Lipoma Arborescens in a 16-year old male: A case report
*aPaa Kwesi Baidoo, bFrank
Nketiah-Boakye, bEmile Kouakou Tano,aMajeedallahi Al-Hassan, bGaddiel
Obo Mensa Yorke, aRonald Awoonor-Williams,cErnest Boakye
Authors Affiliation:
aDirectorate of Orthopedics and Trauma, Komfo Anokye
Teaching Hospital, Kumasi, Ghana
bDepartment of Surgery, Komfo Anokye Teaching
Hospital, Kumasi, Ghana
Department of Pathology, Komfo Anokye Teaching Hospital, Kumasi, Ghana
Corresponding Author:
*Paa Kwesi Baidoo, MD
Directorate of Orthopedics and Trauma
Komfo Anokye Teaching Hospital
Kumasi, Ghana
Email:
pakvandal@gmail.com
ORCID:https://orcid.org/0000-0003-4028-1911
Funding: none declared
Conflict of Interest: None declared
Ethical approval:
Written informed consent was obtained from the legal guardian of the
patient for publication of this case report and the associated images.
Key clinical message
Lipoma arborecens though rare, should be considered as one of the many
differential diagnosis in children presenting with knee swelling and
chronic pain.
Abstract
Lipoma arborescens is a benign intra-articular tumor characterized by
joint effusions, pain and reduced range of motion. It is rare in adults
and children. We present a case of Lipoma arborescens in a 16 year old
male. The work up involved plain radiographs, MRI, incisional biopsy and
laboratory analysis.
Keywords:
Lipoma, arborescens, benign, tumor, intra-articular
Introduction
Lipoma arborescens (L.A) is an uncommon benign intra-articular lesion
consisting of villous synovial hypertrophy and proliferation of mature
fat cells.1 the term arborescens meaning “tree like”
in Latin, describes the unique villous and frond like appearance of this
condition.2 The knee is the most frequently involved
joint and mostly unilateral.3 The etiology is unknown
and usually presents in adults and is however rare in
children.4-8 Even though the condition is uncommon, it
should be considered as a differential diagnosis when patients presents
with chronic atraumatic knee pain and effusion.9 We
present a case of lipoma arborescens in the left knee of a 16-year old
boy and discuss the clinical and laboratory workup and subsequent
management.
Case Report
A 16-year old Ghanaian male presents to the outpatient clinic with a
5-year history of recurrent atraumatic left knee pain and swelling which
has worsened over the past one year. The pain was described as achy,
about 8/10 on the visual analog scale, and localized mainly in the
anteromedial and anterolateral aspect of the left knee. His symptoms
were aggravated by activity and was also associated with a limp and knee
stiffness. He did not have any pain in the left hip joint, groin or any
other joint and there was no history of injury to the left lower limb
previously. There has also not been any recent weight loss, anorexia,
fever or night pain.
On physical examination, he was afebrile, not pale and well nourished,
and had a body mass index of 25 kg/m2. The left knee
was swollen, tender and was associated with a 15cm by 15cm doughy mass
mostly localized to the suprapatellar region, that was not fixed to the
overlying skin or underlying structures. The distal pulses as well as
sensation were all intact and comparable to the contralateral limb. The
range of motion (ROM) in the left knee was 00 –
400 compared to 00 –
1400 in the right knee. There were not ligamentous
laxity.
X-rays of the left knee, and pelvis showing both hip joints were
obtained. The hips were essentially normal. X-ray of the knee showed
normal joint space, bony morphology and alignment, and no fractures or
dislocations. There was however an extensive soft tissue mass in the
suprapatellar region (Figure 1).
Laboratory test showed normal complete blood count (CBC), an elevated
erythrocyte sedimentation rate (ESR) of 45 mm/hour ( normal range – 0
to 15 mm/hour), normal values for C-reactive protein, rheumatoid factor
and anti-cyclic citrullinated peptides (Anti-CCP).
Magnetic resonance imaging (MRI) with and without contrast showed a
5.6cm x 8.8cm x 10.1cm heterogeneously enhancing lesion in the distal
third of the left thigh, predominantly anterior and deep to the rectus
femoris muscle. The lesion appeared isointense to the subcutaneous fat
on T2W, hyperintense on T1Pd and
suppresses on STIR. It also showed some areas of T1hypointensities and T2/STIR hyperintensities which
enhances post contrast. The lesion was seen to splay the adjacent
muscles with no obvious infiltration of the muscles (Figure 2). The MRI
was suggestive of liposarcoma and recommended a biopsy for confirmation.
All other structures in the knee were essentially normal.
The patient was worked up for an incisional biopsy following informed
consent from the legal guardian. The specimen was sent for
histopathology, the report of which indicated a lesion with focal
papillary- like fronts. The dominant cell types were matured fat cells
arranged in lobules. There were also areas with fibrous tissue and
myxoid changes as well as thick walled blood vessels within the lesion
and focal areas of synovial lining. This was consistent with lipoma
arborescens (Figure 3).
A total open synovectomy and excision of the hypertrophic multilobulated
yellowish white mass in the suprapatellar and medial recess was done 6
weeks later. The mass weight 200 grams and measured about 10cm by 10cm
(Figures 4a,b and c). The specimen sent for histopathology again was
consistent with lipoma arborescens. The patient was allowed to mobilized
on the left lower limb a day after the surgery and also commenced
physiotherapy to improve the range of motion of the left knee.
