1

Introduction

Numerous materials have been described for the repair of tegmen defects. As long as the gap is reconstructed in two or more layers with different substances, recurrence of cerebrospinal fluid leak is uncommon . One material that is used is bone dust collected during the electrical drilling of the cranium for access to the defect. Bone dust also is referred to as “bone paté” in the literature . In this report we describe the use of cranial particulate bone graft to reconstruct the tegmen. After mixing particulate graft with blood, a bone paté is made which is grossly similar to the paté formed using bone dust. However, clinical and experimental evidence has shown that particulate graft is superior to bone dust for repair of full-thickness osseous defects.

2

Case report

A 43 year-old male presented with a 2 year history of left sided conductive hearing loss, a middle ear effusion, and a retracted tympanic membrane. Following myringotomy, he developed cerebrospinal fluid otorrhea and meningitis. Imaging confirmed a tegmen defect, and he underwent a transmastoid repair. A Hudson brace with a 16 mm D’Errico bit was used to drill over the mastoidectomy site, and particulate bone graft was harvested as previously described ( Fig. 1 ) . The graft was collected and mixed with blood to form a bone paté. The graft was placed intracranially in contact with the dura. The repair was reinforced using conchal cartilage, temporalis fascia, and hydroxyapatite cement. An intraoperative lumbar drain was removed at the end of the procedure. On postoperative day 4 a head CT that was negative for intracranial causes for postural headaches illustrated the reconstructed tegmen ( Fig. 2 ).

Cranial particulate bone graft harvested with a Hudson brace and 16 mm D’Errico bit.

(Left) Preoperative CT appearance of tegmen defects. (Right) Reconstructed tegmen on postoperative day 4.

2

Case report

A 43 year-old male presented with a 2 year history of left sided conductive hearing loss, a middle ear effusion, and a retracted tympanic membrane. Following myringotomy, he developed cerebrospinal fluid otorrhea and meningitis. Imaging confirmed a tegmen defect, and he underwent a transmastoid repair. A Hudson brace with a 16 mm D’Errico bit was used to drill over the mastoidectomy site, and particulate bone graft was harvested as previously described ( Fig. 1 ) . The graft was collected and mixed with blood to form a bone paté. The graft was placed intracranially in contact with the dura. The repair was reinforced using conchal cartilage, temporalis fascia, and hydroxyapatite cement. An intraoperative lumbar drain was removed at the end of the procedure. On postoperative day 4 a head CT that was negative for intracranial causes for postural headaches illustrated the reconstructed tegmen ( Fig. 2 ).

Cranial particulate bone graft harvested with a Hudson brace and 16 mm D’Errico bit.

(Left) Preoperative CT appearance of tegmen defects. (Right) Reconstructed tegmen on postoperative day 4.

3

Discussion

Transmastoid and/or middle cranial fossa approaches are used to repair cerebrospinal fluid leaks from temporal bone tegmen defects. Numerous materials have been described to reconstruct the gap in the tegmen (e.g., acellular dermis, adipose, bone wax, carbonated calcium phosphate, cartilage, collagen matrix, fascia, fibrin glue, gelfoam, hydroxyapatite, oxycel, mesh, muscle split cranial bone, titanium). Regardless of the type of surgical approach and substance used, recurrence of the cerebrospinal fluid leak is uncommon as long as the tegmen is repaired with multiple layers of different materials . One substance that has been used commonly to reconstruct holes in the tegmen is bone dust collected from a high speed burr during the initial mastoidectomy or craniotomy . The autologous bone dust then is typically mixed with blood, and/or fibrin glue to form a paste, before it is used to fill the bony defect.

Although bone dust has been reported to be efficacious for the repair of tegmen defects, it has always been used with another substance (i.e., carbonated calcium phosphate, cartilage, duragen, fascia, muscle, split cranial bone) . In contrast, when bone dust has been used alone to repair critical size calvarial gaps it does not ossify clinically or experimentally . Because the smallest dimension of a bone dust particle is less than 6 μm, it undergoes phagocytosis by macrophages and thus resorbs . Bone dust particles are also injured by heat from the high-speed burr which results in minimal numbers of viable cells and osteoblasts . Small, acellular bone dust does not have significant biological activity when used to fill osseous cranial defects .

In contrast to bone dust, cranial particulate bone graft is harvested with a hand-driven bit and ossifies cranial defects when used alone . The bit used to procure particulate graft is large, and thus the pieces of bone are more resistant to resorption . In addition, the low-speed harvest does not cause thermal injury, and thus the graft contains viable osteoblasts able to produce new bone . The graft forms bone as thick as the surrounding cranium, and even develops a diploic space . The donor sites are less than critical size, and thus re-ossify and can be used again to harvest additional bone graft (reparative osteogenesis) that also ossifies cranial defects .

Cranial particulate bone contains corticocancellous material and heals by osteogenesis (similar to cancellous bone graft), rather than by osteoconduction (split cranial graft), or osteoinduction (demineralized bone graft, bone morphogenetic protein) . Because particulate bone graft behaves similarly to cancellous bone graft, it requires vascularization to produce new bone and resist absorption . Consequently, the graft should be applied to a vascularized area, like the dura, to survive.

After harvesting particulate bone graft it is mixed with blood and positioned in contact with the dura. Fibrin glue may be placed over the graft to secure it, and this does not prevent vascularization or efficacy of material . We do not advocate mixing the graft with saline, antibiotic irrigation, or iodine because these solutions may injure cells in the graft. Particulate bone graft mixed with blood gives a bone paté, as has been described for bone dust. This bone paté is a particularly useful component of tegmen repair because it is easy to use, pliable, and can be molded to fill areas of deficient bone . These same principles of particulate bone grafting may be applicable to mastoid obliteration and repair of other temporal bone defects.