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Histological findings in resected leiomyomas
following MR-HIFU treatment, single-institution
data from seven patients with unfavorable focal
therapy
Antti Viitala, Michael Gabriel, Kirsi Joronen, Gaber Komar, Antti
Perheentupa, Teija Sainio, Jutta Huvila, Pekka Pikander, Pekka Taimen &
Roberto Blanco Sequeiros
To cite this article: Antti Viitala, Michael Gabriel, Kirsi Joronen, Gaber Komar, Antti
Perheentupa, Teija Sainio, Jutta Huvila, Pekka Pikander, Pekka Taimen & Roberto Blanco
Sequeiros (2023) Histological findings in resected leiomyomas following MR-HIFU treatment,
single-institution data from seven patients with unfavorable focal therapy, International Journal
of Hyperthermia, 40:1, 2234666, DOI: 10.1080/02656736.2023.2234666
To link to this article:  https://doi.org/10.1080/02656736.2023.2234666
© 2023 The Author(s). Published with
license by Taylor & Francis Group, LLC.
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Histological findings in resected leiomyomas following MR-HIFU
treatment, single-institution data from seven patients with unfavorable
focal therapy
Antti Viitalaa, Michael Gabrielb, Kirsi Joronenc, Gaber Komara, Antti Perheentupac, Teija Sainiod, Jutta Huvilae,
Pekka Pikandere, Pekka Taimene and Roberto Blanco Sequeirosa
aDepartment of Radiology, University of Turku and Turku University Hospital, Turku, Finland; bInstitute of Biomedicine, University of Turku,
Turku, Finland; cDepartment of Obstetrics and Gynecology, University of Turku and Turku University Hospital, Turku, Finland; dDepartment
of Medical Physics, University of Turku and Turku University Hospital, Turku, Finland; eDepartment of Pathology, University of Turku and
Turku University Hospital, Turku, Finland
ABSTRACT
Purpose: Magnetic resonance – high-intensity focused ultrasound (MR-HIFU) is a noninvasive treat-
ment option for symptomatic uterine leiomyomas. Currently, pretreatment MRI is used to assess tissue
characteristics and predict the most likely therapeutic response for individual patients. However, these
predictions still entail significant uncertainties. The impact of tissue properties on therapeutic out-
comes remains poorly understood and detailed knowledge of the histological effects of ultrasound
ablation is lacking. Investigating these aspects could aid in optimizing patient selection, enhancing
treatment effects and improving treatment outcomes.
Methods and materials: We present seven patients who underwent MR-HIFU treatment for leio-
myoma followed by second-line surgical treatment. Tissue samples obtained during the surgery were
stained with hematoxylin and eosin, Masson’s trichrome and Herovici to evaluate general morphology,
fibrosis and collagen deposition of leiomyomas. Immunohistochemical CD31, Ki-67 and MMP-2 stain-
ings were performed to study vascularization, proliferation and matrix metalloproteinase-2 protein
expression in leiomyomas, respectively.
Results: The clinical characteristics and radiological findings of the leiomyomas prior to treatment as
well as qualitative histological findings after the treatment are presented and discussed in the context
of current literature. A tentative model for volume reduction is presented.
Conclusion: These findings provide insights into potential factors contributing to suboptimal thera-
peutic outcomes and the variability in histological changes following treatment.
ARTICLE HISTORY
Received 10 April 2023
Revised 15 June 2023
Accepted 4 July 2023
KEYWORDS
MR-HIFU; MR-guided
high-intensity focused
ultrasound; histology;
uterine fibroid; leiomyoma
Introduction
Magnetic resonance – high-intensity focused ultrasound (MR-
HIFU) is a therapeutic option for symptomatic uterine leio-
myomas [1]. During treatment, absorbed ultrasound induces
rapid tissue temperature elevation to approximately 60–
70 
C. Over the following months, a reduction in leiomyoma
volume and symptom improvement have been observed in
most but not all cases [2,3]. The underlying mechanisms con-
tributing to shrinkage, or lack thereof, are not fully under-
stood. Although rare, lack of sufficient treatment response is
a potential clinical problem and necessitates a second-line
treatment. In this paper, we report our observations of such
cases. We review existing literature and describe the histo-
logical and radiological findings in seven MR-HIFU-treated
patients who underwent second-line surgical treatment due
to insufficient treatment outcomes.
