STRESS FRACTURE OF FIBULA

PDFS-SAG

T1 SAGITTAL

T1 AXIAL

PDFS-AXIAL

A 17 year old football player presented with pain in left distal leg and ankle.
MRI shows an incomplete fracture line involving the distal fibular shaft along the lateral aspect with sparing of medial part and is associated with marrow oedema. There is periosteal marrow oedema around it, more on the anterolateral aspect.

STRESS FRACTURES OF FIBULA:

• They are usually secondary to repetitive overuse or stress as in runners, hikers and players.
• May be seen along with stress fractures of tibia or medial tibial stress syndrome or on their own.
• They account for approximately 10% of stress fractures
• They usually involve the distal one-third of fibula
• Plain radiographs may be normal initially. 
• They are best picked on MRI. 
• Bone scintigraphy is also useful.
• On MRI, typical features are those of periosteal thickening and periostitis along with oedema around the fibular cortex.
• An incomplete fracture line may be seen within the cortex.

 REFERENCES:

• Berger F, Jonge M D, Smithius R et al: Stress fractures. Radiology Assistant:2007( e-reference)
• Stoller D W, Ferkel R D, Li A E et al: The Ankle and Foot. Magnetic Resonance Imaging in Orthopaedics and Sports Medicine:Third Edition.Lippincott Williams & Wilkins:1003, 2007.

LHERMIETTE DUCLOS DISEASE

T2-AXIAL IMAGE

T1-AXIAL IMAGE

FLAIR-AXIAL IMAGE

CONTRAST ENHANCED T1 AXIAL IMAGE

A 7 year old child presented with ataxia and dizziness. MRI of brain shows increased volume and abnormal signal in right cerebellar hemisphere with a characteristic "striated" appearance on T2. There is mass effect on the 4th ventricle. It shows mild patchy enhancement.

SALIENT RADIOLOGICAL FEATURES:

• It is also called dysplastic cerebellar gangliocytoma
• Well defined cerebellar lesion involving usually unilateral hemisphere. 
• It may be large and involve the entire hemisphere as in this patient.
• Widened cerebellar folia with a characeteristic "layered" or "striated"appearance on T2
• It is hypointense on T1 and may show striated appearance with alternating layers of isointense and hypointense signal
• Calcification may be seen rarely
• These may show bright signal on DWI due to T2" shine through"
• There is no diffusion disturbance on ADC map.
• Rarely, some lesions may enhance
• MRS may show elevated lactate. There is diminished NAA, choline and myoinositol

REFERENCES:


Jones BV: Dysplastic Cerebellar Gangliocytoma. Diagnostic Imaging Brain: First Edition. Amirsys: I-6-70, 2005.  

PEDUNCULATED SUBSEROSAL FIBROID

T2FS SAGITTAL IMAGE SHOWING MULTIPLE UTERINE FIBROIDS. ARROW SHOWS STALK OF PEDUNCULATED FIBROID

STIR CORONAL IMAGE

T1 CORONAL IMAGE

A middle aged female with menorrhagia showed multiple uterine fibroids on ultrasound. Ultrasound also showed a pelvic mass just above the uterus the origin of which could not be clearly ascertained. MRI was done which clearly showed its connection to the uterine wall by a narrow stalk thus confirming its origin.

SUBMUCOSAL UTERINE FIBROID

MRI of the pelvis in a 22 year young lady with infertility showed a large submucosal fibroid of uterus.

• Sagittal and coronal T2FS and STIR images show a large submucosal leiomyoma that arises from the posterior uterine wall and causes significant distortion of the endometrial cavity.
• These can be differentiated from polyps on the basis of signal characteristics and location. Leiomyomas are hypointense on T2. Also, the origin of the leiomyoma is from the uterine wall rather than endometrium.

MIRIZZI SYNDROME

T2 HASTE AXIAL IMAGE SHOWING IMPACETD CALCULUS IN CYSTIC DUCT

T2 HASTE CORONAL IMAGE SHOWING IMPACTED CYSTIC DUCT CALCULUS CAUSING BILIARY OBSTRUCTION. MULTIPLE CALCULI ARE SEEN IN THE GB.

T2 HASTE AXIAL IMAGE SHOWING DILATED BILIARY SYSTEM

T2 HASTE CORONAL IMAGE SHOWING BILIARY OBSTRUCTION

3D RECIST IMAGE SHOWING BILIARY OBSTRUCTION BY THE IMPACTED CALCULUS

 MIRIZZI SYNDROME:   

It is best seen on ultrasound or MRCP which show gall stone impacted in the cystic duct or GB neck causing narrowing of the common hepatic duct and dilated intrahepatic bile ducts.

REFERENCE: 

• Federle MP: Mirizzi Syndrome. Diagnostic Imaging Abdomen: Second Edition. Amirsys: III-2-48, 2010.

PARAMENISCAL CYST

PDFS SAGITTAL IMAGE SHOWING LATERAL MENISCAL TEAR

PDFS SAGITTAL IMAGE SHOWING PARAMENISCAL CYST

STIR CORONAL IMAGE SHOWING TEAR IN LATERAL MENISCUS AND PARAMENISCAL CYST

STIR CORONAL IMAGE SHOWING PARAMENISCAL CYST

AXIAL GRE IMAGE SHOWING PARAMENISCAL CYST.

MENISCAL AND PARAMENISCAL CYSTS:

HOW THEY ARE FORMED?

• They are usually formed as a sequel to trauma or degeneration which inititaes necrosis near the peripheral margin of the meniscus leading to mucoid degeneration and softening of the meniscal collagenous tissue with local accumulation of synovial fluid. 
• More often, this fluid extends to the meniscocapsular margin thorugh the meniscal tear displacing the capsule peripherally and thereby forms a paramenical cyst in the surrounding tissues.
•  Rarely, fluid accumulates locally within the meniscal tear and is contained within the meniscus.

IMAGING:

• On MR, intrameniscal cysts are seen as small fluid pockets within the meniscus. Adjacent horizontal cleavage tear may or may not be seen.
• Parameniscal cysts are seen as well defined ( often septated) fluid collections in continuity with horizontal cleavage tears or complex meniscal tears with horizontal component.
• They are usually hyperintense on all fluid sensitive sequences. However, cyst may show low signal sometimes on T2, either due to dessication or hemorrhage.
• If large, parameniscal cysts may cause bony erosion.

LOCATION:
-Medial> Lateral
-Most common site is along posteromedial aspect of medial meniscus
-Lateral meniscus cysts more commonly arise from its anterior and mid portions
-Although, medial meniscal cysts are more common, lateral meniscal cysts are picked up more often clinically.
-Lateral cysts are better defined and tend to remain close to the joint margin.
-Medial meniscal cysts are more tightly bound to the medial collateral ligament and hence, fluid accumulation is usually some distance away from the meniscal tear. However, a thin connecting stalk is usually seen between the cyst and meniscal tear.

DIFFERENTIAL DIAGNOSIS: It is very important to see the associated meniscal tear with connection to the cyst.

• Semimembranosus/ Pes anserine bursitis
• MCL bursitis

 REFERENCE:

•  McCarthy CL, McNathy: The MRI appearance of cystic lesions around the knee.Skeletal Radiol. 33:187-209, 2004.