DOI:10.2214/AJR.07.2589
AJR 2008; 190:582-588
© American Roentgen Ray Society
Imaging Appearance of Diffuse Neurofibroma
Douglass S. Hassell1,
Laura W. Bancroft1,
Mark J. Kransdorf1,2,
Jeffrey J. Peterson1,
Thomas H. Berquist1,
Mark D. Murphey2,3 and
Julie C. Fanburg-Smith4
1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC.
3 Departments of Radiology and Nuclear Medicine, Uniformed Services University
of the Health Sciences, Bethesda, MD.
4 Department of Soft Tissue Pathology, Armed Forces Institute of Pathology,
Washington, DC.
Received May 16, 2007;
accepted after revision September 26, 2007.
Address correspondence to D. S. Hassell
(dshassell{at}gmail.com).
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army or the Department of Defense.
Abstract
OBJECTIVE. The purposes of this study were to describe the imaging
appearance of diffuse neurofibroma in 10 patients and to summarize demographic
data on a large group of patients.
MATERIALS AND METHODS. Retrospective review of the pathology and
radiology teaching databases at two institutions yielded the cases of 339
patients with a pathologic diagnosis of diffuse neurofibroma.
Diagnostic-quality images were available for 10 patients. Images from MRI
(n = 8), CT (n = 5), and sonographic (n = 1)
examinations were evaluated for lesion location, size, depth of involvement,
growth pattern, and intrinsic signal intensity, attenuation, or echogenicity.
Demographic information, associated lesions, and tumor location were recorded
for all patients.
RESULTS. Among 10 patients with images, eight of whom had
neurofibromatosis, diffuse neurofibroma involved the skin and subcutaneous
tissues (n = 9) and frequently extended to the fascia over muscle
(n = 6). Plaquelike (n = 5) and infiltrative (n =
3) growth patterns were most common. One lesion had a mixed growth pattern.
Prominent internal vascularity was common (n = 5). MRI signal
intensity and CT attenuation were typically nonspecific. Enhancement was
intense in all five patients with contrast-enhanced MR examinations. Including
patients with and those without images, 349 diffuse neurofibromas were present
in 339 patients. The mean patient age was 35.1 years. Lesions involved the
extremities (n = 120), trunk (n = 122), head and neck
(n = 98), and deep structures (n = 9).
CONCLUSION. Diffuse neurofibroma frequently grows as a plaquelike or
infiltrative lesion involving the skin and subcutaneous tissues. Prominent
internal vascularity is common. There is a much wider soft-tissue and age
distribution and association with neurofibromatosis than previously
reported.
Keywords: diffuse neurofibroma • neurofibromatosis
Introduction
Neurofibroma is common, representing approximately 5% of all benign
soft-tissue tumors in large surgical series. Three types of neurofibroma are
classically described: localized, diffuse, and plexiform
[1,
2]. The localized variety is
the most common, representing approximately 90% of these lesions, and is the
subtype most familiar to radiologists because its imaging appearance has been
well documented. The plexiform subtype is essentially pathognomonic of
neurofibromatosis 1 (NF1) and also is well reported.
Diffuse neurofibroma is an uncommon subtype of neurofibroma that has
received little attention in the imaging literature. It has been reported to
occur most commonly among children and young adults, typically involving the
skin and subcutaneous tissues of the head and neck
[3–7].
NF1 has been reported in only a minority of patients with diffuse neurofibroma
[1,
3,
6–9].
Unlike other types of neurofibroma, which have a masslike pattern of growth,
diffuse neurofibroma is a poorly defined lesion that spreads along connective
tissue septa and surrounds rather than destroys adjacent normal structures
[1,
3,
6,
7]. Surgical excision is not
mandatory because malignant transformation is rare
[2]. Resection is performed
when the tumor is severely disfiguring or severely compromises function
[10]. Complete resection is
often difficult because of the extensive and infiltrative nature of many of
these lesions [2,
3,
8,
10].
The scant literature on the imaging features of diffuse neurofibroma
consists of scattered case reports
[1,
5,
8–10].
In the largest case series to date
[11], investigators examined
the sonographic findings of diffuse neurofibroma in seven patients. As are
most superficial lesions, diffuse neurofibroma is often evaluated clinically.
