What rare anomaly can be seen in this 28-year-old’s foot?  It’s often difficult to recognize something that’s not there!

This 28-year-old female presents with ankle and foot pain, with no recent injury and no history of surgery. Have a look at images 1 through 5, and see if you can come up with the rare diagnosis in this case.

Sagittal T1W aTSE

Sagittal T1W aTSE

Coronal PDW SPAIR

Coronal PDW SPAIR

Coronal PDW SPAIR

 

On the images provided, note apparent absence of the tarsal navicular bone, except for a small accessory ossicle dorsally (image 6, arrow). The talar neck appears elongated and the talar head enlarged in size (better seen on images 7 and 9).

Sagittal T1W aTSE

Sagittal T1W aTSE

Coronal PDW SPAIR

Coronal PDW SPAIR

Coronal PDW SPAIR

 

The rare diagnosis is congenital solid osseous talonavicular coalition. Note that the enlarged talar head directly articulates with the cuneiform bones. On images 7 and 10, the arrow indicates fusion of the middle cuneiform bone and base of the second metatarsal, as an additional anomaly. Note also multifocal, prominent bone marrow edema, seen as gray T1 marrow signal in the talus and calcaneus adjacent to the posterior subtalar joint on image 6 (arrows), and bright marrow signal on the PD fat sat coronal images 8 and 9 (arrows), consistent with osseous stress reaction involving body of talus and calcaneus and the lateral cuneiform and cuboid bones.

One of the rarest of tarsal coalitions, talonavicular coalition was first described by Anderson in 1879. Tarsal coalition represents a failure of embryologic mesenchymal segmentation, with calcaneonavicular and talocalcaneal coalition being more common types of tarsal coalition. The incidence of tarsal coalition in the general population has been thought to be at around 1 to 2%, but the incidence of the rare talonavicular coalition seen in this case is unknown.

Talonavicular coalition has shown a strong familial or genetic predisposition, and appears to be inherited in an autosomal dominant pattern with high penetrance and variable expression.  Like other coalitions, this anomaly is frequently bilateral, and is associated with other skeletal anomalies including symphalangism, clinodactyly, clubfoot and peroneal spastic flatfoot.  On exam, these patients typically demonstrate pes planus.  Often, these patients are relatively asymptomatic, compared to patients with the more common calcaneonavicular or talocalcaneal coalitions which affect hindfoot mobility.  When symptomatic, conservative treatment with orthotics and footwear modification is most common, although surgical treatment may be indicated for chronic painful flatfoot if conservative treatment fails.

Check out MRI Online for more case review.

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Dr. Stephen Pomeranz

Dr. Richard J. Rolfes

 

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What sign is a can’t-miss in this case?

Case: A 64-year-old male presents with a three-year history of progressive back pain, lower limb weakness and unstable gait. He experiences no bowel or bladder difficulty and there is no history of prior trauma or spinal surgery. Physical examination revealed lower limb weakness with spasticity.

Sagittal T1

Sagittal T2

Axial T2

Sagittal T1 post contrast

Sagittal CT myelogram

Axial CT myelogram

Axial CT myelogram

 

Findings: A focal dorsal indentation of the thoracic spinal cord is present at the T6 level, with associated compression and deformity of the cord which is displaced anteriorly (Images A-C).

Extensive abnormal cord signal abnormality is present below the level of the indentation extending to the T8 level (Image B).

No abnormal enhancement is present on the post contrast image (Image D).

The CT myelogram shows the “upside down scalpel sign” with the characteristic focal indentation of the dorsal thoracic spinal cord with widening of the dorsal cerebrospinal fluid space, and cord expansion below the level of the dorsal indentation (Image E, pink arrow).

Corresponding axial CT myelogram image at the level of the dorsal indentation (Image F, green arrow) demonstrates a remaining thin CSF space between the anterior cord and the ventral theca. This subtle but key finding helps exclude a diagnosis which is almost identical visual on MRI, namely spinal cord hernia through an anterior rent in the dura. Image G is an axial image below the level of the indentation.

Diagnosis: Dorsal thoracic arachnoid web with spinal cord compression.

Differential: Ventral cord herniation; Dorsal arachnoid cyst (simulates thoracic cord hernia).

Discussion: Spinal arachnoid webs represent intradural extramedullary bands of arachnoid tissue that extend to the pial surface of the spinal cord. They typically occur in the thoracic spine producing a focal indentation on the dorsal spinal cord.

