4.20.5\ Pseudomeningoceles

Pseudomeningoceles represent contained cerebrospinal fluid leakage or herniation of the subarachnoid space through a defect in the dura. Pseudomeningoceles are common postsurgical complications, especially in the suboccipital region. On imaging, pseudomeningoceles appear as simple fluid collections that bulge into the scalp or posterior cervical soft tissues and communicate with the intracranial space (Fig. 4.60).

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Pseudomeningoceles often resolve spontaneously as the dura seals over time and cerebrospinal fluid absorption returns to normal. However, when these are persistent or the suture line is under excess tension, exploration, repair, and/or cerebrospinal fluid diversion can be considered. Persistent or enlarging cerebrospinal fluid collections near burr holes can sometimes reflect impairments in cerebrospinal fluid absorption, except in infants, where cerebrospinal fluid can be extruded while crying and can get trapped extracranially.

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Fig. 4.60  Suboccipital craniectomy pseudomeningocele. Axial CT image (a) shows a large fluid collection at the suboccipital craniectomy site (*). Axial T2–weighted (b)

and axial (c) and sagittal (d) T1-weighted MRI sequences show a fluid collection that follows cerebrospinal fluid signal intensity (*) at the suboccipital craniectomy site

4.20.6\ Pseudoaneurysm

Significant arterial injury resulting from retrosigmoid craniotomy is an uncommon incident. Significant injury of the scalp arteries from cranial surgery is uncommon, but can lead to pseudoaneurysms. Patients can present with a pulsatile

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mass that appears as a hyperattenuating collection in the scalp on CT (Fig. 4.61). Angiography is recommended to ascertain the presence of a pseudoaneurysm, which appears as an ovoid structure that enhances in parallel with the arteries. Pseudoaneurysms can resolve spontaneously but may be amenable to endovascular therapy.

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Fig. 4.61  Postoperative occipital artery pseudoaneurysm. Axial CT image (a) shows hemorrhage overlying the left retrosigmoid craniotomy site. CTA MIP image (b)

shows a large left occipital artery pseudoaneurysm (arrow). The pseudoaneurysm was subsequently coiled, as shown on a follow-up CT (c)

4.20.7\ Postoperative Infection

Infection is a serious complication of craniotomy, craniectomy, and cranioplasty that can occur in the subgaleal, extradural, or subdural spaces within the bone flap and surrounding the cranioplasty (Figs. 4.62 and 4.63). The incidence is generally 4.5–6%, but varies depending upon the type of material used. Staphylococcus aureus is the most common responsible organism. The appearance on CT is that of a fluid collection with peripheral enhancement. MRI may show restricted diffusion in the abscess. In addition, MR spectroscopy may show elevated lactate. Although systemic signs of infection can be mild, management consists of wound debridement, antibiotics, and removal of the cranioplasty. Progressive increase in size of the collection over time is a particularly suspicious finding. Osteomyelitis of bone flaps

comprises over 40% of all infectious complications following craniotomy. The vast majority of these cases are due to infection by Staphylococcus aureus. Infected bone flaps may either demonstrate areas of lucency or sclerosis on CT. These findings are not specific for osteomyelitis and can be seen in normal bone flaps. However, the presence of secondary changes, such as overlying sinus tracts, skin thickening, fat stranding, and adjacent fluid collections, should raise the suspicion of an infected bone flap. MRI can demonstrate increased T2 signal and decreased T1 signal intensity within the infected bone flap marrow. In addition, predisposing factors include communication with the sinuses, multiple surgeries, long intraoperative times, and surgery for preexisting intracranial infection. Treatment of bone flap osteomyelitis ranges from conservative management to bone flap removal.

Fig. 4.62  Infected craniotomy bed. Axial T2 (a), axial T1 (b), post-contrast axial (c), and coronal (d) T1 show irregular fluid collections with rim enhancement in the left parietal lobe and scalp overlying the craniotomy. There is

restricted diffusion within the intraparenchymal abscess on DWI (e) and ADC map (f) and abnormal signal in the craniotomy flap due to osteomyelitis