|CASE IN POINT: ORTHOPEDIC RADIOLOGY
|Year : 2015 | Volume
| Issue : 1 | Page : 42-45
Parosteal lipoma of the foot: Radiological and correlative pathologic features
Neha Kharkwal1, Yatish Agarwal1, Rajni2, Brij Bhushan Thukral1
1 Department of Diagnostic Radiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
2 Department of Histopathology, Central Institute of Orthopedics, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
|Date of Web Publication||26-Oct-2015|
Dr. Neha Kharkwal
Department of Diagnostic Radiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kharkwal N, Agarwal Y, Rajni, Thukral BB. Parosteal lipoma of the foot: Radiological and correlative pathologic features. Astrocyte 2015;2:42-5
|How to cite this URL:|
Kharkwal N, Agarwal Y, Rajni, Thukral BB. Parosteal lipoma of the foot: Radiological and correlative pathologic features. Astrocyte [serial online] 2015 [cited 2022 Jul 3];2:42-5. Available from: http://www.astrocyte.in/text.asp?2015/2/1/42/168251
Lipomas are fairly ubiquitous benign neoplasm of adipose tissue origin, which can occur in any tissue or organ of the body. However, lipomas, which exhibit a contiguous relationship with the periosteum, are rather rare; termed as parosteal lipomas, they account for <0.1% of primary bone neoplasms and 0.3% of all lipomas.
We wish to report the radiological and correlative pathologic features in a rare case of parosteal lipoma of the foot, which presented clinically with a bony excrescence in a 33-year-old male. The patient had a gradually increasing painless swelling over the dorsomedial aspect of the left foot for the last 13 years. On clinical examination, the mass measured 9 cm × 6 cm and appeared to be twin-humped [Figure 1]. The mass had a firm to hard consistency and was fixed to the underlying bone. No associated neurodeficit or vascular compromise was observed. Systemic examination and laboratory findings were unremarkable. The mass was nontender and did not elicit any rise in local temperature, skin ulceration, or hyperemia. No history of trauma was elicited.
|Figure 1: Gross macroscopic appearance: Twin-humped nontender mass of 9 cm × 6 cm on the dorsomedial surface of the left foot.|
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His left foot radiograph revealed an irregular osseous protuberance contiguous with the first metatarsal bone and a well-circumscribed soft tissue mass [Figure 2]. Computed tomography (CT) foot demonstrated a whorl-like irregularly-marginated ossification arising from the dorsomedial and plantar aspects of the first metatarsal and medial cuneiform enveloped in a well-circumscribed multiseptated lobular mass of fat attenuation (Hounsfield value −87 to −120 HU) [Figure 3]a and [Figure 3] b. No medullary continuity could be demonstrated between the underlying bone and neo-ossification.
|Figure 2: AP and lateral radiograph of the left foot: Demonstrates an irregular osseous protuberance contiguous with the first metatarsal bone and a well-circumscribed soft tissue mass.
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|Figure 3: (a) Computed tomography of the left foot (bone window): Demonstrates a whorl-like irregularly-marginated ossification on the dorsomedial and plantar aspects of the first metatarsal and medial cuneiform. (b) Computed tomography of the left foot (soft tissue window): Demonstrates a well-circumscribed multiseptated lobular mass of fat attenuation (Hounsfield value −87 to −120 HU) enveloping the osseous mass.|
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The plain and contrast-enhanced magnetic resonance imaging (MRI), performed on 1.5 Tesla unit, demonstrated a well-marginated, multilobulated high signal intensity mass with several thin, low signal striations on the dorsomedial and plantar surfaces of the left foot [Figure 4]a. On the fat-suppressed sequence, almost the entire lesion showed a low signal intensity conversion representing fat [Figure 4]b. This was interspersed with intermediate signal intensity thin striations [Figure 4]c, which on contrast-enhanced T1 fat-saturated sequence showed minimal enhancement representing fibrovascular septa [Figure 4]d. The MR findings, bereft of enhancing solid nodules, were diagnostics of a benign lipomatous lesion.
|Figure 4: (a) T1 fast spin echo axial image of left foot: Demonstrates a well-defined, juxtacortical, hyperintense lesion (black arrow). The underlying bony excrescence is marked by a black asterisk. (b) STIR axial image of left foot: Demonstrates the suppression of the T1 and T2 hyperintensity connoting the fat component (black arrow). The bony excrescence is marked by a black asterisk. (c and d) T1 fat-saturated pre- and postcontrast coronal images of left foot: Showing suppression of the T1 hyperintensity indicating the fat component (black asterisk) interspersed with T1 intermediate signal intensity mildly enhancing fibrovascular strands.|
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On microscopic histological examination, the mass was composed of predominantly mature adipocytes interspersed with mature bony trabeculae [Figure 5]a. The finding was corroborated on the hematoxylin and eosin stained high power section, which demonstrated mature adipocytes with eccentric nuclei devoid of atypia [Figure 5]b, and was confirmatory of the diagnosis of parosteal lipoma.