Characteristics of uterine leiomyomas
Structure and ECM
Uterine leiomyomas are firm, stiff, nodular tumors consisting
of smooth muscle cells (SMCs) and extracellular matrices
(ECMs) [4]. Leiomyomas have a well-defined outline and are
surrounded by a pseudocapsule consisting of compressed
muscle fibers [5]. Leiomyomas grow mostly from their per-
iphery, which has more mitosis (during the secretory phase),
apoptosis (during the proliferative phase) and a higher blood
vessel density than their central parts [5–7].
Leiomyomas have an excessive amount of ECM when
compared with myometrium. The ECM of the leiomyoma tis-
sue consists mainly of collagen, fibronectin and proteogly-
cans. Collagen type I is the most abundant and is expressed
in larger quantities compared to the myometrium [8,9].
Compared to the myometrium, collagen fibrils in leiomyomas
CONTACT Antti Viitala antti.j.viitala@gmail.com Department of Radiology, University of Turku and Turku University Hospital, Kiinamyllynkatu 4-8, 20521
Turku, Finland
Supplemental data for this article can be accessed online at https://doi.org/10.1080/02656736.2023.2234666.

 2023 The Author(s). Published with license by Taylor & Francis Group, LLC.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted
Manuscript in a repository by the author(s) or with their consent.
INTERNATIONAL JOURNAL OF HYPERTHERMIA
2023, VOL. 40, NO. 1, 2234666
https://doi.org/10.1080/02656736.2023.2234666
are more abundant, shorter, loosely packed and unorganized
[4]. Collagen in the leiomyomas is entirely extracellular [4].
Procollagens and other molecules needed to form the
ECM are synthesized by cells and secreted into the interstitial
space, where they undergo further processing and self-
assembly into the ECM. Individual collagen molecules bundle
together to form a microfibril, which in turn cross-links to
form collagen fibers. Fibronectin binds to collagen, proteo-
glycans and other ECM components creating a complex scaf-
fold of molecules. Proteoglycans contain highly hydrophilic
components that retain water molecules in ECM and contrib-
ute to the overall physical structure of tissues. They also pro-
vide co-receptors and storage sites for growth factors stored
within the ECM [10–12].
Once formed, the ECM is actively remodeled by regulated
processes of degradation and regeneration. Excessive
amounts of ECM in leiomyomas are apparently caused by
both the overproduction of collagen and a decrease in
remodeling and breakdown processes. The ECM interacts
with SMCs via mechanotransduction; cells’ internal cytoskel-
eton is attached to the ECM by integrin molecules of the cell
membrane, through which the cell receives mechanical cues
related to environmental conditions such as stretch and pres-
sure. SMCs of leiomyomas appear to have an attenuated
response to mechanical stimulus [11–13].
Matrix metalloproteinase (MMP) enzymes are involved in
ECM degradation. MMPs are expressed in SMCs in an inactive
form and are secreted into the interstitial space where they
are activated. Among the various MMPs, the concentration of
MMP-2 is significantly higher in leiomyomas. MMP-2 is
known to have the widest target molecule spectrum and is
involved in the degradation of both native and denatured
collagen. When the ECM is degraded by MMPs, growth factor
molecules stored within the ECM may be released and able
to bind to SMCs, promoting their proliferation [11,12,14].
Growth and development of leiomyoma
Two intertwined processes are involved in the growth of
leiomyomas: the formation of excess SMCs and the produc-
tion of excess ECM. These are understood to be promoted
by mechanotransduction, hormonal signaling and growth
factors [12].
Despite the above-mentioned molecular similarities, the
composition of the leiomyomas varies considerably. This is
seen in properties such as the cellularity, stiffness (elasticity),
amount of ECM, and density of vasculature [15]. Mechanical
stiffness of the leiomyoma appears to correlate with the
amount of ECM and how organized the collagen within the
ECM is [4]. The mechanical stiffness may also be related to
the interstitial fluid influencing the properties of glycosami-
noglycans in the ECM [13] or changes in the relative amount
of different collagen types [8]. While SMCs respond to hor-
monal changes, ECM collagen fibrils are not affected by the
menstrual cycle [4]. As leiomyomas grow, they undergo
degenerative processes such as hyaline degeneration, fatty
degeneration, cystic degeneration, myxoid degeneration,
hemorrhagic necrosis and calcification [16–18]. After
menopause, a reduction in leiomyoma cell size and overall
size is generally observed [19].