The characteristic dorsal indentation of the cord has been described as the “scalpel sign,” due to the resemblance on sagittal imaging to a scalpel, with the blade pointing posteriorly.

The differential in this case is that of ventral spinal cord herniation, or a dorsal arachnoid cyst. In ventral spinal cord herniation, there is deformity on the ventral surface of the cord as it protrudes through a ventral dural defect, and there is NO space between the cord and the ventral theca. Arachnoid cysts can be identified on imaging by their marginated thin but low signal walls, and they produce a relatively smooth scalloping on the cord surface. On CT myelography an intraspinal filling defect or delayed filling of the arachnoid cyst is sometimes present.

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Editor’s note: This case was submitted by Dr. Tiffany So, who was selected for a scholarship for our upcoming Melbourne Case Review course. Congratulations to Dr. So!

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Can you classify this shoulder injury?

This 17-year-old presents with acromioclavicular (AC) separation. How do we classify shoulder injuries in young adults at ProScan?

Coronal PD FSE Fat Sat

 

Image 1 (green line) indicates a measured distance 11mm between the acromion and clavicle (normal in males is 7mm; females is 6mm). Note edema surrounds the clavicle. No microtrabecular fracture.

Sagittal T2 FSE Fat Sat

Coronal PD FSE Fat Sat

Coronal PD FSE Fat Sat

Sagittal T2 FSE Fat Sat

Coronal PD FSE Fat Sat

Coronal PD FSE Fat Sat

 

Injury is classified according to the system of Tossy, which simplifies the six shoulder descriptors by Rockwood and Green, and is helpful in MRI characterization. Tossy 1 represents contusion or strain, without offset of the inferior margin of the acromion at the clavicle. Tossy 2 has less than 50% offset or overlap with subtype 2A involving sprain of the trapezoid segment and 2B involved both conoid and trapezoid segments of the CC ligament. Tossy 3 has greater than 50% overlap. In this case, we see that the more lateral ligament (trapezoid) from the clavicle to the coronoid process demonstrates a high-grade tear (image 2, orange arrow). Further, there is a more swollen and perhaps minimally torn more medial conoid ligament (image 3, red arrow, and image 4, yellow arrows).

The cuff and labrum are normal, and no fracture is seen. Mixed hemorrhage and edema along the superior joint space margin with low-grade strain of a few deltoid fibers originate at the metaphysis and epiphysis of the distal clavicle separate from the AC joint (image 5, pink arrows).

Image 6 (purple arrow) highlights nominal strain, and contusion of the posterior most fibers of the lateral trapezius.

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Dr. Stephen Pomeranz

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Is there a bird in my head?

This 16-year-old male presents with a head injury. Denies neck pain, chest pain, abdominal pain or extremity pain. States that he did lose consciousness. Focus on the elongated right styloid process in image 1, and the elongated left styloid process of image 2. What do you think the diagnosis could be?

CT – MPR auxiliary image

CT – MPR auxiliary image

 

If you came up with Eagle syndrome (the bird in my head) as the diagnosis, then you hit the nail on the head. Image 3 highlights the elongated right styloid process measured at 4.6cm. Image 4 shows the elongated left styloid process measuring 3.4cm.

CT – MPR auxiliary image

CT – MPR auxiliary image

 

Clinical presentation of Eagle syndrome can be divided into two main subtypes:

1 – Due to compression of cranial nerves
2 – Due to compression of the carotid arteries

Cranial nerve impingement symptoms typically include facial pain when turning the head, dysphagia, foreign body sensation, pain on extending the tongue, change in voice, sensation of hypersalivization, and/or tinnitus/otalgia. On palpation of the styloid process tips, symptoms should ideally be exaggerated.

Arterial impingement symptoms include mechanical compression which would result in visual symptoms, syncope, carotid dissection, or sympathetic plexus irritation (carotodynia) such as eye pain or parietal pain.

Radiographic features of Eagle syndrome include styloid processes longer than 3cm which can be either unilateral or bilateral. Sometimes, styloid processes are elongated or the stylohyoid ligament is calcified.

Typical treatment includes transpharyngeal injection of steroids/local anesthetic agents. Severe cases would involve surgical excision either via transoral approach or a lateral approach. Transoral approach has the disadvantage of increased infection rates, but does not cause external scarring.

 

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Dr. Stephen Pomeranz

Dr. Benjamin J. LeSar

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What is the cartilage telling us?

