The Symptomatic Calcification and Ossification of the Ligamentum Flavum in the Spine: Our Experience and Review of the Literature

Abstract

Introduction: We report our experience regarding the clinical features and pathological findings of the calcification of the ligamentum flavum (CLF) and ossification of the ligamentum flavum (OLF) in the spine. In addition, we reviewed the previous studies on CLF and OLF to enhance the understanding of these conditions.

Materials and methods: We compared the clinical, radiological, and histopathological features of CLF and OLF.

Results: In CLF, a computed tomography (CT) scan showed egg-shaped or speck-like calcification in the ligamentum flavum. Magnetic resonance (MR) imaging demonstrated spinal cord compression due to a thickened ligamentum flavum, which appeared as a low-intensity mass. Pathological findings demonstrated fused islands of calcification resembling sand-like calcification. In OLF, CT showed beak-like ossification extending into the intervertebral foramen. MR imaging demonstrated spinal cord compression by a low-intensity mass. Pathological findings revealed laminar ossification of LF with chondrocytes near the calcification and laminar hyaline cartilage.

Conclusions: CLF and OLF appear to be distinct entities based on their clinical, neuroradiological, histopathological, and pathogenetic features. We suggest that the causes of CLF include both metabolic and dystrophic factors, while the pathogenesis of OLF is characterized by enchondral ossification induced by a genetic cascade triggered by shearing/tension stress.

Keywords: calcification of the ligamentum flavum; clinical feature; ossification of the ligamentum flavum; pathogenesis; radiological finding; surgical management.

Figure 1

Three-dimensional and two-dimensional CT images of CLF. Three-dimensionally reconstructed CT image showing changes after en-bloc expansive laminectomy and laminoplasty using basket-type titanium plates (arrows) (A) and axial image (B). Three-dimensionally reconstructed CT image showing changes after single-staged posterior decompression (asterisks) and posterior lateral fixation using lateral mass screws and rods (arrows) (C) and axial image (D).

Figure 2

Illustrations demonstrating laminectomy for OLF in the thoracic spine. After thinning the lamina (black cross), cranial, caudal, lateral, and midline garters were made by drilling (black asterisks) (A,A’). The OLF was carefully dissected from the dura matter and removed (black arrows) (B,B’).

Figure 3

Two-dimensional CT images of CLF. Two-dimensionally reconstructed CT scan axial image (A) and sagittal image (A’) CT scan demonstrating “egg shape” high-density mass contacting with laminae (arrows) and posterior osteo-spur at the C5/6 intervertebral level (black arrows). Two-dimensionally reconstructed CT scan axial image (B) and sagittal image (B’) demonstrating “diffuse and speck like” high-density mass contacting with laminae in ligamentum flavum (white arrows). Two-dimensionally reconstructed CT scan axial image (C) and sagittal image (C’) demonstrating “egg shape” high-density mass in ligamentum flavum on the left side in (C) and along the ligamentum flavum in (C’) (white arrows), ossification of posterior longitudinal ligament at the C4/5, 5/6 (white arrowheads), and listhesis at C3/4 intervertebral level. Two-dimensionally reconstructed CT scan axial image (D) and sagittal image (D’) demonstrating “multiple islands of speck like and egg shape” high-density mass in ligamentum flavum (arrows) and ossification of longitudinal ligament at C3/4 (white arrowhead).

Figure 4

MR images of CLF. MR T2-weighted axial images (A–D) and sagittal images (A’–D’) from the same patient showing low intensity (arrow heads).

Figure 5

Two-dimensional CT images of OLF. Two-dimensionally reconstructed CT scan sagittal images (A–D) image and axial image (A’–D’) showing beak-like ossification extended to intervertebral foramen (white arrows).

Figure 6

MR images of OLF. MR T1-weighted axial images (A–D) and T2-weighted axial images (A’–D’) demonstrating low-intensity mass in dorsal spinal canal compressing spinal cord (arrows) and high-intensity spots (white asterisks).

Figure 7

Histopathological findings of CLF in illustrative case. Ventral side of laminae with ligamentum flavum while in operation (A) showing the smooth surface of ligamentum flavum and easily removed ligamentum flavum from laminae. Ventral side of laminae with yellow ligament cut (B) demonstrating island of calcification and fusion of them and many sand-like calcifications. Hematoxylin–eosin (H&E) staining (original magnification: 10×, 40×) (Case 10) (C,D (the area of yellow box was enlarged)) showed islands of calcification and their fusion (black arrows). Chondrocytes and osteoblasts were not identified.

Figure 8

Histopathological findings of OLF in illustrative case. Hematoxylin and eosin (HE) stain × 4 picture (A) showing stratified calcium deposition standing in a line in yellow ligament attached to the dura mater (arrows) and group of chondrocytes (arrowheads). HE stain × 10 picture (B) showing stratified bony development (asterisks), hyaline cartilage (sharps), and osteoblasts in it (arrowheads). HE stain × 20 (C) showing chondrocytes near ossification (arrows), osteoblasts in ossification (arrowhead), and hyaline cartilage (sharps), which demonstrates chondral bone formation. HE stain high-magnification × 40 picture (C’) certifying chondrocytes. HE stain × 20 picture (D) showing ossification encroaches vertically to the dura matter (arrows). Chondrocytes were confirmed near ossification (arrowheads). Elastic fiber is intact (white asterisk), and chondral ossification grows, closing ossification of ligamentum flavum side. Alcian blue stain × 40 picture (D’) certifying chondrocytes in dura mater side.