Indolent enhancing spinal lesions mimicking spinal metastasis in pediatric patients with malignant primary brain tumors

Abstract

Spinal metastasis from malignant primary brain tumors (MPBTs) in pediatric patients is rare and often appears as enhancing lesions on MRI. However, some indolent enhancing spinal lesions (IESLs) resulting from previous treatment mimic metastasis on MRI, leading to unnecessary investigation and treatment. In 2005-2020, we retrospectively enrolled 12 pediatric/young patients with clinical impression of spinal metastasis and pathological diagnosis of their spinal lesions. Three patients had MPBT with IESL, and 9 patients had malignant tumors with metastases. The histopathologic diagnosis of IESL was unremarkable marrow change. We evaluated their MRI, CT, and bone scan findings. The following imaging findings of IESL vs. spinal metastasis were noted: (1) IESLs appeared round/ovoid (3/3, 100%), whereas spinal metastasis appeared irregular (9/9, 100%) (P = 0.005); (2) target-shaped enhancement was noted in (3/3, 100%) vs. (0/9, 0%) of cases, respectively (P = 0.005); (3) pathologic fracture of the vertebral body was noted in (1/3, 33.3%) vs. (9/9, 100%) of cases, respectively (P = 0.045); (4) expansile vertebral shape was noted in (0/3, 0%) vs. (9/9, 100%) of cases, respectively (P = 0.005); (5) obliteration of the basivertebral vein was noted in (0/3, 0%) vs. (9/9, 100%) of cases, respectively (P = 0.005); and (6) osteoblastic change on CT was noted in (3/3, 100%) vs. (2/9, 22.2%) of cases, respectively (P = 0.034). IESL in pediatric patients with MPBT can be differentiated from metastasis based on their imaging characteristics. We suggest close follow-up rather than aggressive investigation and treatment for IESL.

Figure 1

Indolent enhancing spinal lesion (IESL)—Case 1. An 11-year-old girl with anaplastic astrocytoma (2016 WHO grade III) over the right thalamus (a,b) was treated with partial tumor removal, radiotherapy, and chemotherapy. Four months after the surgery, sagittal contrast-enhanced T1WI revealed diffuse leptomeningeal seeding and multiple enhancing lesions over the whole spine (c,d). Target enhancement (d, arrow), ring enhancement (c, white arrow) and corner involvement (c, black arrow) were present. In the follow-up MRI 6 months after brain tumor surgery, sagittal contrast-enhanced T1WI of the cervical to middle thoracic spine revealed progression of the lesions (e). A target-enhancing pattern was specified at the T10 level (d,e, white arrow; magnified in f), which appeared hypointense on T2WI (g, white arrow). Coexisting lesions with ring enhancement on T1WI (e, black arrow) and hyperintensity with a “double line sign” on T2WI were also noted (g, black arrow). The T10 target-enhancing lesion on axial contrast-enhanced T1WI (h) revealed osteoblastic changes on CT scan (i). The first CT-guided biopsy disclosed no histologic evidence of malignancy (j). One week later, the second CT-guided biopsy revealed hypocellular marrow tissue and bone dust (H&E staining) (k).

Figure 2

Indolent enhancing spinal lesion (IESL)—Case 2. An 11-year-old boy with medulloblastoma of the cerebellum (a,b) had undergone surgical resection and chemoradiotherapy. Sagittal contrast-enhanced T1WI revealed multiple enhancing foci in the cervical to thoracic spine 15 months after the diagnosis (c,d). Focal leptomeningeal seeding was noted at the C1 level (c, black arrow). In the follow-up MRI 33 months after brain tumor surgery, sagittal contrast-enhanced T1WI revealed significantly progressive changes in the lesion at vertebrae T11 with a target enhancement pattern (e, arrow). The lesion exhibited hypointensity on T1WI (f) and hypointensity on T2WI (g). Several enhancing lesions were also present at the temperoparietal skull bone of the brain MRI (h). On axial images, the T11 lesion had strong enhancement on contrast-enhanced MRI T1WI (i) and osteoblastic changes on the CT scan (j). CT-guided biopsy of the T11 lesion showed mild marrow fibrosis, adipose tissue filled in the marrow spaces, and scattered hematopoietic cells (H&E staining) (k,l).

Figure 3

Indolent enhancing spinal lesion (IESL)—Case 3. An 11-year-old boy had a germ cell tumor over the thalamus to the hypothalamus (a,b). He had completed radiotherapy and chemotherapy. Seventeen years after the initial diagnosis, follow-up spinal MRI revealed enhancing lesions in the lumbosacral region on sagittal contrast-enhanced T1WI (c, arrow). Progressive changes in the lesions over the whole spine were observed one year later (d–f). These lesions appeared well enhanced on contrast-enhanced T1WI (d,g) with hypointensity on T1WI (e) and T2WI (f,h). A target enhancement pattern was also identified (d, black arrow). CT-guided biopsy of the L4 lesion revealed nearly normal hematopoiesis (H&E staining) (i,j).

Figure 4

A case of spinal metastasis (SM). A 15-year-old male with synovial sarcoma over the left knee and pulmonary metastasis had undergone tumor resection and radiotherapy. Twenty-two months after the initial diagnosis, follow-up chest CT revealed an osteolytic lesion at the T7 spine with partial collapse of the vertebral body (a). MRI revealed hypointensity on T1WI (b), strong enhancement on contrast-enhanced T1WI (c), and isointensity on T2WI (d). Tc99m bone scan revealed avid uptake over T7 (e, arrow). The T7 lesion appeared osteolytic on axial CT image (f). Axial contrast-enhanced MRI T1WI at the T7 level revealed enhancing lesions with expansile changes, paraspinal soft tissue (g, arrow), epidural soft tissue (g, arrowhead), and obliteration of the basivertebral vein. Bone metastasis was histologically proven by T7 corpectomy (H&E staining) (h).

Figure 5

Indolent enhancing spinal lesion versus spinal metastasis. Comparison of the image characteristics of IESL and SM. IESLs tend to (1) be round/ovoid and well-defined; (2) exhibit an osteoblastic appearance on CT; (3) display target-shaped enhancement on contrast-enhanced MRI; (4) have preserved basivertebral veins; and (5) lack vertebral pathological fractures, paraspinal soft tissue, and expansile vertebral shapes.