Pseudotumoral lesions include a large & heterogeneous group of disorders and can be broadly classified1into following categories:
1. Normal anatomical variants.
2. Hamartomatous lesions:
Lipofibromatous hamartoma (LFH) of median nerve
3. Cysts and cyst like lesions;
Synovial cyst,
ganglion cyst and tendon sheath cyst
4. Infectious lesions:
5. Non infective- inflammatory lesions:
Inflammatory tenosynovitis,
Rheumatoid nodules,
Subcutaneous granuloma annulare,
Synovial osteochondromatosis.
Drug induced synovitis.
6. Post-traumatic lesions:
Epidermal inclusion cysts,
Myositis ossificans,
Foreign Body ( FB) granuloma,
Post-traumatic tenosynovitis / micro-vascular pseudo-aneurysm
7. Non-neoplastic vascular lesions
Hypothenar hammer syndrome
8. Metabolic disorders : (crystal deposition disease,
amyloidosis)
9. Miscellaneous disorders:
Nora’s lesion,
Palmar fibromatosis
a) Normal anatomical variants
Includes accessory muscles which may simulate masses with mass effect and thus can be symptomatic.
Extensor digitorum brevis muscle,
the extensor indicis proprius,
the accessory abductor pollicis minimi muscle and the anomalies of the flexor digitorum muscles (can cause ulnar / median nerve entrapment) are encountered accessory muscles of hand.
Ultrasound shows typical striated appearance of muscle and changes in shape with activity,
and follows muscle signal intensity on all pulse sequences of MRI1.
b) Cystic lesions:
Most common soft tissue pseudotumoral lesions of hand and wrist are cystic lesions accounting for 50-70% of all soft tissue tumors.
It includes ganglion cyst without synovial lining / synovial cyst with synovial lining (used interchangeably since it is not possible to differentiate these two entities on imaging),
tendon sheath cysts and hemorrhagic cysts2,
3.
Ganglion cyst: (Fig 1)
Cystic lesion with a dense fibrous connective tissue capsule lined with flat spindle-shaped cells.
Most common is peri-articular location with or without communication with joint.
Location: Most common location is dorsal aspect of wrist near scapholunate ligament,
followed by volar wrist near scapho-trapezial and radiocarpal joints and dorsal aspect of inter-phalangeal joints.
Most ganglion cyst are complex rather than simple -with well-defined margins,
thick walls,
locules,
thin septations and posterior acoustic enhancement on USG.
Communication with a joint or tendon sheath may be seen.
In case the cysts are deeper lying,
their relationship with the adjacent joint may not be detected.
A simple Ultrasonography (USG) with colour doppler can distinguish true cysts from pseudo cystic lesions like haemangiomas and vascular malformations.
Superimposed inflammation demonstrate peripheral color Doppler flow.
Ruptured ganglia (due to elevated pressure) may have a solid appearance and show increased doppler signal,
both central and peripheral.
Simple cyst follows fluid signal intensity on all MR sequences.( Fig1) Ruptured cysts are irregularly delineated and show pericapsular oedema on T2WI.
The ruptured cyst itself may show diffuse reactive enhancement with gadolinium contrast and non-enhancing pericapsular soft tissue oedema.
It is important to demonstrate communication with the joint space which has clinical implications during management.
If communicating with joint space,
stalk should be completely resected to avoid recurrence1,2,3.
Hemorrhagic cyst: Shows increased signal on T1 fat saturated images with peripheral enhancement.
Tendon sheath cyst: (Fig 2)
It is special type of ganglion cyst along the course of a tendon sheath arising from visceral layer or A1-A2 annular pulley of tendon sheath.
Etiology of this is unclear though trauma is considered as possible cause and should be differentiated from intratendinous cyst which can lead to rupture of tendon.
Both USG and MRI are effective in assessing these lesions.
Simple cystic lesion appears anechoic with post acoustic enhancement on USG,
hypointense on T1WI,
hyperintense on T2,
STIR sequences with no enhancement on contrast administration1,
2.
c) Infective lesions:
Most common mode of spread on infection is penetrating injury followed by hematogenous spread of the organism to the hand.
Following factors can predispose to hand infections such as diabetes mellitus,
alcohol consumption,
intravenous drug use,
gout,
steroids,
renal failure,
rheumatoid arthritis and peripheral vascular disease4.
