Malignant lesions of the acromion process:
Chondrosarcoma
Chondrosarcomas are malignant tumours characterised by the formation of cartilage matrix and are the third most common primary malignant tumour of bone1.
In our review we identified chondrosarcoma to account for 21.9% of acromial lesions.
Chondrosarcoma of the acromion process can have a primary or secondary origin.
Numerous types of primary chondrosarcoma exist; intramedullary,
clear cell,
juxtacortical,
myxoid,
mesenchymal and extraskeletal.
Imaging findings directly reflect the pathological appearances as the different subtypes show distinctive features.
In the shoulder girdle chondrosarcoma commonly affect the flat bones.
Imaging findings of a conventional chondrosarcoma classicaly demonstrate an ill-defined lytic and sclerotic lesion with a expansile remodeling component.
Fig. 1: Left shoulder radiograph demonstrating a destructive lytic lesion with associated endosteal scalloping arising centrally in the acromion process. This was later histologically confirmed to be a primary chondrosarcoma.
References: Royal orthopaedic hospital, Birmingham, UK
The area of sclerosis is usually represented as a chondroid ring and arc calcification.
On plain radiographs the identification of the aggressive features endosteal scalloping with soft tissue extention will usually warrant in further CT and MRI imaging.
Calcification can be seen if there is a large myxoid component.
Fig. 6: Post contrast T1 FS coronal image of the chondrosarcoma demonstrating a peripheral and septal enhancement around a lobulated cartilage with few areas of confluence. Higher grade lesions demonstrate more generalised enhancement with surrounding low signal regions of necrosis.
References: Royal orthopaedic hospital, Birmingham, UK
Imaging of acromion process chondrosarcoma
( Fig. 1 - Plain radiograph )
( Fig. 2 Fig. 3 - CT)
( Fig. 4 Fig. 5 Fig. 6 - T1W,
T2W & T1W FS post contrast imaging)
Treatment via surgical resection with wide margins is usually always performed.
Radiotherapy and chemotherapy is not very effective and can be used for palliation or for surgically in-accessible lesions.
Adequate safety margins are needed and should be planned carefully in conjunction with imaging.
Metastasis:
The acromion process is a rare and atypical location for metastasis to occur with very few cases reported in the current literature.
In our review of referred cases 21.9% of the suspected acromial lesions were diagnosed as metastasis .Metastasis must be considered in the differential diagnosis of any acromial lesion in patients >40 years of age.
Metastasis occured from primary breast and renal cell carcinomas.
Other sites where metastasis can occur include,
lung,
colon and thyroid.
Breast cancer spread to bone is still not clearly understood,
however radiographic findings of breast metastasis to bone usually is related to the mixed osteoblastic and osteolytic appearances.
Imaging presentations can vary and can present on radiographs as ill-defined or well defined osteo-lytic lesions.
Fig. 13: Axial CT of same patient in Fig. 12 demonstrating an expansile poorly demarcated lytic lesion in the acromial process in a patient with renal cell carcinoma. Tissue diagnosis confirmed metastasis.
References: Royal orthopaedic hospital, Birmingham, UK
Sclerotic components may also be seen on plain radiographs of the shoulder.
Imaging of acromion process metastasis
Breast Metastasis
(Fig. 7 - Shoulder radiograph)
(Fig. 8 - Volume rendered CT)
(Fig. 9,
Fig. 10 Fig. 11 T1W,
STIR & T2W MRI)
Renal cell carcinoma metastasis
(Fig. 12 Fig. 13 RCC xray and axial CT)
Accepted treatment methods include curettage or surgical resection with filling of the bony defect with a bone graft.
Marginal resection is necessary for more aggressive metastasis.
Multiple myeloma - Plasmacytoma:
Multiple myeloma is a nneoplastic plasma cell disease producing abnormal quantities of immuoglubins resulting in tumour formation,
osteolytic bone disease,
renal dysfunction and hematopoiesis2.
An occurrence of an acomial myeloma lesion is rare.
Our review confirmed 6 cases of acromial lesions diagnosed as a myeloma.
A solitary presentation is referred to as a plasmacytoma. Solitary plasmacytomas presenting as acromial lesions were also noted in our review.
Multiple myeloma must be included in the differential diagnosis of a lytic acromial bone lesion. Common imaging findings demonstrate a lytic punched out lesion which can be ill defined or well defined.
Fig. 19: Sagittal MRI post Gadolinium demonstrating contrast enhancement in the acromion lesion in a multiple myeloma patient. Findings are keeping with a myeloma deposit.