If biopsy is needed, it is usually performed without imaging. The extent of
large lesions may have to be determined with cross-sectional imaging. The pur
pose of this study was to retrospectively examine the imaging features of
pathologically proven diffuse neurofibroma to define the typical radiologic
features. We also reviewed demographic and pathologic data on a large group of
patients with diffuse neurofibroma to better define the spectrum of patient
presentations, including age and sex, anatomic distribution of the lesions,
and the existence of comorbid conditions.
Materials and Methods
The study was conducted in accordance with the requirements of our
institutional review board. In accordance with the requirements for a
retrospective study, informed consent was not required. Retrospective searches
were conducted of the pathology and radiology teaching databases at two
institutions to identify cases of pathologically proven diffuse neurofibroma.
One database covered 1994–2006 and the other 1960–2006. Inclusion
criteria were confirmed pathologic diagnosis of diffuse neurofibroma, known
lesion location, and availability of the demographic information on patient
age and sex. A total of 339 patients met these criteria. In addition, we
identi fied a subset of 10 patients with diagnostic-quality MR, CT, and/or
sonographic images of diffuse neuro fibroma. In all cases, the diagnosis of
diffuse neuro fibroma was made in accordance with pre viously described
pathologic features and criteria
[6] (Fig.
1A,
1B).
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Fig. 1A —31-year-old man with neurofibromatosis. Histologic features
of diffuse neurofibroma. Photomicrograph shows diffuse neurofibroma cells with
short fusiform and round shapes present within fine fibrillary collagen
background (black arrows). Scattered fat cells (white
arrows) are present.
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Fig. 1B —31-year-old man with neurofibromatosis. Histologic features
of diffuse neurofibroma. Photomicrograph shows multiple laminated bodies
(arrows) that resemble Wagner-Meissner tactile corpuscles and are
characteristic of diffuse neurofibroma.
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Demographic data were available on all 339 patients in the study group and
included age and sex. Lesion location and associated pathologic diagnoses were
determined from pathology reports. Lesion location was classified as head and
neck, trunk, extremity, or deep. The head and neck classification included all
structures of the head and neck region, both superficial and deep. The trunk
consisted of the skin, subcutaneous tissues, fascia, and muscles of the chest,
abdomen, and pelvis. The shoulder and hip regions were considered part of the
trunk. The deep classification included all intrathoracic, intraabdominal, and
intrapelvic structures (e.g., posterior mediastinum, lung apex, bladder, and
mesentery).
Four musculoskeletal radiologists working in consensus reviewed diagnostic
examinations of the subset of 10 patients who had MR, CT, or sonographic
images or a combination of these images. Lesion size was measured, and maximal
dimension recorded. When a lesion extended beyond the entire field of view, a
maximal dimension was estimated. For analysis, lesions were subdivided by size
into three groups: smaller than 5 cm, 5–15 cm, and larger than 15 cm.
The dominant growth pattern was classified as plaquelike, infiltrative,
masslike, or mixed. A plaquelike growth pattern was assigned to lesions that
appeared as a thick slab of abnormal tissue without interposed noninvolved
tissue. The maximal thickness of these lesions was measured. Lesions with
poorly defined margins and areas of interposed uninvolved tissue were defined
as infiltrative. The masslike growth pattern was assigned to lesions with
well-defined margins and a roughly round or ovoid appearance. A mixed growth
pattern displayed features of more than one primary growth pattern. The
presence of involvement of skin, subcutaneous fat, fascia, muscle, and other
tissues was assessed. Internal vascularity was subjectively established if
vessels were clearly identified within the lesion on MRI, CT, or
sonography.
Eight MRI examinations were available for eight patients. Lesion signal
intensity was evaluated on T1-weighted, T2-weighted, and contrast-enhanced
T1-weighted images. On T1-weighted images, signal intensity was defined
relative to skeletal muscle and fat. Non-fat-suppressed T2-weighted images
(spinecho, fast spin-echo, and turbo spin-echo sequences) were available for
five of the eight patients who had MR images. Fat-suppressed T2-weighted
images were available for the other three patients. Because of the variability
in T2-weighted sequences, lesion signal intensity was determined relative to
skeletal muscle. Gadolinium-enhanced images were available for five patients,
and enhancement was subjectively defined as absent, mild, moderate, or
intense. Images from five CT examinations were available for five patients.
