OS ACROMIALE

UNFUSED ACCESSORY OSSIFICATION CENTRE OF ACROMION OF SCAPULA

 

 

There are normally 3 acromial ossification centers that fuse between 22 and 25 years of age.

An os acromiale results from the failure of 1 of these centers to fuse.

The anterior ossification center is termed the pre-acromion, the middle is the meso-acromion, and the posterior is the meta-acromion.

The basi-acromion forms the point of attachment of these 3 ossification centers to the scapula.

A number of subtypes of os acromiale have been described.

The most common variant is nonfusion between the meso- and meta-acromion.

The prevalence of os acromiale in radiographic and anatomic studies ranges between 1% and 15%.

An os acromiale can contribute to shoulder impingement symptoms.

Contraction of the deltoid muscle may pull the os acromiale downward, causing it to impinge on the rotator cuff.

Abnormal motion may lead to an osteophytic spur at the pseudarthrosis, which may also impinge on the cuff.

The diagnosis of os acromiale may be made on axillary projection radiographs, computed tomography (CT) or magnetic resonance imaging (MRI).

MRI may show marrow edema and degenerative changes at a pseudarthrosis.

SPLENIC ABSCESS

Axial T1 FS image showing large relatively thick walled fluid collection with debris and air pockets. Note the air fluid level anteriorly

Sagittal T2 Wt image showing the abscess with airfluid level anteriorly- suggests pyogenic abscess.



Axial DWI image showing mild restriction within the abscess.



·        The rarity of primary splenic abscesses is probably related to splenic phagocytic immune functions.

·        A splenic abscess may be bacterial, fungal, or granulomatous.

·        In infants and children, splenic abscesses occur most frequently in immunocompromised patients.

·        Abscesses may be single or multiple.

·        With fungal infections in an immunocompromised patient, abscesses are typically multiple.

·        Pyogenic abscesses can be secondary to underlying sepsis or spread by hematogenous seeding.

·        Amebic dysentery, otitis media, mastoiditis, peritonsillar abscess, cutaneous infection, pneumonia, empyema, appendicitis, osteomyelitis, and intravenous drug abuse are all risk factors.

·        Patients with hemoglobinopathies are also at risk for splenic abscess formation secondary to infarction and necrosis as well as functional asplenia.

·        Pyogenic abscesses manifest as ill-defined, hypoechoic lesions at US. Debris and internal septations may be present. In rare cases, gas bubbles may be seen.

·        If present, intralesional gas is pathognomonic for pyogenic infection.

·        At CT, pyogenic abscesses typically manifest as single, irregularly marginated lesions with low attenuation. Rim enhancement can be seen on contrast enhanced scans.

·        Fungal abscesses are small lesions, typically only a few millimeters in diameter.

·        The most common infecting organisms are Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans.

·        M tuberculosis, M avium intracellulare, and P carinii infection can have similar appearances.

·        Fungal abscesses have a variable appearance at US.

·        Typically, they manifest as rounded, hypoechoic lesions with a central area of increased echogenicity, creating a “target” or “bull's-eye” appearance. These findings correspond to fibrotic tissue surrounding a central inflammatory core at histopathologic analysis.

·        The “wheel-in-a-wheel” appearance is seen when the central hyperechoic portion becomes necrotic and hypoechoic.

·        Hepatosplenomegaly is usually associated with fungal abscesses. CT typically demonstrates multiple small, low-attenuation lesions. The lesions may be missed unless intravenously administered contrast material is used.

·        Reference: A Pattern-oriented Approach to Splenic Imaging in Infants and Children, November 1999 RadioGraphics, 19, 1465-1485.