MRI characteristics
On MRI, T2-hypointense leiomyomas typically have higher col-
lagen content, mass density, stiffness, water content and cellu-
larity [20–22]. T2-hyperintense leiomyomas tend to have
higher cellularity with little collagen or extensive degenerative
changes [22,23]. An increase in T2 intensity also correlated
with higher proliferative activity [24]. Degenerated leiomyomas
tend to have a heterogeneous appearance [16,20,23].
In T1w gadolinium-enhanced MRI (T1gdþ), cellular leio-
myomas tend to show homogeneity and high enhancement
at 30–90 s, whereas degenerated leiomyomas tend to show
irregular, peripheral or minimal enhancement. ‘Ordinary’ leio-
myoma showed irregular, peripheral or minimal enhance-
ment while areas with extensive hyaline degeneration show
low enhancement [25].
Ultrasound ablation
Acoustic energy transmitted via ultrasound waves is
absorbed by the tissue and transformed into thermal energy,
thereby inducing rapid local temperature elevation.
Histologically, reported changes include coagulation necrosis,
hemorrhagic necrosis and hemorrhage [26,27]. For other tis-
sue types such as the liver, thermal fixation [28–31], boiling
or cavitation, and collapse of tissue architecture have been
reported, especially at higher ultrasound intensities. When
the resected leiomyomas were ablated ex vivo, coagulation
necrosis with preserved tissue architecture was observed in
the ablated areas [32].
Radiologically, post-treatment non-perfused volume (NPV)
is generally observed [2,33]. Post-treatment NPV often
exceeds the ablated area, perhaps owing to the spread of
apoptotic mediators [2,27], interruption of vascular supply
[27] and underestimation of the extent of thermal dose.
Coagulation necrosis
Traditional morphological characteristics of tissue necrosis
include an increase in cell volume, swelling of organelles,
and rupture of cell membranes, leading to the loss of intra-
cellular contents [34]. Coagulative necrosis may occur as a
result of heating or ischemic injuries.
Thermal fixation
Thermal fixation of heated tissue has been reported in the
liver parenchyma [29,30], prostate gland [28] and myome-
trium [35], suggesting that it could occur in HIFU-treated
leiomyoma. Thermal fixation tends to occur in regions receiv-
ing higher thermal doses than in areas that undergo coagu-
lation necrosis [30,35]. Thermal-fixed tissue is characterized
by cell death combined with preservation of tissue architec-
ture and nuclei [29,30,35]. Nuclei preservation is likely a con-
sequence of the hyperthermic inactivation of intracellular
enzymes participating in normal breakdown processes.
2 A. VIITALA ET AL.
Thermally fixed regions appear to resist normal tissue break-
down, perhaps secondary to the thermal denaturation of
proteins, which might lead to foreign body reactions.
Reabsorption of tissue debris is inhibited, and a giant cell
reaction can be observed at the periphery of the zone.
Cellular staining properties of thermally fixed tissue have
been reported to fade over time, while tissue architecture is
preserved, resulting in characteristics mimicking coagulative
necrosis [35].
Thermal changes in collagen
As the ECM is heated, denaturation of collagen is feasible at
temperatures and time spans encountered during MR-HIFU
[10]. Some changes in the collagen structure may be revers-
ible, but at higher temperatures irreversible changes occur
[10]. The denaturation rate is known to depend on tempera-
ture, mechanical load, hydration, chemical environment and
amount of cross-linking (maturity) [10]. Ex vivo bovine ten-
dons, which have high collagen content, shrink when heated
[36]. The amount of shrinkage depends on the temperature
and exposure time, while the proportion of denatured colla-
gen fibrils increases with shrinkage [36]. Despite the initial
shrinking, heat-treated tendons lose their mechanical
strength and become easier to stretch [36]. Typical shrinkage
temperature of mammalian collagens is known to be around
65–67 
C [37].
Vessel occlusion
Intentional targeting of the main arteries of leiomyomas is
technically viable, resulting in devascularization extending
much further than the original ablated area [38]. Even with-
out intentional targeting, NPV is routinely observed to
extend beyond the targeted volume. Pathological features in
the ischemic area should resemble those encountered fol-
lowing uterine artery embolization (UAE), namely necrosis,
calcification and vascular thrombosis [39].
