Enostosis - Bone island

Commonly known as bone island

Mature cortical bone within the medulla
Due to failure of resorption during endochondral ossification
Asymptomatic

Features:
CT/Radiograph: 
- Spiculated margin - blends with the surrounding trabecular bone
- Dense sclerotic focus
MR:
- All sequences: Very low SI
Scintigraphy
- Typically no activity. Some may have increased activity

DDx:
- Dense osteoid osteoma
- Osteoblastoma

PVNS

Pigmented villonodular synovitis
- Unknown aetiology
- Synovial proliferation disorder
- intracellular Haemosiderin deposition (thus "Pigmented")

Monoarticular
Age 30-40s

Benign proliferation of synovium in the joint or in bursa/tendon sheath +/- hemorrhagic effusion
If occurs in the tendon sheath => then it is known as Giant Cell Tumor of the tendon sheath

Clinical features:
- Insidious onset
- Monoarticular arthropathy
- Swelling
- Stiffness
- Pain

Pathology:
- Hyperplastic synovium
- Lipid-laden foam cells, histiocytes, giant cells, haemosiderin deposits

Distribution:
- Knee > Hip > Ankle > Shoulder

Radiograph:
- Dense effusion
- Dense soft tissue mass (due to haemosiderin)
- Bone erosion
- Large subchondral cysts
- Preserved joint space
- Typically normal in the early stage

MRI:
- Joint effusion
- Focal / diffuse synovial thickening: Low signal T1w and T2w, and blooming artifact on GRE (due to hemosiderin deposition)

DDx:
- (repeated) Haemarthrosis such as Haemophilics
- Septic arthritis
- Articular amyloid deposition (similar in MRI appearance)

Rx:
- Synovectomy (~50% with local recurrence)

Bosniak classification for Renal Cyst

Applicable to US, CT or MR imaging.

	Features	Management
Bosniak I	Anechoic cyst Thin walled No septa, calcification, solid components No contrast enhancement	No intervention required	Class 1 Renal cyst
Bosniak II	Hairline-thin septa Fine calcification / Short thick calcification No contrast enhancement	No intervention required	Class 2 Renal Cyst Class 2. Notice the faint thin septa? Also a smaller simple cyst in the lower pole.
Bosniak IIF	Multiple hairline-thin septae +/- minimal thickening Minimal wall thickening Thick / Nodular calcification No soft tissue component	Needs follow-up
Bosniak III	Thick wall / septa, irregular / smooth	Needs surgical intervention	Class 3. Notice the thicker septa and larger size of the cyst? Class 3 Renal Cyst
Bosniak IV	Bosniak III + soft tissue component which enhances.	Clearly malignant

Psoriatic arthritis

Psoriatic arthritis

Polyarticular arthritis
Skin disease: Psoriasis (Skin rash)
Chronic inflammatory
40yo, Caucasian
?Factors involved: Genetic, Immune system, Environmental
HLA-B27 +ve in 60%

Hand:
- Most commonly involved skeleton
- Interphalangeal joint (PIJ, DIJ)
- 'Fluffy periostitis'
- Bony proliferation*
- Joint erosion from articular margin* to centrally.
- Tapering of one end, saucerisation of the other end of the articular surface: Pencil-in-cup deformity
- Preserved bony mineralisation (no osteopenia), ivory phalanx
- Ankylosis
- Diffuse soft tissue swelling: Sausage digit

SIJs:
- Asymmetric sacroiliitis, sclerosis, large erosion
- Ankylosis is UNcommon

Vertebra:
- More commonly involved in MALE
- Asymmetric
- Atlanto-axial subluxation
- Squarring of vertebrae
- Enthesitis: comma-shaped ossification, paravertebral (parasyndesmophytes)
- Thoracolumbar region

Others:
- MTPJ
- TA insertion of the Calcaneum: Fluffy periostitis & Erosion

*HALLMARKS for Psoriatic arthritis

DDx:
- Ankylosing spondylitis (Ossification less bulky, symmetric sacroiliitis)
- Reactive arthritis (Genitourinary symptoms)
- Hyperparathyroidism (similarity: presence of large SIJ erosion)

Modic changes in MRI

Modic classification

Use for different endplate marrow degenerative changes (which is postulated to result from same pathological process, but at different stages) in lumbar spine MR imaging.

Modic degenerative changes often accompanies disk degenerative disease (DDD)

The Modic change can be of mix type 1 and 2, type 2 and 3.