References: Royal orthopaedic hospital, Birmingham, UK
Multiple myeloma acromion lesion Imaging
(Fig. 14 Fig. 15 - Shoulder radiograph and CT)
(Fig. 16 Fig. 17 Fig. 18 Fig. 19 - T1W,
T2W,
T1 FS,
Post contrast T1 FS)
Plasmacytoma acromion lesion Imaging
Fig. 21: Axial CT slice demonstrating an expansile soft tissue mass with evidence of a thin cortex in the acromion. There is no evidence of an identifiable intra-lesional matrix. Note the wires on the surface of the shoulder in preparation for a CT guided biopsy. This was later confirmed to be a plasmacytoma.
References: Royal orthopaedic hospital, Birmingham, UK
(Fig. 20, Fig. 21, Fig. 22 - Shoulder radiograph,
CT and STIR sequence MRI demonstrating a solitary plasmacytoma of the acromion)
In myeloma/plasmacytoma the treatment options are usually sufficient with chemo and radio therapy along with conservative surgical measures.
This is the best reported method to preserve shoulder function.
Ideally a solitary plasmacytoma should be distinguished from multiple myeloma as the treatment and prognosis differs given the systemic involvement in multiple myeloma.
Systemic involvement will usually warrant chemotherapy with autologous stem cell transplant.
Lymphoma
Primary non-Hodgkins lymphoma remains extremely rare representing <5% of malignant bone tumours3.
Our review represented 9.4% of all acromial lesions referred.
The peak incidence of primary lymphoma is described to be in the 6th and 7th decade of life. Involvement of the scapula is extremely rare.
General imaging findings of lymphoma involvement in the acromion include permeative osseous destruction with an intact cortex with an associated infiltrating soft tissue mass.
Xray findings: There is oftent extensive involvement of the bone with significant permeative bony destruction.
The soft tissue extention/mass is usually disproportionately large.
Lamellated periosteal reaction
Once the diagnosis is confirmed from biopsy or fine needle aspiration,
treatment should commence with chemotherapy and immunotherapy agents to reduce the size of the lesion.
Benign lesions of the acromion process
Osteochondroma:
These are benign bone forming tumours that usually present in the shoulder,
are usually aysymptomatic but can present with night time pain in young adults and are often relieved by anti-inflammatories.
Osteochondromas are most common primary neoplasm in the scapula however the occurrence in the acromion process is extremely rare with very few cases described in the literature4.
It is very common for the nocturnal pain in the shoulder to be associated with rotator cuff impingement syndrome,
however the diagnosis of an osteoid osteoma should be considered in younger patients presenting with these symptoms.
Fig. 23: T1W coronal slice of the left shoulder demonstrating a low signal intensity lesion in the acromion process. Further MRI sequences confirmed a benign juxtacortical chondroma.
References: Royal orthopaedic hospital, Birmingham, UK
Imaging of acromion process osteochondroma
(Fig. 23, Fig. 24, Fig. 25 - T1W,
T2W and post contrast MRI slices demonstrating findings in a patient with a juxta cortical acromion process chondroma.)
Treatment options include supportive medication,
surgical resection and more novel therapies such as percutaneous radiofrequency ablation.
Osteochondromas usually require no treatment unless there is a risk of fracture or soft tissue compression.
If patient symptoms are adequately controlled with anti-inflammatories then surgery should only be advised once patients become symptomatic.
There have been cases of spontaneous healing of the lesion within 3-4 yrs controlled only on anti-inflammatory medication5.
Osteoid osteoma:
This is a non-malignant bone lesion constituting 10% of benign bone forming lesions in the scapula6.
We found 1 diagnosed case of osteoid osteoma referred in as an acromial lesion.
Development of these lesions in acromion are extremely rare.
The lesion usually forms in the 2nd and 3rd decade of life and its characteristic feature is nocturnal pain alleviated by NSAID’s. On plain radiographs periosteal changes which are characteristic for malignant tumours can be demonstrated.
Therefore osteoid osteoma has to be differentiated from malignant forming bone tumours and infection.
Imaging findings of an osteoblastoma of the acromion process
Fig. 26: T1W coronal MRI of the right shoulder demonstrating a low to intermediate signal intensity, homogenous lesion in the acromion process which was later confirmed to be a benign osteoblastoma.
References: Royal orthopaedic hospital, Birmingham, UK
Surgical resection of the tumour is recommended if the patient is symptomatic.
A radical resection of the lesion is confirmed by the alleviation of pain.
Post surgical CT will confirm the area of resection and can also assess for trauma caused by the surgery,
as even a minimally invasive technique can cause the development of osteoarthritis.