Ultrasound ablation: delayed effects
In an early trial, when seven patients underwent hysterec-
tomy within one month of treatment, pathological findings
included coagulative necrosis and hemorrhage [27,40]. In a
series of 12 patients who underwent second-line surgical
treatment at a median time of seven months, the most com-
mon histological finding was infarction-type necrosis sur-
rounded by granulation tissue, concomitant with the
infiltration of lymphocytes and macrophages [41]. It has
been proposed that either apoptosis mediators or their
impact on the local vasculature could spread and extend the
initial area of necrosis [2,27,33]. Changes in mechanotrans-
duction-mediated signaling or the hormonal environment
also seem feasible.
Leiomyoma shrinkage
Most leiomyoma volume reduction occurs during the first six
months, followed by slower volume reduction over the next
few years [2,3]. At six months, the volume of the NPV is
reported to shrink by approximately 70% regardless of the
T2 intensity of the leiomyoma tissue. While in the remaining
perfusing part of the leiomyoma, the volumetric change is
reported to range from 25% (T2-hypointense tissue) to
þ42% (T2-hyperintense tissue) [2].
There is still a poor understanding of the processes, which
contribute to the shrinkage of leiomyomas. Hypotheses pre-
sented so far include apoptosis [33], phagocytosis [33],
breakdown and absorption of necrotic tissue [42], healing of
the thermal injury [33], replacement of necrotic tissue with
other tissue types such as granulation and scar tissue,
changes in local hormonal activity, immunological response,
changes in local vasculature, or a combination of multiple
processes. One of our aims was to add to the limited data
available on these processes. Despite shrinkage, some
residual NPV usually remains in situ months after treatment,
and possibly permanently [42].
Materials and methods
Potential candidates were referred from hospitals around
Finland and recruited for the ongoing clinical trial
(NCT02914704). Ethics approval was obtained from the
Hospital District Ethics Committee (approval #
ETMK:95/1801/2015 16.6.2015). The patients underwent
screening by a gynecologist, followed by MRI. A multidiscip-
linary team discussed each treatment decision. Informed con-
sent was obtained from all the participants. Therapies were
conducted using the Profound Medical Sonalleve V2 MR-HIFU
device (SW version 3.5.1271.1817) on a Philips Ingenia 3.0T
MR system. Patients were followed up through gynecology
visits, symptom severity score questionnaires, and MRI.
In the cases reported here, surgical intervention was
selected as the second-line treatment (Table 1) and included
two myomectomies and five hysterectomies (two by morcel-
lation). Myomectomy or hysterectomy specimens were
placed in formalin in the operating room and embedded in
paraffin after 24 h fixation. Tissue sections were cut at 5 mm
thickness. Initial staining was performed using either Van
Gieson’s or hematoxylin and eosin (H&E) staining. After iden-
tifying the relevant samples, further staining was performed
with H&E, Masson’s trichrome (MTri) and Herovici.
Immunohistochemical staining was performed using CD31,
Mib-1 and MMP-2 antigens. Details of the staining protocol
are given in the supplementary material.
Histological slides were digitized using a 3DHISTECH
Pannoramic 250 scanner (3DHISTECH Ltd., Budapest,
Hungary). Image analysis was conducted using the QuPath
v.0.2.0m8 [43]. QuPath’s cell detection functionality was used
to calculate the number of cell nuclei per mm2 (cell density,
CD), which was used to identify the pixels containing extra-
cellular collagen from MTri staining and pixels containing
CD31þ cells. The proportion of these areas compared to the
overall surface area was calculated (collagen%, CD31%).
While platelets and some immune cells are CD31-positive,
the majority of CD31þ cells are endothelial cells lining blood
INTERNATIONAL JOURNAL OF HYPERTHERMIA 3
vessels. Therefore, CD31% was used as an indication of histo-
logically confirmed vasculature.
MRI characteristics on T2 were categorized according to
the Funaki classification [33] and T1gdþ according to the
classification described by Mindjuk et al. [44].
Results
Patient characteristics and procedural outcomes
Although all treated myomas were Funaki type II, there were
considerable variations in their gadolinium uptake, CD,
collagen% and CD31% (Figure 1, Table 1). The median non-
perfused volume percentage (NPV%) immediately post-treat-
ment was 37% (Table 2). No HIFU-related complications
occurred in any of the patients. Median tumor shrinkage con-
firmed by MRI at the time of surgery was 31%. The reasons for
second-line surgical treatment included insufficient clinical
symptom improvement (N ¼ 6), the appearance of new leio-
myoma (N ¼ 1) and low initial NPV% (N ¼ 1).