Three patients had undergone unenhanced imaging, and two had undergone
contrast-enhanced imaging. Both unenhanced and contrast-enhanced CT scans were
evaluated for lesion attenuation relative to skeletal muscle, and the lesions
were defined as having low attenuation, similar attenuation, or high
attenuation. If a diffuse neurofibroma exhibited fat attenuation, this finding
was noted. Sonographic images were available for one patient and had been
obtained at biopsy. A lesion was defined as hypoechoic, isoechoic, or
hyperechoic on the basis of its echogenicity compared with adjacent normal
tissues.
Results
MRI, CT, and Sonographic Imaging Features
The imaging group included five male and five female patients (mean age,
40.6 ± 19.1 [SD] years; range, 13–69 years)
(Table 1). Neurofibromatosis 1
(NF1) was present in seven patients and neurofibromatosis 2 (NF2) in one
patient. The mean time between imaging and pathologic diagnosis was 7.3 months
(range, 0–24 months). Imaging preceded pathologic diagnosis in all 10
cases. Diffuse neurofibromas were distributed on the trunk (n = 6),
head and neck (n = 3), and extremities (n = 1). Lesions were
typically large, most being larger than 15 cm (n = 5) or between 5
and 15 cm (n = 4). Only one lesion was smaller than 5 cm (n
= 1).
A plaquelike pattern of growth was dominant in five lesions. The mean
plaque thickness was 2.5 cm (Fig.
2A,
2B). Skin and subcutaneous
tissue involvement was present in all five plaquelike diffuse neurofibromas.
Extension to the fascia overlying muscle was present in two of five plaquelike
lesions. Deep extension into the left orbit was present in one patient (Fig.
3A,
3B,
3C). One plaquelike gluteal
lesion was associated with a large hematoma in the subcutaneous tissues.
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Fig. 2A —65-year-old man with plaquelike diffuse neurofibroma.
Sagittal T1-weighted MR image (TR/TE, 500/16) shows thick plaquelike diffuse
neurofibroma involving skin and subcutaneous tissues of back. Deep aspect
(black arrow) of mass is well-defined, and deeper subcutaneous
tissues are uninvolved. Small flow voids (white arrows) reflect
prominent internal vascularity.
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Fig. 2B —65-year-old man with plaquelike diffuse neurofibroma.
Sagittal T2-weighted MR image (3,200/104) shows diffuse neurofibroma
(white arrows) is markedly hyperintense in relation to muscle
(black arrow).
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Fig. 3A —24-year-old man with plaquelike diffuse neurofibroma of left
temporal region with intraorbital extension. Axial T1-weighted MR image
(TR/TE, 350/16) shows plaquelike diffuse neurofibroma extending from left
temporal (thick arrow) to nasal region. Mass extends into orbit
(thin arrow).
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Fig. 3B —24-year-old man with plaquelike diffuse neurofibroma of left
temporal region with intraorbital extension. Axial T2-weighted MR image
(2,926/80) shows diffuse neurofibroma (arrows) to be mildly
hyperintense in relation to muscle but of overall intermediate signal
intensity.
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Fig. 3C —24-year-old man with plaquelike diffuse neurofibroma of left
temporal region with intraorbital extension. Axial contrast-enhanced
T1-weighted MR image (400/19) shows prominent enhancement of diffuse
neurofibroma (arrows).
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Three lesions had an infiltrative growth pattern as opposed to the more
common plaquelike growth pattern (Fig.
4A,
4B). Two infiltrative lesions
were centered in the subcutaneous fat with extension to overlying skin and
fascia overlying muscle. The third infiltrative lesion did not involve the
skin or subcutaneous tissues and originated in the vastus medialis muscle
above the left knee. All infiltrative lesions contained macroscopic fat, which
in one case suggested a diagnosis of liposarcoma.
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Fig. 4A —31-year-old woman with diffuse neurofibroma of left lateral
buttock region shows infiltrative growth pattern. Axial T1-weighted MR image
(TR/TE, 650/11) shows infiltrative diffuse neurofibroma (arrow)
centered within subcutaneous tissue of left lateral buttock region.