Infectious tenosynovitis:
Tenosynovitis (Fig 3,
& Fig 4) is a closed-space pyogenic infection of the flexor (more common)/ extensor tendon sheath that can lead to tendon necrosis and rupture.
Flexor tenosynovitis of thumb and little finger can spread to the radial and ulnar bursa respectively and can spread across through the space of parona forming a horse-shoe shaped abscess.
Flexor tenosynovitis of the index,
middle,
or ring finger may rupture into the midpalmar space,
inturn involving the joint and bone4.
Synovial thickening with fluid along the tendon is seen on MRI with enhancement of synovium on post contrast study.
Minimal inflammatory changes can occur in the adjacent soft tissues.
Pustule:
Cellulitis is an infection of the subcutaneous tissues,
which might cavitate forming micro/macro abscess.
In some cases,
formation of pustule/ vesicle / blister(Fig 5) can occur following denudation4.
The pustule follows fluid signal on T2WI,
STIR,
intermediate / slightly hyperintense / hypointense on T1WI depending on the proteinaceous content.
Botryomycosis:
It is a chronic pyogenic granulomatous infection of skin (Fig 5) and rarely viscera.
Pulmonary involvement in botryomycosis is usually associated with skin involvement such as irregular masses,
sinuses.
Most common etiological agent is staphylococcus aureus followed by pseudomonas,
E.
coli,
proteus and streptococcus species.
History of trauma might precede symptoms.
Clinical features include nodules,
abscesses,
and sinuses with purulent discharge.
Differentials include mycetoma,
actinomycosis which affects larger area with discharge of sinuses and multiple fistulas5.
Our case (Fig 6 & Fig 7) had a well-defined,
pseudo-encapsulated lesion in the palmar aspect of the pulp of the middle finger of right hand with multiple tiny STIR hyperintense vesicles and intense post contrast enhancement.
The excision biopsy and culture proved it to be botryomycosis.
d) Inflammatory lesions:
Synovial chondromatosis:
It is of two types- based on etiopathogenesis.
Primary form ,
previously considered due to chondroid metaplasia of synovium of joint (intraarticular) / bursa / tendon sheath (extrarticular) resulting in the formation of chondral bodies,
is however now considered as benign neoplastic process.
Secondary form is associated with joint abnormalities,
mechanical/ arthritic disorders.
Primary synovial chondromatosis typically affects adults,
predominantly men,
in the third to fifth decades of life.
Tenosynovial or bursal chondromatosis most commonly affects adults over 20 years of age.
Radiograph shows radio dense bodies within the lesion representing calcified/ ossified loose bodies.
MRI shows hyperintense soft tissue signal intensity lesion along the radial bursa which appears hyperintense on T2/ STIR with multiple hypointense foci within the lesion representing osteochondral bodies6.
(Fig 8).
Drug - Ibandronate induced synovitis (Fig 9).:
Bisphosphonates are a widely used drug in patients with diseases associated with bone resorption (Paget’s disease of bone,
multiple myeloma,
hypercalcemia of malignancy,
and bone metastases).
However,
these drugs are noted to have many side effects because of its pro-inflammatory properties .
It is documented to cause synovitis (figure 6)/ polyarthritis / osteonecrosis of bone (nitrogen containing bisphosphonates).
IV administration is associated with more side effects compared with oral route of administration.
Patients with IV administration of bisphosphonates can present with bone pain,
myalgia,
arthralgia with or without flu-like symptoms with elevated ESR and CRP levels.
The withdrawal of bisphosphonates is the treatment of choice in these cases.
Alendronate should be considered as a possible cause of synovitis or polyarthritis in patients treated with this agent in the absence of any other pathology7.
(Fig 9).
Though literature citations of ibandronate induced synovitis are available,
our collection was able to document the MRI appearance of this rarer entity.
Generally associated systemic diseases and treatment related drug history will point towards the diagnosis of localized manifestations of the systemic disease .
Eg.
Synovitis in rheumatoid arthritis
e) Hamartomatous lesion :
Lipo-fibromatous hamartoma of median nerve:
LFH most commonly involves the median nerve though the reason for this predilection is unclear.
Chronic microtrauma from the carpal ligament or flexor retinaculum to median nerve has been suggested in pathogenesis.