Cases without histologically confirmed necrosis
Case 1
A large leiomyoma (848ml) showed heterogeneity in the
pretreatment T1gdþ image. Owing to poor heating, the
patient underwent two HIFU treatments, resulting in an
NPV% of 37% and a leiomyoma volume reduction of 9% at
three months. As the clinical response was insufficient, lap-
aroscopic hysterectomy was performed at 13 months. In the
gross pathology section, leiomyoma was soft and disinte-
grated, containing a cavity filled with a gel-like substance.
Histologically, tissue structure degeneration was observed at
the rim of the liquefied cavity while no necrotic areas were
observed (Figure S1).
Case 2
Although the tissue heated well, the NPV% was only 9% owing
to anatomical constraints. A shrinkage of 48% and complete
disappearance of the NPV were observed at six months.
Hysterectomy was performed due to insufficient clinical
improvement. No necrotic areas or other tissue changes were
identified in the histological samples (Figure S2).
Case 4
The patient had a single 59ml intramuscular leiomyoma. In
T1gdþ, the myoma was hyperintense to the myometrium
during the arterial phase and hypointense during the venous
phase, indicating very rapid gadolinium wash-in and wash--
out. The heating was poor. Based on simulations, high perfu-
sion and the deep location of the myoma were identified as
the most plausible explanations for poor heating [45]. At
post-treatment T1gdþ, a good NPV% was observed during
the arterial phase, which then decreased to a minimum of
3% during 10-min dynamic scanning. Hysterectomy was per-
formed at one month. In the gross pathology section, the
leiomyoma tissue appeared hemorrhagic. The tissue was
highly cellular, highly vascularized and contained practically
no collagen (Figure S4).
Cases with histologically confirmed necrosis
Histological necrosis corresponding to the treated regions
was observed in four cases (cases 3, 5, 6 and 7). In each
case, we observed regions of dense scarred tissue, consisting
of highly organized collagen bundles mixed sparsely with
basophilic nuclei (Figure 2(a)). Sparse Mib-1þ and MMP-2þ
cells were observed in the collagenous material. In case 7,
few blood vessels were observed within the dense scarred
tissue region. In all cases, the scarred region shared a bound-
ary with remaining leiomyoma tissue (Figure 3).
In cases 3 and 5, we observed a central region of non-
organized coagulative necrosis (Figure 2(b)). These regions
were characterized by preserved tissue architecture, that is,
EMC with empty cell compartments of approximately the
same size as the cells in the surrounding leiomyoma tissue,
and unorganized collagen bundles roughly corresponding to
the size and shape of the collagen bundles of the surround-
ing leiomyoma tissue. Hematoidin deposits were present,
indicating that hemoglobin had undergone metabolism
under low-oxygen conditions. Remnants of blood vessels
Table 1. Patient characteristics.
Age Myoma Funaki (T2) classification Mindjuk (T1gdþ) classification Symptoms Medication
Case 1 46 y 898ml
Submucosal
Type II, homogeneous Type II, heterogeneous Pain and pressure at lower
abdomen
–
Case 2 38 y 95ml
Subserosal
Type II, homogeneous Type III, heterogeneous Abdominal pressure, urinary
frequency
–
Case 3 32 y 21ml
Intramural
Type II, heterogeneous Type III, homogeneous Infertility, deformation of the
uterine cavity due to
leiomyoma
Ulipristal acetate prior HIFU
Case 4 40 y 59ml
Intramural
Type II, homogeneous Type II homogeneous
(venous phase)
Type III homogeneous
(arterial phase)
Hypermenorrhea leading to
anemia
Combined oral contraceptive
post HIFU
Case 5 41 y 242ml
Intramural
Type II, homogeneous Type II, homogeneous Hypermenorrhea, urinary
urgency
Ulipristal acetate prior HIFU,
hormonal IUD prior and
post HIFU
Case 6 38 y 170ml
Intramural
Type II, homogeneous Type III, homogeneous Hypermenorrhea Ulipristal acetate prior HIFU
Case 7 41 y 361ml
Intramural
Type II, homogeneous Type II, homogeneous Urinary frequency Ulipristal acetate post HIFU
4 A. VIITALA ET AL.
lined with CD31þ endothelial cells were also present. Mib-
1þ and MMP-2þ cells were not detected. In both cases,
regions with non-organized coagulative necrosis shared a
boundary with the dense scarred regions, which in turn
shared a boundary with remaining leiomyoma tissue. In case
3, the dense collagenous area was organized as a one to four
mm thick scar-like rim surrounding the central area of coagu-
lative necrosis (Figure S3), at the periphery of the heating
effect. For other cases, the maximal thicknesses of the dense
scarred regions on histology slides were 10, 9 and 3mm.