|Figure 5: (a) Mature adipocytes interspersed with mature bony trabeculae (H and E, ×100) (b) Mature adipocytes with eccentric nuclei devoid of atypia (H and E, ×400).|
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| Discussion|| |
Parosteal lipomas are rare benign lipomatous masses, approximately 150 cases have been published so far in the English literature, which exhibit a contiguous relationship with the periosteum with an underlying osseous reaction. First described by Seering in 1836, the lesion was initially referred as "periosteal lipoma." The term "parosteal lipoma" was introduced by Power in 1888 in recognition of the juxtacortical position of the lesion.
These tumors are predominantly composed of adipose tissue and are frequently associated with chondroid, fibrous, and/or osseous changes, which permit their classification into four subtypes [Table 1].
The most common site is the femur, followed by the radius. Other rare sites where these lesions have been reported are tibia, fibula, humerus, scapula, clavicle, ribs, pelvis, metacarpals, mandible, and skull. Solitary metatarsal affliction is extremely rare with just a singular report in English literature.
Most patients present in the fifth–seventh decades with a classic history of a slowly growing, large, painless, nontender, immobile mass, not fixed to the skin., Occasionally, the mass may cause a neurological deficit when it is large or located such that it encroaches upon a nerve as in the proximal radius.
At gross pathologic examination, parosteal lipomas are lobulated greasy, yellowish masses, and intimately adherent to the underlying periosteum. They are composed of mature adult fat identical to soft tissue lipomas and are associated with underlying bony alterations, mostly hyperostotic reactive changes or osseous excrescences extending from and attaching the lesion to the underlying bone, and distinguishing parosteal lipoma from a soft tissue lipoma. These osseous excrescences do not show cortical or medullary continuity with the underlying bone. Cartilage and osteoid metaplasia typically occur adjacent to the osseous excrescences. The cytogenetic analysis has found the expression of reciprocal fusion transcripts of the HMGIC and lipoma preferred partner genes in parosteal lipomas. This is identical to the soft tissue lipomas, which are characterized by a 3; 12 translocation. This finding suggests a common histopathogenesis between lipomas of soft tissue and parosteal origin.
The imaging features of parosteal lipoma are usually distinctive. The radiographic features of parosteal lipoma are characterized by a juxtacortical radiolucent soft tissue mass with underlying reactive bony changes ranging from very subtle to obvious cortical thickening and variably sized ossific protuberances or excrescences. On bone scintigraphy, increased radiotracer accumulation is seen at the site of bone production.
The CT features of parosteal lipoma include the lipomatous component of the mass with attenuation values ranging between −60 and −125 HU, a variable degree of septation, intimate relationship of the mass to the underlying cortex, and underlying osseous reaction varying from mild cortical irregularity to well-defined osseous excrescence., The osseous excrescences may be composed of both cortical and marrow components, but without any continuity with the underlying bone, thus differentiating it distinctly from osteochondroma.
MRI best evaluates parosteal lipomas because of excellent soft tissue contrast and multiplanar imaging capability., The tumor presents as a juxtacortical mass with signal intensity identical to that of subcutaneous fat, with suppression of signal on fat-suppressed images. Heterogeneity corresponding to diverse pathological components is invariably present in the lesions. The cartilaginous components present as areas of intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images., Fibrovascular strands present as low signal intensity strands on T1-weighted images and higher signal intensity on the long TR images. The juxtacortical bony protuberance enveloped in lipomatous components and nerve entrapment leading to muscular atrophy are also well-identified, manifesting as increased fat in the involved muscle. Mild enhancement of the fibrovascular striations may be seen on contrast-enhanced CT and MRI.
Each parosteal lipoma must be duly evaluated for the possibility of a sarcomatous change. The presence of thick enhancing septa, nodular or globular enhancing soft tissue areas, decreased percentage of fat component, and invasion of surrounding structures are liable to reflect this change. However, until now, no reports of parosteal liposarcoma exist in the literature.
The treatment of a parosteal lipoma is complete surgical excision. The prognosis is excellent. Local recurrence is rare. In cases with nerve involvement, the tumor must be removed early before the setting of an irreversible muscular atrophy.
In conclusion, parosteal lipomas, although rare, must be considered in the clinical setting where a painless, nontender, and firm mass adherent to the bone exists. The distinctive imaging features, especially on MR, can clinch the diagnosis. Recognition is important as the lesion, though grotesque, lacks malignant potential and is eminently resectable.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]