Background

Primary bone tumors usually occur in extremities and seldom occurs in the spine (primary spinal tumors compromising 2.8% of all primary bone tumor cases) [1]. While primary spinal osteosarcoma, which accounts for 0.85% - 3.0% of all osteosarcomas [2], only constitutes 3.6% to 14.5% of primary spinal tumors cases [1,3]. For the anatomical location of primary spinal osteosarcoma, only 12.5% -22.7% are located in the thoracic region, with lumbosacral region constituting more than 70% of the cases [1,4]. The mean age of diagnosis for primary spinal osteosarcoma is 38-46 years old [4,5], while some quoted a bimodal distribution of age for all primary osteosarcoma: younger group peaking in adolescence (<20 years old) and the older group peaking after 65 years old. [6]. The most common presenting symptom of patients suffering from primary spinal osteosarcoma is pain, which was reported in around 90% of cases [1,4]. Neurological deficit is also a common presenting symptom, ranging from 55% to 87.5% of cases [1,4].

As a locally destructive tumor with strong potential for systemic metastasis, the prognosis of primary spinal osteosarcoma is worse when compared with osteosarcoma of the extremities [4] or when compared with other common primary spinal tumors (e.g. chordoma, chondrosarcoma, Ewing’s sarcoma etc.) [5]. With aggressive interdisciplinary treatment, the median survival is 18-23 months. Surgical resection of the tumor is a strong factor beneficial to overall survival and cancer-specific survival, independent of patient’s age, the extent of local tumor invasion, tumor location or even staging of the tumor [4,5,8]. A review of 158 patients in the United States showed a significantly longer median survival for the surgical group versus the group with no surgery done (37 months versus 11 months) [5]. A multicenter review of 58 patients showed the median survival of primary spinal osteosarcoma can even be as long as 6.8 years with appropriate surgical resection done [9].

For surgical resection of musculoskeletal tumors, the Enneking surgical staging system is one of the most quoted systems, which suggests malignant musculoskeletal tumors require at least an en bloc wide margin excision [10]. However, spinal tumor often abuts the dura, nerve root or the nearby vasculature, making wide resection of spinal tumor always impossible or with a devastating cost. As a result, other systems were developed. The Weinstein-Boriani-Biagini system (WBB system) is an anatomical descriptive classification for spinal tumor, providing guidance towards possible type of resection (aiming for en bloc but not necessarily wide excision) [11,12]. Meanwhile Tomita et al. introduced a new concept for spinal tumor in which each vertebra could be regarded as a single oncologic compartment. [13] Different large-scale reviews have showed that en bloc excision of primary spinal osteosarcoma with a clear margin (not necessarily a wide margin) leads to lower rate of local recurrence and greater median overall survival [4,9,14,15]. An aggressive en bloc excision aiming for a clear margin should be performed at first attempt as tumor recurrence significantly shortened patient survival [14]. Despite encouraging results of en bloc excision for primary spinal osteosarcoma, it is also well known for its high perioperative complications, including massive bleeding, spinal cord injury, pleural fluid leakage, cerebrospinal fluid leakage etc. [16, 17].

Other treatment modalities for primary spinal osteosarcoma have also been studied in the literature, mainly being chemotherapy and radiotherapy. A combination of neoadjuvant chemotherapy, surgical resection and post-operative chemotherapy offers higher survival rate and longer duration before metastasis occurs [4, 18]. A systemic review favored three-drug regimens over two-drug regimens, for example using a combination of methotrexate, adriamycin and cisplatin [19]. Postoperative radiotherapy can be offered for some patients, e.g. in cases of positive or inadequate margin, and may lead to survival benefit [4, 5, 18].

The aim of this case report is to present a case of atypically presented spinal osteosarcoma which was treated with a single-staged en bloc excision, the outcome and its future implication.  

Case Report

This is a case of an incidentally found T1 vertebral osteosarcoma in a 28-year-old lady. This lady enjoyed good past health. She attended a pre-employment body check and the chest x-ray showed a mixed sclerotic lytic T1 lesion (figure a). 

Figure a

The arrow marked the mixed sclerotic lytic T1 lesion seen in the private chest x-ray.

Physical examination of this lady showed no swelling nor any tenderness over the spine. Her neck range of movement was full and neurological examination was unremarkable. CT and MRI showed an aggressive-looking lesion at T1 vertebrae involving the left posterior elements, the left inferior articular process of C7, head of the left 2nd rib and left superior articular process of T2 (figure b). There was an overlying soft tissue component, measuring 3.5cm x 2.7cm x 4.8cm with no intraspinal involvement (figure c). For the WBB system, 1 to 5 sectors with tissue layers A to C were involved. For Tomita system, this tumor was classified as type 6. The surrounding nerve roots, brachial plexus and subclavian vessels were not involved. Histopathology revealed findings compatible with high-grade osteosarcoma. PET scan showed there was no distant metastasis.

