To present a rare case of a cystic giant schwannoma of the sacrum mimicking aneurysmal bone cyst (ABC). A 54-year-old man visited our institute complaining left leg weakness and sensory change for several years. Magnetic resonance imaging revealed a large multilocular cystic mass with canal invasion and bone erosion confined to left S1 body. The lesion showed multiple septal enhancement without definite solid component. Initially the tumor was considered as ABC. The patient underwent grossly-total tumor resection with lumbosacral reconstruction via posterior approach. The tumor was proved to be a cystic schwannoma. The postoperative course was uneventful and the patient was relieved from preoperative symptoms. We present a rare case of pure cystic giant schwannoma confined to sacrum mimicking ABC. The surgical treatment is challenging due to the complex anatomy of the sacrum. Schwannoma should be considered in the differential diagnosis of osteolytic sacral cysts.
Spinal schwannoma are relatively common, accounting for 25% of all primary spinal tumors
The incidence of sacral schwannoma ranges from 1% to 5% of all spinal schwannomas and only about 50 cases are reported in the literature
Most schwannomas are solid or heterogenous-solid tumors and degenerative changes into hemorrhage, calcification, and fibrosis are rather common. However, cystic changes are very rare
The combination of giant sacral schwannoma with significant cystic component is extremely rare and only few cases have been reported in the literature
A 54-year-old man visited the outpatient clinic complaining tingling sensation and paresthesia of left lower limb for several years. His symptoms have been aggravated during the last several months and there has been no improvement after conservative cares. He had no history of previous trauma or constitutional symptoms. Neurologic examination revealed weakness of dorsiflexion and plantaflexion on the left foot with mild hypesthesia at the left S1 dermatome. Perineal and perianal sensations were also mildly decreased.
Plain radiograph showed an osteolytic lesion limited to left sacral ala sparing lumbar spine (
The initial preoperative diagnosis was ABC, with several radiologic clues such as the location of mass, which was presenting in sacrum and compromising the neural arch, near totally cystic nature and balloon-like expanslile remodeling of bone. Even fluid-fluid level was not revealed in the imaging studies, ABC was strongly suspected.
We underwent a grossly-total tumor resection with lumbosacral reconstruction via posterior approach. A well-defined, encapsulated, cystic mass was found in epidural space adherent to nerve sheath displacing sacral nerve roots peripherally. The borders of tumor was carefully identified and dissected to preserve capsule of the cystic component under operating microscope. Once pericapsular dissection was done, en-bloc tumor resection was followed and sacral nerve roots were successfully preserved under spontaneous and evoked electromyography monitoring (
After the operation, the patient was completely recovered from the preoperative symptoms without any neurologic deterioration (
The patient was discharged at 1 week after the operation without any complications. Outpatient clinic follow-up for 6 month showed no symptom recurrence and the patient was tolerable. Serial follow-up X-rays at 3 and 6 month after surgery showed no implant-related complications.
Sacral schwannomas are very rare etiology comprising less than 1% to 5% of all spinal schwannomas. Cagli et al.
Based on the classification system proposed by Sridhar et al.
The initial presenting symptoms are mild, non-specific and not until the tumor becomes large enough to displace nerve root peripherally that the patient experience pain or numbness. Axial back pain or radicular pain is the most common symptoms. Delayed presentation is common due to slow growing nature of the tumor and the surrounding anatomic environment is somewhat permissive. Moreover, most of the patients' are young and otherwise healthy and neurological deficits may be minimal despite of large mass size.