This 61-year old woman presents with weakness, limited range of motion, and pain of the left shoulder. No history of recent injury is present.

Q1 – With regard to the bone lesion, which of the following findings is present in the MRI study?

(a) Perilesional osseous edema
(b) Rim of sclerosis
(c) Cartilaginous matrix
(d) Pathologic fracture
(e) Endiosteal scalloping

Q2 – Which is the most likely diagnosis of the bone lesion based on the MRI findings?

(a) Giant Cell Tumor (GCT)
(b) Bone infarct
(c) Chondromyxoid fibroma
(d) Breast cancer metastasis
(e) Enchondroma

Q3 – Which of the following statements is false regarding chondral lesions?

(a) Clear cell chondrosarcoma typically involves the end of bone
(b) Cortical scalloping is a supportive finding for chondrosarcoma over enchondroma in the long bones
(c) Chondroblastoma is typically located in the epiphysis of the tubular bones
(d) Enchondroma is usually diaphyseal in location when it involves the short tubular bones
(e) Enchondromas of long tubular bones carry a higher risk of malignant transformation than short tubular bones

Q4 – Which of the following statements is true regarding chondrosarcomas?

(a) The pelvis is an unlikely site for chondrosarcoma
(b) Osteochondromas can transform into chondrosarcoma
(c) Chondrosarcoma is the most common primary malignant bone tumor
(d) Ollier’s disease presents with multiple enchondromas and hemangiomas
(e) Brain is the most common site for chondrosarcoma metastasis

 

Sagittal T2 FSE Fat Sat

Coronal PD FSE Fat Sat

Axial T2* ADAGE

Coronal T1 FSE

Sagittal T2 FSE Fat Sat

Coronal PD FSE Fat Sat

Axial T2* ADAGE

Coronal T1 FSE

 

A1 – (c) Cartilaginous matrix. The lesion demonstrates the signal intensity characteristics of the cartilaginous matrix.

(a) is false. Proton density (PD) clearly demonstrates the red marrow low signal (image 4, pink arrow), which disappears on T2. Bone marrow intensity should not be confused with osseous edema. (b), (d) and (e) are also false. Lobulated contours of the lesion are free of a “low signal” sclerotic rim. The lesion mainly demonstrates central position, and there is no cortical scalloping even at the regions where it is intimately close to cortex.

A2 – (e) Enchondroma. An enchondroma has been shown on MRI study.

(a) is false. Giant Cell Tumor (GCT) is a benign, but locally aggressive, osteolytic skeletal neoplasm. They are seen in younger patients (between the ages of 20 and 40; average age is 32). In more than 85% of the cases, GCT abuts articular surface or comes within 1 cm of the articular surface of the long tubular bones. Shoulder region is not a common location for GCTs. They tend to be eccentric and the overlying cortex is thinned, expanded or deficient. The septa are also delicate. GCTs demonstrate T1 low to intermediate solid component with low signal periphery, low signal intensity (variable) on T2, and no cartilage matrix calcification / mineralization. In other words, no high T2 signal “popcorn” appearance or “arcs and whorls type calcification”.

(b) is false. Bone infarcts demonstrate serpiginous peripheral low signal due to granulation tissue and to lesser extent sclerosis on T1. On T2-weighted images hyperintense inner ring of granulation tissue and a hypointense outer ring of sclerosis produces “double line sign.” The central signal is usually isointense to bone marrow (hyperintense T1). Bone infarcts do not demonstrate cartilaginous matrix or arcs and whorls type calcification. T1 hyperintensity is not a characteristic of chondroid lesions. Marked T2 hyperintensity (cartilage matrix) is not a feature of standard infarcts.

(c) is false. Differential diagnosis of enchondroma from chondromyxoid fibroma (CMF) is often difficult. Histologically, CMF consists of myxoid, chondroid, and fibrous elements, and appears very similar to chondrosarcoma. CMF has the same appearance on MRI as other cartilage tumors, which is hypointense on T1 and hyperintense on T2-weighted images. They are often seen as lobulated masses. Diagnostic aids in our case are the patient’s age and the rarity of chondromyxoid fibroma. Our patient is not in the right age group for CMF as patients are usually younger. The majority of CMFs occur in the second and third decades. CMF are extremely rare, accounting for less than 1% of all bone tumors.