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Fig. 4B —31-year-old woman with diffuse neurofibroma of left lateral
buttock region shows infiltrative growth pattern. Axial contrast-enhanced
T1-weighted MR image (550/12) with fat saturation shows enhancement of
infiltrative diffuse neurofibroma with extension to skin (thick
arrow) and fascia (thin arrow) overlying right gluteal
musculature.
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One diffuse neurofibroma manifested as a mass centered in the subcutaneous
tissues of the right frontal region (Fig.
5A,
5B). One final diffuse
neurofibroma had a mixed growth pattern (Fig.
6A,
6B,
6C). This diffuse neurofibroma
involved the skin and subcutaneous tissues in a plaquelike manner and the
entire gluteus maximus muscle in an infiltrative manner without destroying the
overall morphologic features of the muscle.
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Fig. 5A —20-year-old man with masslike diffuse neurofibroma of right
frontal region. Axial fat-suppressed T2-weighted MR image (TR/TE, 2,200/80)
shows diffuse neurofibroma (arrow) to be mildly hyperintense in
relation to skeletal muscle (seen on other axial images) or of overall
intermediate signal intensity.
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Fig. 5B —20-year-old man with masslike diffuse neurofibroma of right
frontal region. Coronal contrast-enhanced T1-weighted MR image (500/17) with
fat saturation shows intense enhancement of diffuse neurofibroma
(arrow).
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Fig. 6A —62-year-old woman with diffuse neurofibroma of right buttock.
Axial T1-weighted MR image (TR/TE, 467/9) shows plaquelike thickening of skin
(thin white arrow) of right gluteal region, which is slightly
hyperintense in relation to muscle. At deep aspect of skin thickening, diffuse
neurofibroma becomes more infiltrative (thick white arrow). Diffuse
neurofibroma extends to and infiltrates right gluteus maximus muscle
(black arrow), which is markedly enlarged.
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Fig. 6B —62-year-old woman with diffuse neurofibroma of right buttock.
Axial contrast-enhanced T1-weighted MR image (594/10) with fat saturation
shows diffuse infiltration and marked enlargement of gluteus maximus muscle
(arrow) with maintenance of overall muscle structure.
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Fig. 6C —62-year-old woman with diffuse neurofibroma of right buttock.
Sonographic image obtained during biopsy of diffuse neurofibroma shows mixed
sonographic appearance. Superficial subcutaneous portion (black
arrow) of mass is hyperechoic with small irregular hypoechoic areas. Deep
intramuscular portion (white arrow) of mass is hypoechoic.
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Overall, skin and subcutaneous tissues were involved by nine of 10 diffuse
neurofibromas. There was extension to the fascia overlying muscle in six cases
and involvement of structures deep to the fascia in two cases. Prominent
internal vascularity was present in five lesions (Fig.
2A,
2B).
On T1-weighted MR images, signal intensity was similar to (n = 4)
or mildly higher than (n = 3) that of skeletal muscle. In one case,
the lesion was nearly isointense to fat. On T2-weighted images, lesions were
either mildly (n = 4) or markedly (n = 4) hyperintense to
skeletal muscle. Enhancement was intense in all five patients for whom
contrast-enhanced T1-weighted images were available.
Attenuation on the unenhanced CT scans of three patients varied from lower
than that of skeletal muscle (n = 1) through similar to that of
skeletal muscle (n = 1) to similar to that of fat (n = 1).
In the last case, the lesion of nearly fat attenuation had internal
reticulations with attenuation similar to that of skeletal muscle. The diffuse
neurofibroma had similar attenuation to muscle in one of two patients with
contrast-enhanced CT scans. In the second patient with contrast-enhanced
images, the lesion had reticulations with attenuation similar to that of
skeletal muscle with areas of interposed fat attenuation. Absolute enhancement
of diffuse neurofibroma on CT could not be determined because no patient had
both unenhanced and contrast-enhanced images.
Sonographic images were available for one patient, in whom the diffuse
neurofibroma had a mixed growth pattern
(Fig. 6C). The superficial
portion of the diffuse neurofibroma exhibited plaquelike involvement of the
skin and subcutaneous tissues. This portion of the lesion was hyperechoic with
multiple irregular hypoechoic areas. The deep infiltrative portion of this
diffuse neurofibroma involved the entire gluteus maximus muscle and was
diffusely hypoechoic.
