sacral benign tumors (3.6%, 24/669). Moreover, it had the female predilection and it occurred in a patient of any age.
Sacrococcygeal teratoma is the most common extragonadal germ cell tumor in neonates and infants[19–21]. However, this lesion sometimes occurs in the adults. This lesion consists of a solid and/or cystic component and develops either from the tip of the sacrum, protruding outward from the buttocks, or within the pelvic cavity. In our series, the analysis of epidemiological feature of sacrococcygeal teratoma also showed obvious gender predilection and females occurred in 82.6% of all patients with teratoma. Moreover, the peak age ranged from 21 to 40 years and this feature of age distribution may have some bias due to having more adult cases not neonates and infants in our tumor center.
Epidermoid cysts of spinal lesions are very rare and they are often found in the lumbosacral region, which are commonly intradural-extramedullary tumors[22–24]. They commonly occur in children and the cause of epidermoid cysts is believed to be the introduction of ectoderm cells arising in early fetal life between 3 and 5 weeks. The formation of epidermoid cysts may be associated with defective closure of the dural tube. Epidermoid cysts in our cohort had 17 cases of female, accounting for 81% of all epidermoid cysts in our series. Approximately 42.9% of epidermoid cysts occurred in patients between 41–60 years. It also had significant gender predilection and females occurred in 81% of all patients with epidermoid cysts, like the epidemiologic feature of sacrococcygeal teratoma.
In conclusion, the large cohort of primary sacral tumors in our database may reveal their epidemiologic characteristics of primary sacral malignant and benign tumors in China and epidemiological feature of PST is fairly distinct from the mobile spine and extremities.