Figure b

CT imaging of the osteosarcoma.

Figure c

MRI imaging of the osteosarcoma, demonstrating the soft tissue component

Oncologist offered neoadjuvant chemotherapy in view of possibility of micro-metastasis. However, she showed poor tolerance to chemotherapy with significant fatigue and repeated vomiting. She refused to continue chemotherapy after only half cycle. Interval CT scan and MRI were done, which showed no significant change in size of the osteosarcoma and there was also no evidence of lung metastasis. With her young age, good premorbid status and absence of metastasis, total en bloc excision of the T1 osteosarcoma was offered. In order to allow en bloc excision of tumor, excision of vertebrae, adjacent ribs and selective nerve roots ligation are contemplated. Before the operation, the likelihood of left upper limb weakness following the resection of C8 to T2 nerve roots was discussed thoroughly with this lady. MR arteriogram of the circle of Willis was done, showing hypoplastic right posterior communicating artery and fetal configuration of the left posterior cerebral artery. In case ligation of the left vertebral artery was warranted intra-operatively, it would lead to an increase risk of ischemic stroke in view of incomplete circle of Willis. A 3D-printed model was obtained before the operation for better visualization and analysis of the complex anatomy around the tumor and operative planning. Cardiothoracic surgeon and vascular surgeon were invited to join the operation in order to facilitate tumor exposure before excision.

Figure d

The 3D-printed model showing the T1 osteosarcoma in relation with the major surrounding structures: tumor in green, nerve roots in yellow, aorta and its major branches in pink, major veins in blue.

Figure e

The planned excision margin demonstrated with the 3D-printed model and CT imaging in red lines.

The en bloc excision was started with posterior approach and baseline somatosensory evoked potential (SSEP) and motor evoked potential (MEP) signals were obtained. Posterior incision was designed over the midline to include the biopsy tract (with 0.5cm margin from the biopsy site) and extended obliquely along the course of left 2nd rib. Muscles overlying the tumor, including the left trapezius, left levator scapulae and left paraspinal muscles were cut proximally and distally to keep the tumor en bloc. Right hemilaminectomy of C7 to T2 was followed by the division of left T1 and T2 nerve root with aneurysmal needle from the right side. Complete facetectomy of left C6/7 and T2/3 level were performed, separating the left lamina of C6 from C7 and that of T2 from T3 respectively. Instrumentation was performed for temporal fixation and patient was turned supine.

Figure f

The head was over the right side in both photos. The left photo showing an attempt to ligate the nerve roots while the right photo showing the tumour was kept en bloc with surrounding muscles cut.

With a median sternotomy, the left subclavian vessels, which were located on the surface of the 1st rib, were mobilized before the osteotomy of 1st rib. The left vertebral artery was dissected free from T1 and T2 bodies, meanwhile other critical neurovasculatures over the left anterior neck were protected, including the carotid artery, subclavian vessels, internal jugular vein, vagus nerve and phrenic nerve. The inferior trunk of the brachial plexus was identified (with nerve stimulator) and divided. Vertical osteotomies were performed over the T1 and T2 vertebral bodies with burr. Left partial discectomies were performed at the C7/T1 and T2/3 levels.  

Figure g

The yellow arrow showing the left vertebral artery being dissected free from the T1 and T2 vertebral bodies.

The patient was turned prone again for tumor excision and posterior instrumentation. Osteotomies were performed over the left 2nd and 3rd rib. Left C8 nerve root was ligated. The T1 osteosarcoma was excised en bloc, removed with the left C7, T1 and T2 vertebrae, the proximal left 1st to 3rd ribs, the left C8 to T2 nerve roots, the parietal pleura and the surrounding paraspinal muscles. Posterior spinal instrumentation was performed from C4 to T5 level. A rotational right trapezius muscle flap was fashioned to cover the left lung apex and the spinal instrumentation. The SSEP and MEP signals were checked repeatedly, with same signal recorded over the right upper limb and bilateral lower limbs. During this 30-hour operation, around 15L of blood loss was recorded, mainly being oozing from the large raw area with no major vessels damaged inadvertently.

Figure h

The right trapezius rotational muscle flap was used to completely cover the posterior instrumentation.