Figure 1. Pretreatment MR-images. Histological samples are from the regions of the remaining leiomyoma tissue. CD: collagen% and CD31% show heterogeneous
histology. Scale bar applies for all histological images.
INTERNATIONAL JOURNAL OF HYPERTHERMIA 5
Boundary area
For cases 3 and 6, the transition between collagenous tissue
type and untreated leiomyoma tissue was sharp (Figure 3).
In cases 5 and 7, a transition layer (approximate width
0.4mm) was observed, which was characterized by a
decreased density of myocytes and increased collagen. No
increase in Mib-1þ, CD31þ or MMP-2þ cells was observed
at the boundary. In Herovici staining, collagen appeared to
be mature. In case 3, few macrophages and lymphocytes
were observed close to the boundary. No foreign body or
giant cell reaction was observed in any case.
Discussion
In the present study, we report on the histological and radio-
logical findings of seven HIFU-treated leiomyomas with insuffi-
cient primary outcomes leading to second-line surgical
treatment. The median post-treatment NPV% of reported cases
was lower than those typical for HIFU patients at our clinic [46],
which is consistent with findings that the re-intervention rate
increases when NPV% decreases [42]. Histological samples of
remaining leiomyoma tissue after treatment had heterogeneous
characteristics. In particular, the collagen% varied considerably
between patients, which could impact ultrasound absorption,
tissue heating and post-treatment processes of clearing tissue
debris. It is unclear whether the hyaline degeneration observed
in case 1 was preexisting. Case 4 had exceedingly high cellular-
ity and perfusion, which explains both the poor heating and
rapid tissue healing post-treatment.
Regions of non-organized coagulative necrosis (cases 3 and
5) are readily explained as remnants of the original tissue archi-
tecture. These findings are compatible with either ischemia or
thermal coagulation necrosis as the primary processes, although
thermal fixation cannot be ruled out. Hematoidin deposits and
CD31þ remnants of the endothelium confirm that the remains
are a vestige of the original tissue architecture.
Regions of dense scarred tissue are best explained by the
formation of new scar tissue post-treatment surrounding the
treated central area. This is supported by the high degree of
organization in the region. The presence of Mib-1þ and
MPP-2þ cells is compatible with metabolic activity, although
perfusion of blood vessels was only observed in case 7. The
Herovici staining of the region did not differ from that of
other areas, indicating similar maturity. Scar formation could
explain the observed post-treatment leiomyoma growth, at
least in some cases. As an alternative hypothesis, these
regions could represent the original tissue that has under-
gone necrosis, from which all other tissue components
besides extracellular collagen have been cleaned by
immunological processes. However, the high degree of colla-
gen fiber organization and the absence of hematoidin
deposits do not support this hypothesis.
At the boundaries of collagenous and leiomyoma tissue,
no signs of active immunological reaction or collagen
processing were observed. Possibly, such processes existed
post-treatment, but had reached a steady state before the
samples were obtained.
Our study is limited by the fact that histological findings
represent only a single time point for each patient; therefore,
processes leading to findings and their causality to the treat-
ment can only be hypothesized. The patient population was
intentionally selected based on the need for second-line sur-
gical treatment and was not representative of patients gen-
erally. Four of the seven patients used ulipristal acetate, and
two of the patients hormonal contraception either before or
after HIFU, possibly confounding the results.
Model for volume reduction
Based on literature and our findings, we can hypothesize
possible mechanisms behind post-treatment volume reduc-
tion and symptom improvement. As the tissue is heated, cell
membranes are broken, ECM proteins undergo denaturation,
Table 2. Procedural outcomes.