The presence of a predominantly cystic schwannoma in the lumbosacral region is rare. These cystic changes are likely attributable to mucinous degeneration, ischemic necrosis, intra-tumor hemorrhage, and the formation of microcysts. Purely cystic tumor is very unusual finding in the spinal schwannoma, although there are a few reports of dominant cystic component in other anatomic locations
The initial differential diagnosis should include relatively large, sacral bone-erosive masses such as abscess, chordoma, metastatic carcinoma, myeloma, giant cell tumor, ABC, chondrosarcoma, osteoblastoma, and schwannoma
ABC is a benign, tumor-like, highly vascular, locally aggressive and osteolytic lesion of unknown etiology. ABCs are known to have a predilection for the lumbar spine but in some clinical series sacrum was involved more than others
In our case, the initial diagnosis was ABC because of sacral location, typical ballooning with thin peripheral rim in plain film, multiloculated osteolytic lesions with septation on CT scan, pathologic fracture of upper S1 endplate and well defined peripheral rim with multiple internal septation on MR imaging. We did not perform conventional spinal angiography as it is not essential preoperative study for ABC and therefore considered too invasive. Although, usual fluid-fluid level was not present, both radiologist and neurosurgeons strongly suggested ABC as the first differential diagnosis. Cystic schwannoma should be considered as a differential diagnosis option when treating osteolytic sacral cysts suggestive of ABC.
Plain radiographs and CT scans demonstrate the bone destruction and are required to evaluate the spinal stability as most giant schwannomas arising within the spine grow to a large size and result in pedicle erosion, and widening of the neural foramen with occasional destruction of the vertebra bodies. In cases of cystic schwannomas, CT usually shows a non-specific, well defined lesion with low or mixed signal, rarely with areas of cystic necrotic centre
Definitive diagnosis is based on histological examinations. The histologic findings of cystic schwannoma do not seem to differ from classic schwannomas which consists of spindle-shaped cells with pale, eosinophilic cytoplasm arranged in 2 characteristic patterns : Antoni A (compact, hypercellular spindle cells in "palisading" organization) and Antoni B (hypocellular, pleomorphic cells with predominantly myxoid cytoplasm)
Complete excision is recommended for management of giant spinal schwannoma because partial resection has a risk of recurrence
Spinal stabilization is one of the important goals in the treatment of large sacral tumors with bony erosions. Kagaya et al.
The combination of giant sacral schwannoma with significant cystic component is extremely rare and only few cases have been reported in the literature
We present a rare case of pure cystic giant schwannoma confined to sacrum mimicking ABC. The surgical treatment is challenging due to the complex anatomy of the sacrum. A successful surgical outcome depends on early diagnosis and complete excision. Schwannoma should be considered in the differential diagnosis of osteolytic sacral cysts.
Simple radiograph shows "ballooning" of osteolytic lesion involving left sacral ala (black arrows) without lumbar spine involvement.
A : MR imaging shows 5.1×3.4×3.6 cm sized multiloculated cystic mass with bony expansion into left S1 body. Lt. S1 root compression is also seen. The mass is seen as homogenous hypointense signal on T1-weighted image and hyperintense signal on T2-weighted image. B : Multi-septated cystic rim enhancement with gadolinium contrast enhancement is noted but no definite solid portion was found.
Axial and sagittal CT scan reveal an intraosseous expensile mass involving left sacrum. Compression of the left S1 nerve root and displacement (arrowhead) of the left sacral nerves below S1 nerve is noted. Subtle pathologic fracture involving upper-endplate of S1 is also seen (arrow).
A : Intraoperative image of before tumor dissection (* : cystic tumor capsule, → : S1 nerve root). B : Intraoperative image of after complete tumor removal. C : Pathologic specimen of tumor cystic capsule.
Postoperative plain film. Lumbosacral reconstruction involving transpedicular screw fixation of L4-S1 and bilateral trans-iliac screws was done. Lt. S1 level was omitted due to pedicle invasion.
Postoperative enhanced MR imaging revealed complete resection of tumor.
Histopathology of tumor. A : Spindle-shaped cells with pale, eosinophilic cytoplasm arranged in 2 characteristic patterns : Antoni A and B (H&E, original magnification ×50). B : Several Verocay bodies with nuclear palisading (H&E, original magnification ×50).