ACNES: A Hidden Cause of Abdominal Pain
Gonzalez-Sandoval JF *1, Castañeda-Hernandez GJ 1, Aréchiga Ornelas GE 2,
Castañeda de la Lanza C 3
*Correspondence to: Gonzalez-Sandoval JF, Palliative Care and Pain Medicine Resident, Hospital General de Occidente, Zapopan, Jalisco, México.
© 2025: Gonzalez-Sandoval JF. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: 16 August 2026
Published: 01 September 2026
DOI: https://doi.org/10.5281/zenodo.22267664
Abstract
Introduction: Anterior cutaneous nerve entrapment syndrome (ACNES) is a cause of chronic abdominal wall pain resulting from entrapment of the anterior cutaneous branches of the thoracoabdominal nerves. Its diagnosis is clinical and is based on the presence of focal pain, local sensory abnormalities, a positive Carnett sign, and response to local anesthetic blockade.
Case presentation: A 41-year-old woman with a history of two cesarean sections, bilateral tubal occlusion, cholecystectomy, and appendectomy presented with localized pain in the anterior abdominal wall of eight months’ duration, with a maximum intensity of 10/10 on the verbal numerical analog scale (VNAS). Previous surgical and gynecological evaluations ruled out acute abdominal or gynecological pathology. Sensory mapping identified areas of hyperalgesia, hypoesthesia, and allodynia, as well as well-defined painful points, in addition to a positive Carnett sign. Based on these findings, the diagnosis of ACNES was established.
Intervention: An ultrasound-guided block from the transversus abdominis plane was performed, accompanied by hydrodissection of the neurofascial territory corresponding to the area of pain. Ropivacaine 0.2% (16 mg) and dexamethasone (8 mg) were administered, in a total volume of 10 mL, through a 22G Quincke needle under continuous ultrasound visualization.
Results: After the procedure, pain intensity decreased from 10/10 to 2/10 on the VNAS. Allodynia disappeared, the Carnett sign became negative, and repeat sensory mapping showed an approximately 90% reduction in painful areas. Clinical improvement was maintained throughout the 12-month follow-up period, without significant recurrence.
Conclusion: Ultrasound-guided targeted blockade in the transversus abdominis plane, associated with hydrodissection, produced a sustained reduction in pain and sensory abnormalities in this patient with ACNES. This technique may represent a minimally invasive alternative for selected patients, particularly those with a history of abdominal surgery.
Keywords: Anterior cutaneous nerve entrapment syndrome; ACNES; Abdominal wall pain; postsurgical pain; TAP block; hydrodissection; ultrasound; neuropathic pain.
Introduction
Chronic abdominal pain represents a diagnostic challenge due to the diversity of visceral, musculoskeletal, and neurological structures capable of causing it. Among the causes arising specifically from the abdominal wall is anterior cutaneous nerve entrapment syndrome (ACNES), a condition resulting from entrapment of the anterior cutaneous branches of the thoracoabdominal nerves as they course through the muscular and aponeurotic structures of the abdominal wall [1,2].
The anterior branches of the thoracoabdominal nerves traverse the abdominal wall before reaching the subcutaneous tissue and skin. At certain anatomical sites, particularly during their course through the fascial planes and the rectus abdominis sheath, they may be subjected to mechanisms of compression, traction, or entrapment. Anatomical changes secondary to surgery, fibrosis, and scarring may be factors in the onset or perpetuation of pain.
The clinical presentation is usually characterized by pain localized to a small and reproducible area of the abdominal wall, frequently associated with sensory abnormalities such as hyperesthesia, hypoesthesia, or allodynia. The Carnett sign is one of the main clinical signs used to differentiate a parietal origin of pain from a probable visceral origin, as pain intensity is maintained or increased during active contraction of the abdominal musculature [1,2].
In a series of 1,116 patients diagnosed with ACNES, Mol et al. reported a high frequency of a positive Carnett sign, sensory abnormalities in the painful territory, and a significant response to local anesthetic infiltration, characteristics that underscore the importance of an adequate physical examination in establishing the diagnosis [1].