At 3 months follow up, the patient was able to fully flex and extend the
left knee with the range of motion been comparable to the right knee.
There was also resolution of the swelling and the knee pain.
Discussion
Lipoma arborescens is a very rare intra-articular lesion which is
characterized mainly by replacement of subsynovial tissue by matured fat
cells and fibrous tissues given the unique villous transformation of the
synovium into a tree-like pattern.1 The condition was
first described by Albert Hoffa, a German surgeon in 1904 and in 1957,
Arzimanoglu described the lesion in much
detail.10,11It commonly affects the
knee3 but there has been reported cases in the
shoulder12, elbow13,
wrist14, hip15 as well as in
synovial sheath and bursae which are
extra-articular.16
There has been fewer than 100 cases reported in the
literature17 of which fewer than 15 were in children,
making it extremely rare in this age group4,6-9. The
peak incidence is estimated to be between the third and fifth decades,
with a male predominance18. Sanamandra et al however,
did not observe any sex preponderance.2 Though the
etiology remains unknown, there has been reported association with
trauma, degenerative or inflammatory joint diseases.16
Lipoma arborescens can be classified as either primary or secondary
depending on the underlying condition or age of
presentation.19,20 The primary form of the lesion is
usually idiopathic and are found in younger patients aged between 20 and
30 years.16 The secondary form which is more common
and mostly seen in older patients is characterized by synovial
lipomatosis as a result of chronic irritation of the synovium secondary
to degenerative diseases, trauma, infections such as septic arthritis
and meniscal injury.2
Patients with LA can present as in our patient, with a slow progressive
swelling, recurrent joint effusion, restricted range of motion in the
affected joint, locking and pain without any history of trauma. On
physical examination, there may be joint effusion as well as a palpable
doughy mass mostly in the suprapatellar region.
Lipoma arborescens in the pediatric population should be differentiated
from other atraumatic chronic knee swellings such as juvenile rheumatoid
arthritis, Lyme disease, acute rheumatic fever, hemophilia, mycobacteria
tuberculosis, pigmented villonodular synovitis, synovial
osteochondromatosis and synovial hemangiomas. Complete blood count,
erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor,
Anti-CCP and screening for Lyme disease in endemic areas should be done
as part of the laboratory investigations to rule out the other
differential diagnosis though these are nonspecific.
Plain x-ray may show non-specific soft tissue swellings, bone erosions
and osteoarthritic changes in older patients.12,16 A
frond-like hyperechoic mass that waves during manipulation of the knee
is observed on ultrasound scan.21Computer tomography
(C.T.)scan may show a villous synovial mass the density of which is
similar to fat with no enhancement when contrast is
administered.17 MRI which is the imaging modality of
choice is used to differentiate LA with its peculiar appearance from
other intra-articular masses.16 It appears as a large
frond-like mass arising from the synovium, with similar signal intensity
as subcutaneous fat on all pulse sequence. 16 After
pre-saturation of the fat or signal suppression on short T1 inversion
recovery (STIR) sequence, the subsynovial portion shows a high signal
intensity on both T1 and T2 weighted images.12,19 With
the exception of the synovium layer and joint fluid which enhances due
to the presence of inflammatory cells, the mass does not show
enhancement with contrast.22 In addition to the
features above, there may be different degrees of joint effusion. These
characteristic features were all present in our patient.
Macroscopically, the lesion appears as a yellowish white mass with
frond-like pattern. Histologically, there may be papillary proliferation
of synovial villi and substitution of subsynovial tissue by mature fat
cells. The overlying synovium contains mononuclear infiltrate and
synovial cells are enlarged and reactive, with abundant eosinophilic
cytoplasm.3,12Lipoma arborescens is mostly treated
either by arthroscopic or open excisional biopsy depending on the extend
of the lesion and the surgeon’s personal experience. Recurrence after
surgical excision is uncommon.16
Conclusion
Lipoma arborescens is a rare intra-articular lesion that is
characterized by villonodular proliferation of the synovium. Its unique
appearance on MRI helps in differentiating it from other similar
conditions. It can be treated safely and effectively with either open or
arthroscopic synovectomy with a low risk of recurrence.
Acknowledgement:
Published with the written consent of the patient.
Conflict of Interest: None declared
Authors contributions:
PKB, MA,GOMY, RAW,FNB, EKT were directly involved in the surgery, follow
up and preparation of the manuscript. EB was responsible for reporting
on the histopathology and also preparation of the manuscript.
Ethical approval:
Written informed consent was obtained from the legal guardian of the
patient for publication of this case report and the associated images.
Data availability statement:
Data sharing is not applicable to this article as no new data were
created in this study.
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Figure legends:
Figure 1. Anteroposterior (AP) and lateral views of the left knee
showing normal bony appearance.
Figure 2. MRI images (coronal, sagittal and axial views) of the left
knee showing heterogeneously enhancing lesion predominantly anterior and
deep to the rectus femoris.
Figure 3. matured lipocytes arranged in lobules with areas of fibrous
tissues and myxoid changes (3a), thick walled blood vessel with thrombus
(3b) and associated synovial epithelium (3c).
Figure 4: Intra-operative pictures showing the lipoma arborescens in
situ (4 a and b) and the post excision lesion (4c).