Demographic Data
The demographic group consisted of 159 (47%) male and 180 (53%) female
patients. The mean age was 35.1 ± 18.2 years (range, 1–94 years).
The incidence of neurofibromatosis among the patients without images was
unknown because the historical records on neurofibromatosis were incomplete. A
total of 349 diffuse neurofibromas were identified in the 339 patients. Lesion
distribution included the extremities (n = 120, 34%), trunk
(n = 122, 35%), head and neck (n = 98, 28%), and deep
structures (n = 9, 3%) (Fig.
7). No additional pathologic lesion was identified in 306 (88%) of
the patients. Thirty-four (10%) of the lesions were mixed plexiform and
diffuse neurofibroma and were identified in 34 patients. Underlying malignant
lesions were present in nine (3%) of the diffuse neurofibromas in nine
patients. Among these tumors were four malignant peripheral nerve sheath
tumors, one dermatofibrosarcoma protuberans, one angio sarcoma, one
neuroectodermal tumor, and two malignant tumors that were not otherwise
specified.
Discussion
Diffuse neurofibroma is a relatively rare tumor that has been reported to
occur primarily in children and young adults
[3–7].
The wide age range of patients in our study, however, serves to redefine this
demographic characteristic, as does the expanded scope of soft-tissue
involvement. Although it has been previously described as the most typical
site
[3–8],
the head and neck region accounted for only 28% of all lesions in our series.
Trunk and extremity lesions were more common, each accounting for slightly
more than one third of all diffuse neurofibromas.
The incidence of neurofibromatosis among patients with diffuse neurofibroma
has been reported to be approximately 10%
[6]. Although the incidence of
neurofibromatosis in our entire study population is unknown, seven of the 10
patients in the imaging subset had NF1. Another patient had NF2. These
findings and those of Megahed
[12] suggest an increased
incidence of NF1 among patients with diffuse neurofibroma. Some authors
[3,
4] have speculated that the low
reported incidence of NF1 among patients with diffuse neurofibroma may be
related to difficulty in diagnosing NF1 in young patients. That the mean age
of the imaging patients in our study was 41 years, clearly beyond the
child–young adult age group identified by others as the most common
cohort with diffuse neurofibroma, may be evidence of a greater association
with neurofibromatosis.
In the small number of patients in whom an associated lesion was identified
at pathologic examination, plexiform neurofibroma was found in 34 (79%) of 43
instances. Because plexiform neurofibroma is strongly associated with NF1, the
association between diffuse neurofibroma and NF1 may be stronger than
previously thought. Underlying malignancy, most commonly a malignant
peripheral nerve sheath tumor, was present in 3% (9/349) of the lesions in our
series. This low incidence of associated malignancy is concordant with the
belief that malignant transformation of diffuse neurofibroma is rare
[3,
4].
Most diffuse neurofibromas were isointense or mildly hyperintense in
relation to muscle on T1-weighted images and mildly or markedly hyperintense
to muscle on T2-weighted images. These signal intensity characteristics are
similar to those described in previous case reports
[5,
8,
9]. Intense enhancement on
contrast-enhanced images was the rule and has been reported previously
[5,
9]. Prominent internal
vascularity was also a common finding in our study and has been previously
reported [8,
9].
Although the signal intensity was not specific, the pattern of growth was
quite characteristic of diffuse neurofibroma. Skin and subcutaneous tissue
involvement was most typical. Extension to fascia overlying muscle and to
deeper tissues was less common. A plaquelike growth pattern was present in
five of 10 patients and was most characteristic. This pattern was previously
described by de Varebeke et al.
[5] in a case report of diffuse
neurofibroma of the neck. Microscopic analysis has shown that diffuse
neurofibroma is known to infiltrate the dermis and subcutaneous tissue, often
extending along connective tissue septa
[1,
3,
6,
7]. The imaging appearance of a
plaquelike mass therefore is not unexpected.
Three diffuse neurofibromas in our study had an infiltrative growth pattern
with internal areas of macroscopic fat. This infiltrative growth pattern is
another presentation of diffuse neurofibroma. The appearance of two of these
lesions was similar to that described by Huang et al.