HIFU procedure Initial NPV
Leiomyoma volume
change post-therapy Reason for surgery Surgery
Case 1 Poor tissue heating at therapy
time, response varied at
different areas
37% (after two
HIFU procedures)
9% at 3 months Insufficient clinical
response
13 months post HIFU,
laparoscopic hysterectomy
Case 2 NPV limited by surrounding
bowel loops
9% 48% at 6 months Insufficient clinical
response
7 months post HIFU,
hysterectomy
Case 3 Heats well 36% 38% at 10 months Continued uterine cavity
deformation and
infertility, appearance
of new leiomyomata
10 months post HIFU,
laparoscopic myomectomy
Case 4 Highly vascularized
leiomyoma, poor heating
despite using maximum
power 300 W
3% Follow-up imaging
not done
Low NPV 1 months post HIFU,
hysterectomy
Case 5 50% 24% at 12 months Insufficient clinical
response
29 months post HIFU,
laparoscopic hysterectomy
using morcellation
Case 6 Heats well 54% 22% at 3 months Insufficient clinical
response
19 months post HIFU,
laparoscopic myomectomy
Case 7 45% 42% at 3 months Symptom recurrence at
one year
16 months post HIFU,
laparoscopic hysterectomy
with morcellation
6 A. VIITALA ET AL.
Figure 2. (a) Samples from regions with dense scarred tissue. Organized collagen bundles mixed sparsely with basophilic nuclei are seen. Few blood vessels are pre-
sent in case 7. Scale bar applies for all images. (b) Samples from regions with non-organized coagulative necrosis. Original tissue architecture is preserved, empty
cell compartments and unorganized collagen bundles are seen. Hematoidin deposits and remnants of blood vessels are present. Scale bar applies for all images.
INTERNATIONAL JOURNAL OF HYPERTHERMIA 7
and perfusion ceases. Consequently, the ability of the tissue
to retain water diminishes, and some of the initial volume
reduction is likely due to the loss of fluid content. Stiffness
can be reduced either by the loss of fluid content or the
direct thermal changes of tissue components, especially in
the ECM. Subsequent enzymatic dismantling of denaturated
structures by MMPs and phagocytosis are conceivable,
although we did not find any direct evidence for this. In
Figure 3. Boundary of remaining leiomyoma tissue and dense scarred tissue. No increase of Mib-1þ, CD31þ or MMP-2þ cells is seen at the boundary. In Herovici,
staining collagen appears mature.
8 A. VIITALA ET AL.
some cases, dismantling the structures seems impossible, as
remnants of the original tissue architecture are seen. This
inability could be secondary to the denaturation of the con-
stituent molecules, especially those of the ECM. The forma-
tion of dense scarred regions observed here could be an
attempt to encapsulate and isolate the remnants of necrotic
tissue. There is, however, variation, as evidenced by case 2,
where, despite high collagen%, NPV had completely disap-
peared within six months. In highly cellular leiomyomas with
low collagen% (such as case 4), problems with ECM disman-
tling are likely smaller, and remnants of the SMCs might be
removed from the site by phagocytosis, or they could remain
in situ and transform into (hyaline) degeneration.
In many cases, ischemia extending beyond the heated
region has been observed. The processes occurring in such
ischemic regions probably differ from those occurring in the
actual treatment area, potentially resulting in distinct MRI
and histological characteristics. As ischemic regions are
known to shrink following UAE therapies, a similar outcome
would be expected after HIFU treatment as well.
As previously discussed, shrinkage of the remaining per-
fused leiomyoma tissue may occur post-treatment. This
could be explained by changes in mechanotransduction,
hormonal environment or immunological processes affect-
ing untreated regions. On the other hand, an increase in
leiomyoma volume could be attributed to the continuous
growth of remaining leiomyoma tissue and scarification
processes.
Among the weaknesses of this study, low number of
patients has to be mentioned. This is primarily due to the
low re-intervention rates in our center. Reported cases
include only patients where a second-line surgical interven-
tion was required, and therefore are not representative of all
HIFU-treated patients. On the other hand, these are the
patients we are most interested in since the effect of the pri-
mary treatment was not sufficient. Although the number of
cases reported here is too low for statistical analysis, we
hope that our observations can provide insights to guide
future studies.
Acknowledgements
We want to thank the Histocore unit of the University of Turku, Auria
Biopankki and the Finnish Institute for Health and Welfare for their
assistance with the samples.
Disclosure statement
The authors report there are no competing interests to declare.
Funding
AV reports that his work was partially supported by personal grants
from the Radiological Society of Finland and the University of Turku.
Data availability statement
Data are made available on reasonable request.
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