The treatment of ACNES is usually approached through a stepwise strategy. Diagnostic and therapeutic infiltrations with local anesthetics are generally among the first interventions, while techniques such as pulsed radiofrequency or neurectomy are reserved for persistent or refractory cases [3,4,5,6]. However, the development of ultrasound-guided techniques has enabled nerve blocks and targeted interfascial approaches with greater anatomical precision.
The transversus abdominis plane block (TAP block), targeted to the symptomatic territory, has previously been described as a therapeutic alternative in ACNES. Nizamuddin et al. reported its use in pediatric patients [1], while Sahoo and Nair reported clinically significant relief following an ultrasound-guided TAP block in patients with this condition [2].
The combination of a targeted interfascial block with hydrodissection makes it possible not only to obtain the pharmacological effect of the local anesthetic, but also to achieve controlled separation of the fascial interfaces along the course of the nerve. Nevertheless, the available evidence regarding hydrodissection in ACNES remains limited.
We present the case of a patient with chronic abdominal wall pain and clinical features compatible with ACNES, in the context of multiple abdominal surgical procedures, treated with a targeted ultrasound-guided block in the transversus abdominis plane associated with hydrodissection, with marked reduction of the painful territory and sustained clinical benefit for 12 months.
Case report
A 41-year-old female patient presented to our clinic with chronic pain of approximately eight months’ duration, predominantly localized to the anterior abdominal wall, which began after the most recent abdominal surgical intervention.
Her surgical history included multiple abdominal and gynecologic-obstetric procedures: two cesarean sections, bilateral tubal occlusion, cholecystectomy, and appendectomy. She had abdominal scars, including a midline infraumbilical scar, as well as McBurney and Kocher scars.
The patient described sustained pain of 10/10 ENVA intensity that did not decrease, located mainly in relation to the areas of surgical scarring and accompanied by tactile allodynia. The clinical picture showed predominantly somatic characteristics of abdominal wall pain, accompanied by a visceral, dull, poorly localized, deep sensation.
Due to the condition's characteristics and persistence, she had previously been evaluated by the surgery and gynecology departments. Following the corresponding evaluations, no acute surgical abdominal pathology or acute gynecological disease was identified that could account for the intensity, persistence, and distribution of the pain. A targeted examination of the abdominal wall was performed using systematic sensory mapping. A heterogeneous distribution was documented, characterized by alternating areas of hyperalgesia and hypoesthesia, with marked allodynia within the painful territory.
Multiple clearly defined and reproducible tender points were identified on palpation. When the Carnett maneuver was performed over the point of maximum tenderness, the pain persisted or increased during contraction of the abdominal musculature, which is considered a positive Carnett sign. (Figure 1.)
The association of localized abdominal wall pain with both positive and negative sensory abnormalities, allodynia, and a positive Carnett sign, together with the absence of an acute abdominal or gynecological cause to explain the symptoms, supported the clinical diagnosis of anterior cutaneous nerve entrapment syndrome (ACNES) [1,2,3].
Given the history of multiple surgical interventions and the distribution of pain around the abdominal scars, the presence of postoperative fibrotic and adhesive changes was additionally considered as a possible contributing factor to nerve entrapment and pain perpetuation.
Intervention
Using a linear ultrasound transducer, the internal and external oblique abdominal muscles, rectus abdominis, and transversus abdominis were identified. The approach was directed toward the lateral region of the right rectus abdominis sheath and its continuity with the neurofascial planes of the abdominal wall, aiming to reach the territory corresponding to the course of the involved cutaneous nerves.
Under aseptic technique and continuous ultrasound visualization, a 22G Quincke needle was advanced using an in-plane approach, maintaining visualization of the needle tip throughout the procedure.
Once the target plane was reached and after negative aspiration, a solution consisting of ropivacaine 0.2% (16 mg) and dexamethasone (8 mg), with a total volume of 10 mL, was progressively administered.
