| disease | Skull Osteomyelitis |
| alias | Osteomyelitis of the Skull |
Traumatic cranial osteomyelitis is often caused by open craniocerebral injuries, especially severely contaminated gunshot wounds, or prolonged exposure of the skull due to scalp defects or necrosis. Occasionally, it may result from hematogenous infection. The scope of cranial osteomyelitis can be limited to a single skull bone or extend beyond sutures to involve multiple bones. In some cases, retrograde thrombophlebitis may spread the infection from beneath the periosteum or outside the dura mater into the intracranial space, leading to epidural empyema, subdural empyema, and/or brain abscess.
bubble_chart Clinical Manifestations
Acute osteomyelitis of the cranial vault often presents with scalp edema, pain, and local tenderness. When the infection spreads beneath the outer table periosteum, a Pott's puffy tumor may develop. Chronic cranial osteomyelitis typically manifests as a persistent sinus, recurrent ulceration with pus discharge, and occasionally the expulsion of sequestrated bone fragments.
Early-stage skull osteomyelitis is easily overlooked, and X-ray images only show obvious decalcification and destruction signs 2-3 weeks after infection. Chronic osteomyelitis is more clearly visible on X-rays, displaying moth-eaten, uneven bone destruction areas, sometimes with dense, patchy sequestrum images. In long-standing chronic skull osteomyelitis, bone sclerosis and hyperplasia may appear around the destruction area, making X-ray plain films sufficient for diagnosis.
bubble_chart Treatment Measures
The treatment of skull osteomyelitis should include surgical removal of necrotic and avascular bone while administering antimicrobial therapy, as relying solely on anti-infection treatment is ineffective.
Surgical method: The procedure is performed under local or general anesthesia. A linear or "S"-shaped incision is made centered on the lesion or through the sinus, and the scalp is reflected from the inflamed skull. Infectious granulation tissue and dead bone are removed, and diseased bone is excised by drilling in the affected area. The infected skull bone, due to thrombosis of the diploic vessels, usually bleeds minimally. The affected bone is often porous and fragile, while the surrounding bone remains dense and hard. All diseased bone should be completely removed until normal diploë is exposed. Inflammatory granulation tissue and pus outside the dura mater should also be thoroughly curetted, typically exposing 0.5–1.0 cm of normal dura mater, but care must be taken not to perforate it. The wound is thoroughly irrigated with a solution containing gentamicin 1500 μ/ml, then the scalp is closed in layers with interrupted sutures, and a rubber drain is placed subcutaneously for 24 hours. In cases of acute infection, the incision may be loosely closed with a rubber drainage tube left in place for postoperative drainage, medication administration, and irrigation.(1) Epidural empyema
Osteomyelitis of the skull is more likely to be accompanied by epidural empyema, and occasionally it can also be caused by incomplete early debridement of open skull fractures, by which time the scalp wound has often healed. In the early stages, such patients often experience headache, fever, and drowsiness. When an abscess forms, symptoms of increased intracranial pressure and compression of local brain tissue often appear, such as hemiplegia, aphasia, or neurological deficit signs. CT scans may reveal a spindle-shaped image similar to that of an epidural hematoma, appearing as a low-density area in the early stages and gradually changing to an isodense or high-density shadow after a week. Due to inflammatory granulation hyperplasia in the dura mater of the lesion area, the inwardly convex dura mater can be significantly enhanced, presenting as a dense arc-shaped band, which is characteristic. If the infection is caused by gas-producing bacteria, a fluid level and gas may appear.
For epidural empyema near the superior sagittal sinus or lateral sinus, vigilance should be maintained for the occurrence of thrombophlebitis of the venous sinus. Generally, after surgical removal of the abscess, antibiotic treatment should continue for 3–4 weeks. Additionally, appropriate anticoagulant therapy should be given to prevent venous sinus thrombosis.
(2) Subdural empyema
Subdural empyema can occur after skull osteomyelitis or due to improper early management of penetrating craniocerebral injuries. In non-traumatic cases, it often results from severe paranasal sinusitis. Early-stage patients often exhibit symptoms such as headache, fever, and neck stiffness. Later, symptoms of increased intracranial pressure gradually appear, such as headache, vomiting, vision decline, and drowsiness, but they often lack localized signs, making misdiagnosis more likely. Sometimes, due to the large size of the subdural empyema compressing the cerebral hemisphere or cortical surface vein thrombosis, neurological dysfunction such as hemiplegia, aphasia, or hemianopia may also occur. Additionally, the chance of accompanying focal epilepsy is relatively high, reaching up to 30%. A definitive diagnosis relies on imaging examinations such as cerebral angiography, CT, and MRI. Cerebral angiography not only shows cortical blood vessels displaced away from the inner table of the skull but also reveals the capillary imaging of granulation tissue surrounding the abscess. On non-contrast CT scans, the early stage often shows a crescent-shaped low-density area close to the inner table of the skull, usually accompanied by extensive cerebral edema, encephalitis, white matter infarction, and significant midline structure displacement. Enhanced CT may show a clearly defined, uniformly thin band of enhancement. When accompanied by cortical vein thrombosis and encephalitis, localized gyral enhancement may appear. On MRI, in T1
The treatment of subdural empyema generally advocates the use of drilling, drainage, and irrigation methods. Specifically, holes are drilled at the center and slightly lower part of the empyema area, the dura mater is incised, pus is drained, and an 8F catheter is inserted for repeated slow irrigation with antibiotic solution. The catheter is then left in place for postoperative drainage, medication administration, and irrigation. If the subdural empyema is caused by skull osteomyelitis, the diseased bone should be removed according to the surgical methods for skull osteomyelitis, while drainage tubes are placed to remove pus and irrigate the abscess cavity.
