Post-operative brain imaging may be deceptively simple or overwhelming depending on the baseline pathology, surgical techniques and variety of features.

A structured outside-in (or inside-out based on preference) approach could be a reliable tool in identifying all potential imaging findings and complications.

A proposed layered approach starting from the outside includes evaluation of the scalp, skull, extraaxial compartments, surgical cavity, brain parenchyma (intraaxial compartment), mass effect markers, ventricular system, vessels, intracranial devices and other extracranial incidental findings.

Fig 1: NECT, annotated. Proposed layered approach of post-operative brain and skull. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

0. Clinical information

Before delving into the post-operative brain imaging puzzle, it is important to acknowledge all relevant clinical information, including patient history, clinical status, exam indication, surgical intervention performed and prior imaging.

1. Scalp

Expected findings: tumefaction, subgaleal post-operative collection.

Subgaleal collection: adjacent to the surgical site, can extend around the skull crossing suture lines; usually mixed density – mostly fluid and air densities with small foci of recent hemorrhagic densities.

Complications: infection; hemorrhage; hygroma; external brain tamponade [1].

2. Skull

Types of surgical approaches:

• Burr holes – well defined round defects of the skull vault; several purposes: device insertion, biopsy, drainage, precursor for craniotomy
• Craniotomies – surgical removal of a portion of the skull with the bone flap repositioned after the procedure; six standard types (pterional, subtemporal, anterior parasagittal, posterior parasagittal, median suboccipital and lateral suboccipital) with variations
  

  Fig 2: CT-VR. Different types of craniotomies: A - Pterional; B - Subtemporal; C – Anterior parasagittal; D – lateral suboccipital. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024
• Craniectomies – surgical removal of a portion of the skull without subsequent replacement, the intracranial structures are covered by a skin flap (meningo-galeal layer); several purposes – decompression, excision of a tumor with bone invasion, infection removal
  

  Fig 3: A - CT-VR. Right sided hemicraniectomy. B – NECT. Meningo-galeal layer (skin flap) covering the intracranial contents (red arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024
• Cranioplasties – surgical reconstruction of a skull defect; various techniques and materials (titanium mesh, acrylic, bone grafts) [1,2]
  

  Fig 4: A (NECT, bone window) and B (CT-VR). Left titanium mesh cranioplasty. C (NECT, bone window) and D (CT-VR). Right acrylic cranioplasty. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Checklist: bone flap/cranioplasty/skin flap integrity and positioning.

Complications: displacement, infections, fractures, sinking skin flap [1-3].

Fig 5: NECT. Right sided craniectomy with sinking skin flap in the frontal region (white arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

3. Extraaxial compartments

Expected findings: mixed density post-operative collections, pneumocephalus.

Fig 6: NECT. Small extradural post-op collection (white arrow) subjacent to the left pterional bone flap. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Complications: hygromas, hemorrhage, infections, CSF leaks.

Fig 7: NECT. Left frontal post-operative acute subdural hematoma (red arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 8: NECT. Left craniectomy with subgaleal and extradural acute hematoma. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 9: NECT. Median subccipital decompressive craniectomy with CSF leak and large pseudomeningocele formation. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

3.1. Pneumocephalus

Location: extraaxial, intraaxial (surgical cavity) and/or intraventricular; most often it occurs in the subdural space overlying the frontal or temporal lobes.

Checklist: quantitative assessment, location.

Complications: larger volumes may compress underlying brain parenchyma leading to tension pneumocephalus, with life-threatening potential; however, diagnosis should be made only if there is associated clinical deterioration; CT appearances include “peaking” and “mount Fuji” signs [2].

Fig 10: NECT (lung/bone window). A – Extraaxial (small amount) and intraventricular (moderate amount) of post-operative pneumocephalus. B – Right anterior frontal tension pneumocephalus with “peaking” sign (white arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

4. Surgical cavity

Expected findings: mixed densities (air, CSF and blood products).

Fig 11: NECT. Normal immediate post-operative appearance of the surgical cavity with mostly fluid density (white star), small amount of air (blue arrow) and some peripheral foci of recent hemorrhagic densities (red arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 12: MRI (A – T2WI, B – FLAIR, C – SWI, D – T1WI). Normal appearance of a recent surgical cavity with a mixture of subacute blood products, necrotic material and CSF, with a peripheral hemosiderin rim. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Complications: hemorrhage, infection.

Fig 13: NECT. Acute hematoma (white arrow) in sellar and suprasellar surgical cavity (macroadenoma resection). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Pericavitary parenchyma: edema (preexisting or new), residual tumor, long-term effects (retraction, gliosis).

Fig 14: CECT. Right cerebellar-pontine angle decompression surgery (blue circle). Large residual tumor (red circle) extending into the right pons, cavernous sinus (A) and through foramen ovale into the parapharyngeal space, along the mandibular division (V3) of the trigeminal nerve (B). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

5. Brain parenchyma

• Ischemia – either newly onset or evolving; most frequently encountered after aneurysm treatment, in significant brain herniations and vascular compressions. 
• Hemorrhage – either newly onset, evolving (e.g. after a traumatic brain injury) or hemorrhagic transformation of an infarct.
• Cerebral edema – both vasogenic and cytotoxic types can coexist, and their extent is dependent on preexisting factors (e.g. peritumoral edema), context (e.g. traumatic brain injury) and new or developing lesions (hemorrhage, ischemia).

A 5 (+1) point scale was developed to better quantify the extent of the edematous changes:

0 – No cerebral edema

1 – Focal edema (1 lobe)

2 – Unilateral edema (>1 lobe)

3 – Bilateral edema

4 – Global edema (sulcal effacement)

5 – Global edema (sulcal and basal cisterns effacement)

1 additional point for grades 1-4: mass lesion with surrounding edema with midline shift >5 mm [4].