Modic type	T1w	T2w	Pathology
1 (oedema)	Hypointense	Hyperintense Modic1. Note also disk dessication.	Oedema & Inflammation
2 (fat)	Hyperintense	Iso/Slight Hyperintense Modic2. Note also disk dessication.	Marrow ischaemia, thus red marrow converts to fatty yellow marrow
3 (sclerosis)	Hypointense	Hypointense Modic3. Note also disk dessication.	Subchondral sclerosis Radiograph of the same patient with Modic 3 degeneration. Note sclerosis (arrow).

Note:

Disciitis can mimic Modic 1 degenerative change, when the adjacent bone marrows from the inflamed/infected disk is inflamed

Look at 3 things:
(1) Whether the intervertebral disk shows corresponding degenerative change (disk dessication) or shows inflammed (disciitis)

(2) Whether the bone or adjacent structures points to infection eg bone erosion, abscess formation

(3) Last but not least, correlate clinically - Lab changes, Clinical history

	Endplates	Intervertebral disk	Others
Modic 1	Low T1w, High T2w	Iso/Low T2w Usually dessicated (modic change accompanies disk degenerative disease)	Clinically non-toxic
Diskiitis	Same as above, but with features of diskiitis ie bone erosion	High T2w Inflammed disk	Presence of inflammation / abscess in adjacent structures (eg paraspinal, epidural abscess) Clinical and laboratory findings of infection

Normal Variant: Cervical Rib

Note the corresponding transverse process points caudally => Cervical origin

Incidental finding of Cervical rib.
Can be unilateral or bilateral.
0.5 - 8% of population*
Usually asymptomatic, but occasionally may give rise to complications.
Think about the anatomical structures that goes through the thoracic outlet, and the attachment of the scalene muscle.

Complications:
- Usually in adulthood
- Thoracic outlet syndrome
- Subclavian artery aneurysm as a result of compression

DDx:
- Hypoplastic 1st rib (rudimentary 1st rib)
- Elongated transverse process of C7

Key to differentiate from the other DDx:
(1) Check transverse process. Cervical transverse process points down, 1st thoracic transverse process points up.
(2) Check presence of joint space between the rib and the transverse process. Absent joint space means it's a elongated transverse process.

Right cervical rib. Note the transverse process pointing down.

*Reference from: Guttentag AR, Salwen JK. Keep your eyes on the ribs: the spectrum of normal variants and diseases that involve the ribs. RadioGraphics 1999;19:1125-1142

Case: Aortic Dissection and its classification

 Classification for Aortic Dissection

DeBakey	Stanford
I	A (60%)	Involves both Ascending and Descending aorta	Intimal flap present in both ascending (small circle) and descending (large circle) aorta. Same patient on Coronal view. Note the peri-aorta haematoma (pink arrow)
II		Involves the Ascending aorta, up to the aortic arch	Intimal flap present only in the ascending aorta. Same patient in Coronal view. Intimal flap in Ascending aorta. Intimal flaps. Don't mistake the aortic valves for intimal flap.
III	B(40%)	Involves the Descending aorta only.	Involves the Descending aorta only. Note the beak sign (arrow), which signifies the false lumen. Same patient in Pre-contrast phase.

Note: DeBakey system is less commonly used now.

How I remember DeBakey system: 

Type I for ONE whole stretch (from ascending to descending), the rest of the types are A and B.

How I remember Stanford's classification:
Type A for Ascending, Type B for Below.

Landmark: 
- Left subclavian artery: Distal to this = Descending artery

Important remarks in a report: *remember to evaluate the whole aorta from top down*

• Stanford type A (surgical management) or B (non-surgical management)
• Rupture or not? Presence of haemothorax is a quick and easy sign
• Origin and extent of the dissection
• Presence of aneurysm / Diameter of the aorta
• Identify the false and true lumen (important in interventional management) - this can be identified by tracing the dissection to the end, delayed enhancement in the false lumen
• Identify the complications:
• Involvement of the important arteries: coronary arteries, common carotid arteries, iliac arteries
• Involvement of end organs eg kidneys, intestines, resulting in ischemia / infarction (this is an indication for surgical management)
• Cardiac tamponade as a result of bleed into the pericardium
• Heart failure
• Identify presence of haematoma in the mediastinum, pleura, pericardial or aorta

Associated conditions:

• Connective tissue disorder: Marfan syndrome, Ehlers-Danlos syndrome
• Turner syndrome
• Conditions where the aorta is subjected to high pressure:
• Hypertension
• Aortic coarctation
• Aortic stenosis, Bicuspid aortic valve
• Pregnancy
• Cystic medial necrosis

Differential diagnosis:
- Penetrating atherosclerotic ulcer
- Intramural haematoma (IMH) - also a form of aortic dissection, but without breaching the intima
- Pseudodissection as a result of motion artifact on CT scanning

In any case, remember to pick up the phone and call the surgeons! Happy reporting.