Keywords
Hyaluronic acid - gluteal augmentation - filler injections - magnetic resonance imaging
Introduction
Hyaluronic acid (HA) is a widely accepted agent most commonly used as a dermal filler
in facial aesthetic/cosmetic medicine.[1]
[2] Its main benefits include maintaining a youthful appearance, through facial rejuvenation
and volume restoration secondary to aging or even post-traumatic facial disfiguration.[1]
[2]
[3] More recently, and as HA products continue to develop, attention has turned to the
use of HA for body contouring and more specifically gluteal augmentation.[4] The common side effects of HA injection (HAI) are often minor and self-limiting.[5]
[6] HA migration is a rare complication, and there is lack of literature about HA migration
following gluteal augmentation.
We report a rare case of HA buttock injection (HAI) migration in a transgender patient.
The aim is to create awareness among radiologists to allow early detection and management
of such unusual radiological imaging findings.
Case Report
A 41-year-old man undergoing gender change to female of South-East Asian ethnicity
was referred to our department for an ultrasound scan (USS) following a 6-week history
of an unprovoked progressively enlarging palpable painless mass on the medial aspect
of her right thigh. She was otherwise asymptomatic, fit, and well, without any significant
past medical history. She did, however, mention that she had undergone a recent gluteal
augmentation procedure as a part of her transgender transition, in a private clinic.
The gluteal augmentation was performed using HA gel fillers; however, the patient
was not entirely sure about the specific HA agent utilized.
On examination, the patient had a painless fluctuant mass on the medial aspect of
her right thigh, with no associated erythema or any other signs suggestive of an infection.
The mass was mobile and measured 6.6 by 1.7cm.
The patient had an USS of the mass that demonstrated a subcutaneous homogeneously
hyperechoic lesion with no vascularity of Doppler imaging ([Fig. 1]). The sonographic features were similar to that of fat and hence an initial diagnosis
of subcutaneous lipoma was made.
Fig. 1 Ultrasound scan. Longitudinal view of mass in medial right thigh within the subcutaneous
compartment and superficial to the deep fascia. The mass is homogeneously isoechoic
relative to the surrounding subcutaneous fat. No vascularity was demonstrated on Doppler
imaging.
Given the nonspecific findings, a magnetic resonance imaging (MRI) of the pelvis and
thigh was performed. On MRI, the mass was found to be continuous with smaller foci
of identical signal in the posterior and lateral aspect of the thigh. These lesions
demonstrated relatively homogeneous signal that were isointense to slightly hyperintense
on T1-weighted and markedly hyperintense on T2-weighted scans, relative to skeletal
muscle. The foci of the similar signal intensities were also demonstrated within the
subcutaneous tissues of left buttock and gluteus maximus muscle. However, here they
appeared nodular and had a feathered pattern ([Fig. 2]).
Fig. 2 Axial T1-weighted (A) and T2-weighted fat-saturated (B) magnetic resonance imagings of the right thigh. On serial axial images, the medial
subcutaneous thigh mass (arrow) was shown to be continuous with smaller foci of identical
signal in the posterior and lateral thigh. These demonstrated relatively homogeneous
signal that was isointense to slightly hyperintense on T1-weighted (A) and markedly hyperintense on T2-weighted scans, relative to skeletal muscle.
The patient was recalled for wide field of view images of the entire pelvis, including
axial T2-weighted fat-saturated and coronal short-tau inversion recovery. This confirmed
the findings of the prior MRIs. Moreover, these abnormal signal foci were bilateral
and largely symmetrical. Again, the subcutaneous nodular pattern and intramuscular
feathered pattern were noted. These features were consistent with a diagnosis of migration
of the HA gel agent from the buttock onto the medial aspect of right thigh ([Figs. 3] and [4]).