(d) is false. There is no history of breast cancer. Breast cancer metastases can be sclerotic or lytic, but do not demonstrate cartilaginous matrix.

A3 – (a) Clear cell chondrosarcoma typically involves the bone end. Flat bone involvement by clear cell chondrosarcoma is unusual. A typical feature of clear cell chondrosarcoma is its predilection for the epiphysis of the long tubular bones unlike predilection to metaphyseal location of conventional intramedullary chondrosarcoma. Clear cell chondrosarcoma involves the proximal end of long tubular bones in 90% of the cases. The differential diagnosis includes chondroblastoma in younger patients due to their location.

(b) is true. Cortical scalloping is a finding supportive of chondrosarcoma over enchondroma in the long bones. Additionally, the depth of endosteal scalloping is considered a valuable distinguishing feature between a long bone enchondroma and chondrosarcoma. Deep (greater than 2/3 of the normal cortical thickness) scalloping is seen in about 90% of chondrosarcomas. This feature may be seen in only 10% of enchondromas.

(c) is true. Chondroblastoma is a benign cartilaginous tumor that occurs in the epiphysis of skeletally immature individuals, between 10-25 years of age. It is more common in patients with open growth plates.

(d) is true. Enchondromas are usually diaphyseal in location when they involve the short tubular bones of the hands and feet (40-65%).

(e) is true. Enchondromas of long tubular bones carry a higher risk of malignant transformation than short tubular bones, although this rule does not apply to Ollier’s or Mafucci’s Diseases or Syndromes.

A4 – (b) Osteochondromas can transform into chondrosarcoma. Both enchondromas and osteochondromas can undergo malignant degeneration to chondrosarcoma.

(a) is false. Although the most common location for conventional intramedullary chondrosarcoma is the long tubular bones (femur followed by proximal humerus), pelvic bones are involved in 25% of the cases. Other bones that can be involved are scapula, ribs and sternum. Spine, craniofacial bones, and sesamoids are less frequent sites for chondrosarcoma.

(c) is false. The most common primary bone malignancy is multiple myeloma, followed by osteosarcoma. Chondrosarcoma follows these two.

(d) is false. Ollier’s disease is known as enchondromatosis, and is not associated with hemangiomas. Mafucci’s syndrome is characterized by multiple enchondromas and hemangiomas, particularly within the hands and feet. Both are associated with increased risk of malignant transformation of enchondromas into chondrosarcoma (5%-30% in Ollier’s disease, and 20% in Maffucci’s).

(e) is false. The brain is NOT a common site for chondrosarcoma metastasis. Most common metastasis sites of chondrosarcoma are lungs, regional lymph nodes and liver.

POMERANZ PEARL #1: You should never confuse with chondromyxoid fibroma, which look more like nonossifying fibroma, are rare and do NOT calcify.

POMERANZ PEARL #2: True chondroid matrix is present in…

Enchondroma: 100%
Chondroblastoma: 50%
Chondromyxoid fibroma: 0%

POMERANZ PEARL #3: Enchondromas MUST have calcification unless or except in phalanges; they NEVER have periostitis; pathologists struggle to differentiate benign from malignant; pain is the BEST way to predict malignant degeneration; they are typically NOT at the bone end unless in phalanges.

 

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References:

Chakarun CJ, Forrester DM, Gottsegen CJ, et al. Giant cell tumor of bone: review, mimics, and new developments in treatment. Radiographics. 2013 Jan-Feb;33(1):197-211.

Nichols RE, Dixon LB. Radiographic analysis of solitary bone lesions. Radiol Clin North Am. 2011 Nov;49(6):1095-114.

Rajiah P, Ilaslan H, Sundaram M. Imaging of primary malignant bone tumors (nonhematological). Radiol Clin North Am. 2011 Nov;49(6):1135-61.

 

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What has happened to this man’s spine?

This 44-year-old male presents with back and right leg pain. Take a look at the first two images without arrows before looking at the duplicate images with arrows.

Q1 – The most likely diagnosis is:

(a) Schwannoma
(b) Meningioma
(c) Epidural lipomatosis
(d) Synovial cyst

T2/S/TSE 16/PSAT

T2/T/TSE 16/MMT

T2/S/TSE 16/PSAT

T2/T/TSE 16/MMT

 

A1 – (d) Synovial cyst

 

Synovial cysts are associated with arthropathic facet joints, and rise near the joint articulation.

They are most common in the lumbar region, but can occur in the cervical region occasionally and thoracic rarely. L4-5 and L3-4 are the most common sites.