LFH is due to benign overgrowth of fibrous and adipose tissue within a nerve sheath and is quite rare.
Clinically presents as a progressive palmar tumefaction and median nerve compression neuropathy during childhood.
Traumatic neuromas,
ganglion cysts,
lipomas and vascular malformations are the differentials to be considered.
On the axial and coronal images,
enlargement of median nerve and nerve fascicles can be seen ,due to fibrous and adipose tissue overgrowth.
This has been described as ‘cable-like’ appearance on axial,
spaghetti like on coronal images and is pathognomonic for LFH8.
(Fig 10).
f) Post traumatic lesions :
Skin lesions - Epidermal inclusion cyst:
Clinical history plays an important role in the diagnosis of epidermal inclusion cyst with history of trauma and entrapment of epidermal fragments into the deeper tissues by trauma or an iatrogenic injury.
The most common sites are nail bed,
subcutaneous plane and intradermal planes.
MR shows a well-circumscribed lesion of fluid signal which varies,
depending on the amount of internal keratin debris (Fig 11).
Lack of central enhancement with peripheral enhancement is characteristic finding of epidermal cysts that helps in distinguishing these lesions from neurogenic tumors or sarcomas.
If present close to the tendon sheath,
it can be confused with ganglion cysts9,10.
Hematoma: (Fig 12)
Hematomas can occur in patients with anticoagulant therapy/ coagulopathy disorders following trauma.
Clinical features include pain,
swelling and ecchymosis at the site of injury and hematoma.
Signal intensity on MRI depends on age of hematoma as follows; T1,
T2 iso/hypointense if acute,
T1 and T2 hyperintense if subacute and T1,
T2 hyperintense with hypointense wall due to either hemosiderin/ fibrous tissue in chronic stage.
If enhancing soft tissue nodules are present within the hematoma with no antecedent history,
underlying tumors should be ruled out11.
Accidental injection of hydraulic material with foreign body reaction :
Accidental injection of water,
wax,
paint thinner,
cement,
plastic,
oil,
and hydraulic fluid have also been reported.
These materials under high pressures (2,000-10,000 psi),
can pass across gloves into the tissues resulting in injury.
Severity of injury depends on type and amount of injected material,
site of injury,
duration lapsed after injury before treatment etc.
Tamponade effect and direct toxicity of injected material can result in ischemia12.
Penetrating injury can result in infection in addition to foreign body injection. Clinical features include swelling,
redness,
pain,
abscess formation etc.
Our case (Fig 13 & 14) had a history of accidental injection of hydraulic oil. Multiple foci of dark signal intensity on post contrast GRE sequences noted in both palmar and dorsal aspects of hand – representing hydraulic oil droplets foreign material with magnetic susceptibility .
Peripheral enhancement with non-enhancing central necrotic area representing abscess seen.
There is extension of cellulitis to sub-aponeurotic plane and into the palmar aspect of hand,
tracking through 3rd intermetacarpal space upto deep space of parona..
Associated underlying 4th metacarpal osteomyelitis changes noted (fig 13& Fig 14).
Foreign body resulting in vascular injury and pseudoaneurysm: (Fig 15 & Fig 16)
Penetrating injury by foreign bodies may result in localized cellulitis changes and if infected can cause abscess.
If the foreign body is sharp and injures vascular structures,
it might cause vessel wall disruption,
resulting in pseudoaneurysms.
Etiological factors for vascular pseudoaneurysm,
in addition to trauma include iatrogenic vascular procedures,
percutaneous biopsy/ drainage,
anastomotic disruption and intravenous drug abusers.
Clinical features includes pulsatile mass,
palpable thrill and audible to and fro murmur ,
if the pseudoaneurysm is large in size.
Imaging findings in gray scale USG includes cystic structure with or without communication with adjacent artery and eccentric mural thrombus.
Doppler examnation shows typical swirling motion called the “yin-yang sign”.
To and Fro movement within the communicating channel between sac and artery on Doppler is more characteristic.
Hyperdense/ hypodense sac like structure in the vicinity if the arteries is seen on plain CT and contrast filled sac with or without filling defect (thrombus) usually communicating with the adjacent artery is seen on contrast-enhanced CT.
CT angiogram being the gold standard,
has advantages of shorter acquisition time,
non-operator dependency and demonstration of associated injuries.