Fig 15: NECT. Acute stroke in bilateral anterior cerebral artery territory (A) with subsequent hemorrhagic transformation (B) (red circle). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 16: A – CT-Angiography. Large left M2 segment aneurysm. B – NECT (bone window). Surgical clipping of the aneurysm and pterional craniectomy. C – NECT. Acute left fronto-insular stroke with mass effect. D – NECT. Subacute to chronic phase with regression of mass effect. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

6. Mass effect markers and herniation syndromes

6.1. Mass effect markers

Midline shift – standardized measurement of the lateral displacement of midline structures (most commonly used landmark is the septum pellucidum); more than 5 mm is considered clinically significant.

Fig 17: A – NECT. Large right hematoma with significant midline shift to the left. B - NECT. Slight regression of the midline shift after hematoma evacuation. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Other signs: sulci crowding/effacement, ventricular volumetric changes, bone/skin flap elevation [3-5].

Fig 18: NECT. Sulcal effacement on the left side (red arrow) compared to normal sulci on the right (blue arrow) due to cerebral edema. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 19: NECT. Left lateral ventricle compression (red arrow) due to mass effect. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

6.2. Herniation syndromes

Intracranial: subfalcine, transtentorial, tonsillar, transalar and paradoxical [2,5]

Paradoxical hernia: uncommon complication in decompressive craniectomy in patients who undergo CSF drainage [2]

Extracranial: through skull defect post-craniectomy/craniotomy. 

Checklist: evolution in time – new, developing or subsiding.

Table 1: Hernia types and associated displaced structures. Adapted from [3] and [5].

Fig 20: NECT. Progressive extracranial herniation through craniectomy defect (red arrows). Small subgaleal and extradural hematoma on Day 2 (blue arrow) which subsequently resolved. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 21: NECT. A – Massive acute subarachnoid and intraventricular hemorrhage (with active bleeding swirl sign – gold star) due to internal carotid artery aneurysm rupture (not shown). B, C and D – increasing cerebral edema and intracranial pressure with progressive displacement of the left pterional bone flap (red arrow) with extracranial herniation of brain parenchyma through the skull defect. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

7. Ventricular system

Checklist: size, volumetric changes in time, ventricular foramina patency, periventricular parenchyma, contents.

Complications: intraventricular hemorrhage, ventriculitis, hydrocephalus - preexisting, new or developing.

Fig 22: NECT. A – Acute intraventricular hemorrhage with foramen of Monro obstruction (red arrow). B – Acute intraventricular and subarachnoid hemorrhage with aqueduct of Sylvius (red star), obex (red arrow) and perimedullary cisterns obstructions. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

8. Vessels

Checklist: anatomy, patency, caliber, surgical clips, endovascular stents.

Complications: aneurysms (rupture, residual post-clipping), thrombosis, occlusion, contrast extravasation, associated parenchymal changes (infarctions/hemorrhages)

Fig 23: CT-A. A – Large M1 bifurcation aneurysm of the right middle cerebral artery. B – Post-surgical clipping residual aneurysm (white arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 24: A – CECT (bone window). Right lateral suboccipital craniotomy for cerebellar-pontine angle tumor resection. B – NECT. Spontaneously hyperdense right transverse sinus (blue arrow) with small cerebellar parenchymal infarction (white arrow). C – NECT and D – CECT. Lack of enhancement of right transverse sinus consistent with acute thrombosis. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

9. Intracranial devices

A wide variety of devices can be deployed intracranially – pressure monitors, ventricular shunts (ventriculo-peritoneal, ventriculo-atrial etc.), external ventricular drains, brain stimulators (thalamic, occipital).

Checklist: positioning – in the case of ventricular shunts, both extremities should be verified (intracranial and intraperitoneal/intraatrial); functionality – by using indirect imaging markers (ventricular volumetry)

Complications: hemorrhage, malposition, obstruction, under or overshunting, intracranial hypotension.

Fig 25: NECT. External ventricular drain with peritubular edema and hemorrhage with intraventricular hemorrhage. Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Fig 26: NECT. Patient with long term ventriculo-peritoneal shunt. Several imaging signs suggestive of chronic over-shunting and intracranial hypotension: A – Bilateral subdural hygromas (blue arrows) and distended dural sinuses (red arrow); B – Skull hyperostosis (white arrow); C – Distended vertebral epidural venous plexus with possible cord compression (orange arrow); D – Thinned optic nerve sheath (green arrow). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

10. Incidental findings

Usually found in the extracranial compartments, outside the central zone of interest – e.g. orbits, sinuses, cervical spaces. Findings can include incidental lesions, tumors, collections, misplaced devices/catheters and many others, some of which are clinically significant for patient management.

Fig 27: A – CECT. Complex cystic right submandibular mass (white arrow) (metastatic necrotic adenopathy from oro/hypopharynx carcinoma). B – Spinal tumors (blue arrows) and right intraforaminal tumor (red arrow) – most likely spinal ependymomas and meningiomas/schwannoma (in the context of neurofibromatosis type 2). C – Right internal jugular vein intravascular tubular structure (red circle) which corresponds on the CT scout image (D) to a malpositioned central venous catheter (blue arrowheads). Image source: Department of Radiology, Cluj-Napoca County Clinical Emergency Hospital/ Romania 2024

Table 2 presents a summary of the complicated layered brickwork of the post-operative brain imaging findings.

Table 2: A brick-like layered summary of complications mentioned in this poster.