Neurally-based root sheath cysts show an intimate relation to the adjacent nerve root.

Percutaneous drainage has a high recurrence rate. Surgical resection is usually required, but due to adherence of the synovial tissue to the dura, it may be complicated by cerebrospinal fluid leak.

Synovial cysts often contribute to compressive radiculopathy. Sometimes they may prolapse posteriorly out of the spinal canal.

Gas within the cyst is pathognomic for synovial cyst and may be seen in the absence of infection. Cysts may be hemorrhagic, and contain debris contributing to a complex imaging appearance with variable T1 signal.

Synovial cysts are often proteinaceous or hemorrhagic, and therefore not always darker than muscle on T2.

 

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Reference:

1. Bjorkkengren AG. Symptomatic Intraspinal Synovial Cysts. AJR 1987; 149(1):105-107.

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This mass was a handful

This 61-year-old right-hand dominant female presents with a left hand mass. Mass (green arrows) has been present for approximately 15 years, and has been slowly enlarging. Patient states she had left side carpal tunnel release, and noted the mass a few months later. The mass is somewhat tender, and she denies numbness or tingling.

Q1 – Which is the most likely diagnosis?
(a) Tumoral calcinosis
(b) Synovial sarcoma
(c) Myositis ossificans / heterotopic bone formation
(d) Synovial chondromatosis
(e) Pigmented Villonodular Synovitis (PVNS)

Lateral Radiograph

Coronal T2 Fat Sat

 

A1 – (a) Tumoral calcinosis

 

Q2 – Regarding tumoral calcinosis, which of the following is not true?
(a) More frequent in Blacks
(b) One third familial tendency
(c) Near joints
(d) May effect skin, marrow, and teeth (dental pulp Ca+ and root enlargement)
(e) No known predisposing factors

Q3 – Regarding tumoral calcinosis, which of the following statements is false?
(a) Predisposing factors are metabolic and related to calcium, phosphorus, and vitamin D
(b) Encapsulated rather than spreading
(c) Fibrous septa
(d) Inflammatory component common
(e) “Zonule effect”

Q4 – Regarding tumoral calcinosis, which is not true regarding imaging?
(a) Prefers extensor surface
(b) Radiolucent septa “chicken wire” appearance
(c) Commonly involves intra-articular space
(d) MR/CT calcium-fluid level “sedimentation sign”
(e) High signal around low signal on T2 MR

Q5 – Regarding tumoral calcinosis, which is not true regarding imaging?
(a) Average number of lesions per patient is ~ 3
(b) Bone scan is negative
(c) “Sedimentation sign” on MR/CT = more active disease
(d) Pseudoxanthoma elasticum-like syndrome of skin, vessels and retina
(e) Associated CPPD arthrosis or calcific myelitis

 

A2 – (e) No known predisposing factors
A3 – (e) “Zonule effect”
A4 – (c) Commonly involves intra-articular space
A5 – (b) Bone scan is negative

 

Differential Diagnosis of Soft Tissue Masses in or about the Joints:

1. TUMOR-LIKE: Tumoral calcinosis, pigmented villonodular synovitis, ganglion pseudocyst, synovial cyst, myositis ossificans, heterotopic bone

2. BENIGN: Synovial lipoma, myxoma, synovial chondromatosis/chondroma, nodular fasciitis

3. MALIGNANT: Synovial sarcoma, clear cell sarcoma

Tumoral Calcinosis Clinical Features:

1. Usually children and young adults

2. Increased incidence in black / African-Americans

3. Familial tendency in 33% of the cases

4. When familial, autosomal dominant with variable expression

5. Calcified bulky periarticular mass around the hip, elbow, shoulder, foot or wrist

6. Can be associated with CPPD and pseudoxanthoma elasticum syndrome

7. Skin ulceration, marrow and dental changes

8. The etiology is most likely metabolic with an elevated calcium phosphorus product and sometimes increased vitamin D. Trauma and idiopathic causes have been reported. Some association with renal dysfunction in secondary form.