In patients with contrast allergy or renal failure,
MRI can be advocated.
Management includes USG guided compression,
USG guided thrombin injection,
cathether based intraluminal procedures or surgical repair13,
14.
Our case (Fig 15 ) of penetrating injury in the palmar aspect of thenar eminence of right hand had ill-defined inflammatory changes involving subcutaneous plane, intermuscular plane and extending along the 2nd slip flexor tendons. Dynamic post contrast MR angiography revealed post- traumatic pseudo aneurysm in the princeps pollicis branch of radial artery in the thenar eminence.
Without the dynamic contrast study,(Fig.16) the tiny pseudoaneurysm,
from a branch of radial artery ,
might have been missed.
Meticulous high resolution imaging with dynamic contrast study is particularly important in small focal lesions and in traumatic injuries,
to assess the associated vascular involvement,
thereby prompting appropriate management.
h)Non- neoplastic vascular lesions:
Non Venous ectasia with venous thrombus15:
This study documents an interesting case that presented with a subcutaneous nodule at distal part of fourth and fifth metacarpal,
close to volar crease in the superficial soft tissue,
with T1,
T2,
STIR hypointense band in the 4th intermetacarpal space.
Histopathologically the lesion turned out to be venous ectasia with venous thrombosis(Fig 17).
Such vascular lesions,
especially with no significant antecedent history,
when complicated by associated organized sub-acute thrombus can be difficult to diagnose in MRI,
because of the reactive enhancement of the thrombus that may mimic a tumour.
This case was reported as a possible neoplastic lesion,
and as always,
HPE gave the final diagnosis.
i) Palmar Fibromatosis
Dupuytren’s contracture:
It is a fibrosing disorder,
primarily involving palmar aponeurosis and its extensions,
resulting in flexion contractures of the fingers.
They are usually diagnosed based on clinical history and physical findings and has a recurrence of ~30-40% after surgery.
Clinical presentation: Patients typically present with palmar surface subcutaneous nodules on the distal crease of the hand,
which may progresses to cords and bands and finally,
the characteristic flexion contractures develop,
secondary to fibrous attachments to the underlying tendon sheath.
Imaging features includes subcutaneous nodules at the level of distal palmer crease, Hypointense cords (on both T1 and T2 WI) lie parallel and superficial to flexor tendons.
(Fig 18 & Fig 19).
Cellularity of the cord has prognostic value,
which correlate with the T1 and T2W signal intensity. Isointense signal with muscle represent highly cellular cord.
These cords on histology are mitotically active,
cellular and have the highest recurrence rates (70%).
Darker fibrotic cords are hypocellular and are least likely to recur16.
Localized superficial fibromatosis:
The superficial (fascial) fibromatoses arise from fascia or aponeuroses at palmar,
plantar,
penile (Peyronie disease),
and knuckle pad locations.
Superficial fibromatoses vary from low- (higher collagen) to-intermediate (higher cellularity) T1 and T2-weighted signal intensity depending on lesion cellularity.
-A heterogeneous lesion (well-defined or ill-defined) with non enhancing low signal intensity bands on all pulse sequences is highly suggestive of fibromatosis17.
(Fig 20)
J) Miscellaneous disorders:
Bizarre paraosteal osteochondromatous lesions:
Nora’s lesion also called as bizarre parosteal osteochondromatous proliferation (BPOP) is a rare and benign osteochondromatous exostosis which is locally aggressive and often recurrent (50%) arising from the bony cortex.
(Fig 21). These lesions most commonly arises from small bones of hands,
feet and less commonly in long bones,
maxilla and skull and is painful.
Most common age group is young (20-30 year old) patients.
The major challenge for radiologists is differentiating this lesion from radiologically similar conditions,
both benign (myositis ossificans - has a centripetal pattern of ossification,
Turret exostosis and florid periostitis) and malignant (parosteal osteosarcoma or chondrosarcoma).
Imaging features may be nonspecific,
histology is essential for definitive diagnosis.
Histology (Fig.22)showing hypercellular cartilage with maturation to trabecular bone along with frequent spindle-shaped chondrocytes interspersed in the intertrabecular spaces.
A distinct blue tinctorial appearance to the bone may be helpful in distinguishing the lesion from parosteal osteosarcoma18.