Fig. 3 Axial T1-weighted (A) and T2-weighted fat-saturated (B) magnetic resonance imagings of the right buttock. Foci of the same signal intensities
as demonstrated in Fig. 2 are demonstrated in the subcutaneous fat, where they have
a nodular pattern (arrow) and within the gluteus maximus muscle, where they have a
feathered pattern. Also, despite the patient being listed as female on the RIS, a
prostate gland is noted within the pelvis. RIS, Radiology information System.
Fig. 4 The patient was recalled for wide-field of view images of the entire pelvis, including
axial T2-weighted fat-saturated (B) and coronal short-tau inversion recovery (A and C). Again, the subcutaneous nodular pattern and intramuscular feathered pattern are
noted. On the left, the abnormal signal extends into the subcutaneous tissue of the
left scrotum, external to the inguinal canal (arrow). Despite the patient being listed
as female on the RIS, a penis and scrotum are noted.
In the absence of pain, the patient was managed with outpatient monitoring and observation.
Reassurance was given.
Discussion
HA is a naturally occurring polysaccharide found distributed within healthy connective
tissues across various parts of the body.[3] Its function is to stabilize the extracellular matrix by attracting water and creating
volume for extrastructural tissue support. Through this concept, HA gel injection
fillers (HAI) have been developed and approved for use in aesthetic medicine. HAI
preparations are most commonly used in facial aesthetic practice.[7]
[8] Common sites include the lips, chin, facial lines, nasolabial, and melolabial folds.
HAI of the buttocks is not as common, but gradually increasing in popularity, especially
with the increase in transgender transitions.[4]
The side effects of HAI are uncommon, and are often localized, comprising hematoma
formation, infection, localized erythema, or allergic reactions. Late complications
may include foreign body granulomas, chronic deep infections, and cross-link reactions
between different fillers (oedema, discoloration, nodules, ulcers).[5]
[6] HAI filler migration is a very rare complication, and according to the authors knowledge,
has rarely been described in the literature.[9]
[10]
[11]
[12]
[13] Moreover, HAI migration is often difficult to diagnose as reactions may occur months
after injection and lumps formed distant to the site of filler injections would not
routinely be considered a HAI filler complication. The phenomenon behind this migration
is not well understood; however, it is thought to occur due to its hydrophilic nature
and the diffusion permeability of the fibrous septae found between subcutaneous tissue
layers.[5]
[12] Given the rarity of this complication, imaging often plays a critical role in diagnosis.
Hence, it is necessary for radiologists to understand complications of HAI, progression
and be able to delineate imaging features to avoid misinterpretation of MRI and USS
as well as expedite therapeutic solutions in indistinct cases.
The imaging features of HAI can be somewhat misleading and nonspecific. Radiological
features can mimic a neoplasm. USS is usually the initial investigation for any superficial
lump and many studies have shown its efficacy in localizing commonly used fillers
as well as detect filler-related complications. US of HAI are usually hypoechoic;
however, in our case this was hyperechoic that could be due to leakage into the subcutaneous
tissues distant from initial site of injection. USS also plays a role in identifying
the differentials of other soft tissue lesions. However, USS imaging of filler-related
lumps is affected by the site and the time elapsed from injection, often complicating
the diagnosis.[14] MRI is thought to be the best imaging modality to classify HAI lesions and has the
advantage of accurately evaluating the volumetric and temporal changes of HA fillers.[15] HA filler lumps are best seen on fluid-sensitive fat saturated sequences. They possess
appearances similar to that of water, with a faint peripheral enhancement at the early
stages of injection and show progressive dissolution by 1 year on serial MRI.
Vascular malformation can be considered in the differential diagnosis of such lesions,
if there is no relevant history. However, the fact that this was bilateral symmetrical
and absence of increased signal on Doppler imaging are against this. These findings
are contrary to features of a sinister lesion.
The treatment of migrated HA filler lesions is usually dependent on symptoms. This
can involve aspiration or surgical drainage in symptomatic cases. To minimize the
risk of migration, certain theories have been described in the literature. These include
using low-pressure filler injections, limiting physical activity in the immediate
post-injection period, and having more than one treatment session.[12]
[16]