Tumoral Calcinosis Radiography:

1. Extensor surface calcified periarticular mass

2. Radiolucent septations or “chicken wire sign” as opposed to the “zonule sign” of myositis ossificans. Zonule sign = calcification / ossification from the outside to inside

3. Range of motion preserved unlike myositis ossificans

4. Extraarticular bursa created around the lesion

5. More often multifocal than myositis ossificans average three lesions per individual

6. Calcium fluid levels on CT and MR so-called “liquid calcium or sedimentation sign” unlike myositis ossificans; sedimentation sign equals more active disease

7. Hot on bone scan

MRI:

1. Usually low central signal on T1

2. Usually high signal on T2 peripherally, the opposite of myositis ossificans due to adventitial bursae. In myositis ossificans, the high signal is usually in the periphery eg “zonule phenomenon.”

3. High signal interstitial septations water-like in character

4. Pseudoxanthoma elasticum associated with skin and vascular calcification with retinal angioid streaks

5. Associated CPPD arthropathy

6. Dental abnormalities may include root enlargement and intrapulp calcification, marrow involvement as areas of calcification

Differential Diagnosis of Periarticular Calcification Includes:

1. Scleroderma

2. Other collagen vascular diseases, especially dermato-/polymyositis

3. Chronic renal failure so-called secondary tumoral calcinosis with elevated Ca+, calcium-phosphorus product

4. Milk-alkali syndrome

5. Synovial sarcoma- usually periarticular. Bulky, aggressive, heterogeneous mixed T2 intermediate signal.

6. Trauma or traumatic exostosis (including turret exostosis)

Tumoral Calcinosis Treatment:

1. Phosphate depletion therapy using:

(a) Aluminum hydroxide
(b) Acetazolamide

2. Surgical excision

 

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What is this 34-year-old’s controversial brain diagnosis?

This 34-year-old male presents with occipital headaches.

Q1 – Looking at image 1, what do you think the most likely diagnosis would be?

Sagittal T1

 

A1 – This patient has Chiari I malformation.

Sagittal T1

 

Q2 – Which of the following is true? Chiari I malformation features:

(a) Male predominance
(b) Symptoms likely markedly increased with greater than 5 millimeters of ectopia
(c) Main indication for posterior fossa decompression is headache persisting greater than 1 year
(d) Variance of tonsilar position with patient age

Q3 – Associated skeletal abnormalities with Chiari I include all of the following except:

(a) Klippel-Feil
(b) Atlanto-occipital assimilation
(c) “Spit cord” syndrome
(d) Platybasia
(e) Retroflexed dens

The diagnosis of Chiari I is controversial. Isolated tonsillar ectopia, while considered abnormal when greater than 4 millimeters, does not necessarily implicate Arnold-Chiari malformation as a diagnosis or the cause of symptoms. Other signs to support the diagnosis must include pegged-shaped tonsils, small occiput, proper symptoms (e.g. nystagmus, headaches, etc.), and especially syringohydromyella with or without the skeletal findings of Chiari I. These skeletal findings most prominently include:

Atlantooccipial assimilation
Klippel-Feil syndrome
Platybasia
Retroflexed dens

It is critical to be sure low-lying tonsils are not due to sagging from intrathecal hypotension or downward pressure from intracranial hypertension. Decompression or lumbar puncture in such circumstance may be contraindicated.

Up to 30 percent of patients with tonsillar ectopia between 5 and 10 millimeters may not be symptomatic. If the patient is not symptomatic, they do not require treatment. Syrinx is the only widely accepted definitive indication for surgical treatment. Non-stereotypic headaches are not a surgical indication by themselves.

Patients with Chiari II are characterized by lumbar dysraphism, specifically myelomeningocele or lipomyelomeningocele. Medullary kinking or Z-deformity at the craniocervical junction with descent not only at the tonsils but also the medulla is seen in Chiari II.

A2 – (d) Variance of tonsilar position with patient age

A3 – (c) “Spit cord” syndrome

 

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Reference:

1. Elster et. al. Radiology 1992; 183 (2).

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What is the uncommon diagnosis in this case? It’s a difficult one!

Case: A 42-year-old male presents with a nine-month history of burning pain and numbness in his right calf which extends to the lateral aspects of the plantar surface of his foot. He has a full range of movement and normal power within his right leg and foot. There is no muscle atrophy and reflexes are normal. He has no history of trauma. What is the diagnosis?