[1]. The internal macroscopic
fat within the two infiltrative subcutaneous diffuse neurofibromas seen at
imaging most likely represented preserved subcutaneous fat within tissue
infiltrated by the diffuse neurofibroma. The third diffuse neurofibroma with
macroscopic fat arose within the vastus medialis muscle. The amount of fat
within this lesion was greater than would be expected even in the setting of
complete atrophy or fatty replacement of the muscle. Mesenchymal elements,
including mature fat and ectatic vessels, have been reported to be associated
with neurofibromatous tissue
[6]. The presence of the
mesenchymal fat may account for the appearance of this diffuse
neurofibroma.
In our study, imaging preceded pathologic diagnosis in all 10 cases.
Detailed information on clinical decision-making at initial presentation was
available for only two patients. In these two cases, the diagnosis of diffuse
neurofibroma was not initially entertained clinically. In one case, diffuse
neurofibroma was prospectively suggested on the basis of the imaging features
of the lesion, namely, its plaquelike growth pattern. In the other cases, we
had incomplete information regarding the clinical decision-making at imaging
and image-guided or surgical biopsy.
Sonography has been increasingly used in the evaluation of soft-tissue
masses, including diffuse neurofibroma. Wide availability, lack of ionizing
radiation, cost-effectiveness, and speed of examination are advantages of
sonography. Sonography, however, can be limited in assessment of the extent of
large lesions and in discerning lesion margins. Chen et al.
[11] reported on the
sonographic features of diffuse neurofibroma. All seven diffuse neurofibromas
in their study were located in the subcutaneous fat zone, and all were
hyperechoic masses permeated by multiple interconnecting irregular hypoechoic
tubular or nodular structures. Sonographic images, obtained at the time of
biopsy, were available for a single patient in our imaging subset. The
subcutaneous plaquelike portion of this diffuse neurofibroma with a mixed
growth pattern had sonographic features similar to those described by Chen et
al. The deeper, infiltrative portion, however, was diffusely hypoechoic,
differing from the subcutaneous diffuse neurofibromas described by Chen et al.
It is difficult to draw conclusions from a single case, but perhaps the
sonographic appearance of deeper tissue (e.g., muscle) involvement differs
from that of subcutaneous tissue involvement. More study is needed into the
sonographic appearance of deep involvement by diffuse neurofibroma.
Limitations of this study include its retrospective nature, small number of
patients with relevant images, and variability of the imaging protocols among
patients. Lack of information regarding clinical decision-making at imaging
and biopsy and about the surgical procedures performed are additional
limitations. Nonetheless, we believe the patient demographics, lesion
locations, pathologic subtype information, and imaging findings are revealing.
Diffuse neurofibroma affects a wider age range of patients than previously
believed, and there is a more even distribution of cases among the head and
neck, trunk, and extremities. The incidence of underlying malignancy
associated with diffuse neurofibroma is low, but the association with
neurofibromatosis is likely greater than previously reported.
Imaging features most suggestive of diffuse neurofibroma include a
plaquelike or infiltrative pattern of growth involving the skin and
subcutaneous tissues, prominent internal vascularity, and marked contrast
enhancement. In our experience, few lesions manifest with the combination of
plaquelike growth, prominent internal vascularity, and marked enhancement, and
these features in particular are strongly suggestive of diffuse neurofibroma.
Although the imaging experience with this lesion is too limited for the
conclusion that the plaquelike appearance is pathognomonic of diffuse
neurofibroma, this appearance is quite characteristic. Cutaneous lymphoma and
hemangioma, in some instances, are two additional differential considerations.
The infiltrative growth pattern, in contrast, is nonspecific. Nonneoplastic
conditions such as cellulitis and hemorrhage can manifest in this manner and
are much more common than diffuse neurofibroma. Angiomatous lesions such as
hemangioma, angiolipoma, and angiomyolipoma also can mimic the infiltrative
appearance of some diffuse neurofibromas.
As are most superficial lesions, diffuse neurofibromas are often evaluated
clinically; if pathologic diagnosis is needed, biopsy is often performed
without imaging. Imaging may be needed to determine the extent of large
lesions and those suspected of having deeper extension. Cross-sectional
imaging, including MRI, CT, and sonography, is well suited to defining the
extent of disease, and the findings may suggest the diagnosis of diffuse
neurofibroma before pathologic confirmation.
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Abstract
Introduction
