Lung Abscess versus Empyema

Coronal reformatted chest CT images show a lesion in the right upper lobe with internal air-filled cavity, thick irregular wall (green arrowheads) and another lesion in the left lower lung with internal fluid, thin wall (yellow arrowhead) and adjacent compression of the lung tissue (yellow arrows and box). The right upper lobe lesion is an abscess and the left lower lung lesion is an empyema.

Lung Abscess

• Localized suppuration with destruction of lung parenchyma
• Round, thick-walled cavity in areas of destroyed lung
• Typically irregular wall, irregular luminal margin and exterior surfaces
• Usually treated by prolonged antibiotics and postural drainage

Empyema

• Pus in the pleural cavity
• "Split pleural" sign: separation of uniformly thickened visceral pleura from parietal pleura
• Compression of uninvolved lung
• Usually require early tube drainage

Differentiating the Two

• Most specific signs: "split pleura" sign of empyema, compression of adjacent uninvolved lung in empyema
• Helpful signs: at least one wall of empyema is thin, uniform and smooth on both luminal margin and exterior surface
• Less reliable sign: size, shape (oval vs round), chest wall angle (obtuse vs acute)

Reference:

Stark DD, Federle MP, Goodman PC, et al. Differentiating lung abscess and empyema: radiography and computed tomography. AJR 1983;141:163-167.

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Clay Shoveler Fracture

A lateral cervical spine radiograph and sagittal-reformatted CT image show an oblique fracture of the C7 vertebra with slight displacement. There is no extension to the lamina or facet joint on axial CT (not shown).

Clay Shoveler Fracture

• Avulsion, hyperflexion injury of the spinous process of C6, C7 or T1
• Typically oblique in orientation
• Due to abrupt flexion of the head and neck against tensed posterior neck ligaments
• First described in Australian clay miners who attempted to throw a shovel full of clay from the mine floor but the shovel stuck in the clay, causing abrupt hyperflexion of the neck
• Mechanically and neurologically stable unless it extends into the lamina. Also should look for facet joint injury or dislocation

Reference:

Schwartz ED, Flanders AE. Spinal trauma: imaging, diagnosis and management, 2007, 1st ed.

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Malignant Otitis Externa

An Axial CT image of an 82-year-old diabetic man shows marked thickening of the right pinna (arrowhead) and external auditory canal (arrows) without extension to the skull base or evidence of mastoiditis.

Facts: Malignant Otitis Externa

• Severe infection of the external auditory canal (EAC) and skull base
• Elderly diabetics and immunocompromised patients
• Most common organism = P. aeruginosa
• Extension into deep structures or chronic osteomyelitis may occur without signs on local examination
• Potential complications: osteomyelitis of the temporomandibular joint, sigmoid sinus thrombosis, meningitis, optic neuritis
• Biopsy usually required to exclude carcinoma

Staging

1. Stage 1 = confined to EAC and/or facial nerve paralysis
2. Stage 2 = osteitis of the skull base and/or multiple cranial nerve involvement
3. Stage 3 = meninges or brain involvement

Imaging

• CT commonly used to define location, extent of disease.
• MRI may complement CT in cases with cranial nerve, brain involvement
• Imaging monitoring of diseases may be done with bone scan and/or gallium scan

Reference:

Okpala NCE, Siraj QH, Nilssen E, Pringle M. Radiological and radionuclide investigation of malignant otitis externa. J Laryngol Otol 2005;119:71-75.

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Diffuse Axonal Injury

Figure 1: Axial FLAIR MR image shows several high signal foci (arrows and arrowhead) in the gray-white junction of the left frontal lobe in this patient status post closed head trauma (day 1 after trauma). Similar lesions are also seen in the basal ganglia.
Figure 2: Axial GRE MR (susceptibility) image shows two foci demonstrating susceptibility artifact (dark signal intensity, arrows) representing blood products. Another focus (arrowhead) shows minimal to no susceptibility, which may represent a non-hemorrhagic lesion.

Diffuse Axonal Injuries (DAI)

• One of the most common primary traumatic brain injuries in patients with severe head trauma (up to 48% in one series)
• Specific pattern of post traumatic diffuse degeneration of the white matter, attributed to prior shearing injury of the white matter
• Impaired consciousness is usually greater in patients with DAI than in patients without DAI
• Frequent cause of poor clinical outcome in patient with head injuries

Pathology

• Only some lesions are evident on autopsy as small, focal traumatic lesions.
• Many can be visualized only on microscopic examination as multiple axonal retraction balls (pathologic hallmark) and perivascular hemorrhage
• With time, there are microglial and astrocytic reactive changes, endothelial proliferation and accumulation of hemosiderin-laden macrophages at the site of axon disruption
• Three common locations: lobar white matter, corpus callosum, dorsolateral brainstem

Imaging

• MRI much more sensitive than CT for detection and characterization of DAI lesions
• Multiple, small, deeply situated, elliptical lesions sparing the overlying cortex
• Lesions may be hemorrhagic or non-hemorrhagic (the latter is more common) (CT will easily overlook non-hemorrhagic lesion and small hemorrhagic petechial hemorrhage)
• High signal intensity on T2WI, FLAIR (FLAIR more sensitive)
• Dark signal intensity on susceptibility MR sequence (i.e. T2* GRE) of hemorrhagic lesions

References

1. Gentry LR. Imaging of closed head injury. Radiology 1994;191:1-17.

2. Parizel PM, Ozsarlak O, Van Goethem JW, et al. Imaging findings in diffuse axonal injury after closed head trauma. Eur Radiol 1998;8:960-965.

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Happy New Year 2010

It's 01.01.10!

Have a very Happy New Year from the RiTradiology Team!