Post-operative neurological examination showed expected weakness of the left wrist flexion, left hand fingers flexion, adduction and abduction (all power grade 0/5). The right upper limb and bilateral lower limbs showed no neurological deficit. The left wrist flexion power improved to grade 3/5 after two months. There was mild left vocal cord palsy and mild Horner syndrome which both resolved in short course.

The final histopathology findings of the tumor specimen were compatible with the previous biopsy result, showing high grade osteosarcoma. There was no tumor necrosis seen (only half cycle of neoadjuvant chemotherapy was given due to intolerance). The specimen margin was close over the left 1st intercostal space soft tissue, otherwise the margin was clear. Chemotherapy was started at around 1 month after the operation. The patient declined further chemotherapy after 2 courses in view of repeated vomiting. In view of the close margin and incomplete chemotherapy, radiotherapy was offered by oncologist and declined by the patient.  

At the time when this paper was written, it was around 5 years after the en bloc excision. This lady could cope well with her full-time work and her daily life. There was residual pain and numbness over the left palm, which was well tolerated. Multiple CT scans and MRI were done targeting the operative site and all of them showed no tumor recurrence, with the latest MRI done at 48 months after the operation. Multiple bone scans and CT scans of the thorax and abdomen also showed no evidence of distant metastasis. In view of her disease-free status and likely plateaued neurological improvement, left upper limb reconstruction e.g tendon transfer was offered, and this lady was taking this option into consideration.

Discussion

This is a rare presentation of spinal osteosarcoma. Osteosarcoma usually presents with a bimodal distribution with the younger group peaking in adolescence but this lady was diagnosed with osteosarcoma at the age of 28. Secondly thoracic spinal osteosarcoma is much less common than the lumbosacral region one (12.5-22.7% vs >70%). Thirdly, the incidental finding of this spinal osteosarcoma makes its presentation even more atypical as most cases of spinal osteosarcoma were presented with pain and / or neurological deficit.

We believe that our case brings two future implications. Firstly, the colored 3D-printed model played a pivotal role in pre-operative planning and intra-operative guidance. Exposure over the left side was very limited in order to keep the tumor en bloc, thus the ligation of left C8-T2 nerve roots from the right side was very technically demanding. The 3D-printed model helped with delineating the tumor extend and its relationship with adjacent critical structures. In recent years, the use of 3D-printed model was shown to help with operative planning of complex spinal surgery and also patient’s understanding of the surgery [20, 21]. The model also helped with the communication among the cardiothoracic and vascular surgeons and us, echoing with literature reporting how 3D-printed model helped with inter-specialty communication [22]. In the recent one or two decades, different authors have tried to use navigation system for spinal tumor identification and excision. However, there is a significant learning curve and the use of navigation system is not without error [23, 24]. In the future, there will be a large potential to study on how intraoperative navigation guidance system, with the 3D model and continuous improving robotics, can help with the accuracy and safety of spinal tumor excision [24, 25].

Secondly, there was gradual kyphosis at C3/4 junction in our case. During our literature search, complications of spinal tumor excision were well reported, but few discussed about junctional problem after posterior instrumentation. In our case, posterior spinal instrumentation was performed from C4 to T5 level and there was gradual kyphosis at C3/4 junction (similar problem was not noticed at T5/6 junction). Clinically there was some stiffness of the neck with no pain nor tenderness. It was proposed that the C3/4 kyphosis was due to a significant amount of left paraspinal muscle excised in order to achieve adequate soft tissue margin. The right rotational trapezius flap was mainly performed for coverage of the instrumentation but not to provide strength for extending the cervical spine. Other possible options may include extending the posterior instrumentation proximally with occipitocervical fusion. However, likely more limitation in neck movement is expected for occipitocervical fusion. Literatures have shown multiple options of posterior trunk local flap reconstruction to protect the spinal cord, avoid leakage of the cerebrospinal fluid, provide long term coverage of the posterior instrumentation and lowered the risk of post-operative wound complications [26, 27, 28]. Nonetheless, none of the flap reconstruction is expected to provide adequate strength for cervical spine extension. Further study is required to explore options in preventing cervical kyphosis in spinal tumor excision with large amount of relevant paraspinal muscle excised.

Figure i

Post-operative cervical spine xray showing the C3/4 kyphosis.

Conclusion

This is a case of atypically presented T1 osteosarcoma which was treated with an en bloc excision. Five years after the operation, this lady enjoyed a disease-free survival with relatively good functional outcome. This case shows that en bloc excision should be offered to spinal osteosarcoma patients who are surgically fit, echoing with multiple literatures aforementioned in this paper. Relevant surgical complications and possible post-operative functional deficit should also be discussed. It would worth further study to see if other technology advancement can make more spinal tumor excision possible, with less complications and shorter operative time.