Axial PD Fat Suppression

Axial PD Fat Suppression

Axial PD Fat Suppression

Axial PD Fat Suppression

Axial PD Fat Suppression

Coronal T2 Fat Suppression

Coronal T2 Fat Suppression

Coronal T2 Fat Suppression

 

Findings: The images demonstrate a multilobulated ganglion arising from the proximal tibiofibular joint (images D, F-G, red arrows); which extends along the articular branches of the tibial nerve to the popliteal fossa (images D-E, H, blue arrows). Extrusion of the cyst within the tibial nerve sheath from the level of the knee joint proximally over a length of four centimeters (images B-C, H, green arrows); with displacement of nerve fibers, representing the signet ring sign (image C). Perineural edema extends proximally within the tibial nerve to the sciatic bifurcation (image A).

Diagnosis: Intraneural ganglion of the tibial nerve.

Differential: Cystic peripheral nerve sheath tumor, cystic nerve degeneration from prior trauma, extraneural ganglion, adventitial cyst of popliteal artery, unusual dissecting “Baker’s cyst.”

Discussion: Intraneural ganglion cysts involving the peripheral nerves are an uncommon but recognized cause of neuropathy that can present with pain, paresthesia or muscle weakness. At the knee, the peroneal nerve is the most commonly involved, with tibial nerve involvement being extremely uncommon. The peroneal nerve may undergo primary intrinsic internal cystic degeneration after trauma especially after being impacted by a car bumper. Cystic degeneration may occur within a matter of weeks.

This case demonstrates the previously-described MRI “signet ring sign,” associated with intraneural ganglia, which represents the intraneural cyst positioned eccentrically within the epineurium of the nerve, with displacement of nerve fascicles. The communication with the proximal tibiofibular joint is well appreciated on MRI, representing the “tail sign” (red and pink arrows).

A ganglion is actually a “pseudocyst” and not a true epithelial-lined cyst. It arises from degeneration of tendon sheath or capsule with a slow leak or ooze that is marginated by fibrous tissue.

Treatment of symptomatic intraneural ganglion involves percutaneous decompression or surgical excision to reduce nerve compression and secondary muscle denervation.

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Editor’s Note: This case was submitted by Dr. Tiffany So, one of our scholarship winners for our December 2017 Melbourne course. Congratulations to Dr. So!

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Why is this woman having left-sided weakness post Chiari decompression?

This 30-year-old female presents with left-sided weakness post Chiari decompression.

Q1 – What is the most likely diagnosis?

(a) Inadequate decompression
(b) Hydrocephalus with slit ventricles
(c) Pseudomeningocele
(d) Cerebellar ptosis
(e) Dandy-Walker continuum

Try to answer the question by looking at the first five images. Then, have a look at the latter five (images 6 through 10) duplicate images with arrows added for key findings.

Sagittal T1 FLAIR

Sagittal T1 FLAIR

Sagittal T1 FLAIR

Axial T1

Axial T1

Sagittal T1 FLAIR

Sagittal T1 FLAIR

Sagittal T1 FLAIR

Axial T1

Axial T1

 

A1 – (d) Cerebellar ptosis

When evaluating causes of failure of posterior fossa decompression in Chiari, it is important to systematically check that each of the following are NOT potential causes:

  • Insufficient posterior fossa decompression
  • Overvigorous decompression
  • Unrecognized hydrocephalus
  • Pseudomeningocele formation

Chiari decompression may be indicated if a syrinx is present and in situations where neurologic findings are present or in a sterotyped clinical presentation of tussive occipital or suboccipital headaches with syrinx. The goal of surgery is decompression of the cerebellar tonsils and opening of the CSF pathways at the skull base.

Decompression requires suboccipital craniectomy and often C1 laminectomy and may also include duraplasty sufficient to unblock the CSF pathways at the skull base. Overvigorous decompression above the equator of the cerebellum may result in downward migration of the cerebellum (ptosis) which may reproduce the obstruction at the skull base. This may result in recurrent symptoms and persistence, or re-expansion of a collapsed syrinx. This is a common but poorly appreciated cause of failure of Chiari surgery.

The failure to recognize that tonsillar displacement is secondary to increased intracranial pressure or an intracranial mass, and not a true Chiari, may also result in failed surgery. This is a serious error.

Pseudomeningocele occurs most commonly when duraplasty is performed but the repair breaks down or is not water tight.

Remember that any suspected Chiari malformation seen on a cervical spine MR should always prompt an examination of the brain for other causes of tonsillar displacement such as increased intracranial pressure or decreased intrathecal pressure (intracranial hypotension), the latter of which may cause tonsillar sagging.

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Reference:

1. Holly LT, Batzdorf U. JNS 2001 Jan: 94, 21-26.

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