The progressive administration of the solution allowed ultrasound visualization of separation of the fasciae of the internal oblique and transversus abdominis muscles, lateral to the rectus abdominis muscle, and its distribution along the selected neurofascial territory. In this manner, the procedure combined a targeted transversus abdominis plane block with ultrasound-guided hydrodissection of the territory corresponding to the probable nerve entrapment.
Clinical course and follow-up
At the post-intervention assessment, the patient reported a marked decrease in overall pain intensity, recorded as 2/10 ENVA, compared with previous values of up to 10/10.
This corresponded to an initial approximate 80% reduction in pain intensity.
Systematic sensory mapping of the abdominal wall was subsequently repeated, using the territories previously identified before the intervention as a reference. This reassessment showed an approximate 90% reduction in the previously mapped painful areas.
Likewise, disappearance of the allodynia that had been clearly identified before the procedure was documented.
The Carnett maneuver was repeated in the previously painful territories and was negative, in contrast to the clearly positive finding documented before the intervention.
These changes made it possible to objectively demonstrate not only a decrease in overall pain intensity but also a significant change in the anatomical distribution of sensory abnormalities in the abdominal wall.
The therapeutic response was maintained over a 12-month follow-up period, without clinically significant recurrence of the initial condition and with preservation of the improvement achieved after the procedure.
Discussion
The present case includes multiple clinical characteristics described in the diagnosis of ACNES: chronic, focal abdominal wall pain; reproducible tender points; local sensory abnormalities; allodynia; and a positive Carnett sign. Additionally, the patient had previously been evaluated by the surgery and gynecology services, without identification of an acute visceral etiology to explain the condition.
These findings are consistent with those described by Mol et al. in a cohort of 1,116 patients diagnosed with ACNES, in which the Carnett sign, abnormalities of cutaneous sensation, and the presence of a localized tender point were central elements for the clinical recognition of the syndrome [1].
Sensory mapping of the abdominal wall was a particularly relevant element in this case. Before the procedure, positive sensory phenomena, such as allodynia and hyperalgesia, were documented and coexisted with negative phenomena represented by areas of hypoesthesia. This distribution supported the presence of peripheral nerve dysfunction and enabled anatomical definition of the territory suitable for intervention.
The usefulness of the mapping was not limited to the initial assessment. Its repetition after the procedure enabled objective demonstration of an approximate 90% reduction in the previously identified painful areas, providing an additional clinical parameter alongside the conventional measurement of pain intensity.
This modification of the painful territory was accompanied by disappearance of allodynia and a decrease in the overall ENVA score. The conversion of an initially positive Carnett sign to a negative sign after an intervention targeting the abdominal wall is a particularly interesting finding, as it suggests a clinically relevant modification of the parietal pain generator.
The patient had a history of five abdominal surgical procedures, including two cesarean sections, bilateral tubal occlusion, cholecystectomy, and appendectomy. Although a causal relationship between these procedures and nerve entrapment cannot be established from a single case, it is anatomically plausible that scarring, fibrosis, and modification of the fascial planes may contribute.
The localization of pain around the infraumbilical and suprapubic scars was particularly relevant. However, the diagnosis of ACNES must be conceptually differentiated from that of an intra-abdominal adhesion syndrome. Whereas the latter mainly refers to peritoneal or visceral adhesions, the presence of allodynia, hypoesthesia, hyperalgesia, and a positive Carnett sign in our patient pointed toward a predominantly parietal and neuropathic component.
The marked response following an intervention directed at the neurofascial territory provides additional support for this interpretation. Pain initially decreased from 10/10 to 2/10, with the painful territory reduced by approximately 90%, allodynia resolved, and the Carnett sign became negative.
Diagnostic and therapeutic blocks are part of the management of ACNES. Boelens et al. studied 139 patients using a stepwise strategy that included local infiltrations and, in refractory cases, anterior neurectomy. A substantial proportion experienced a significant reduction in pain following infiltration treatment, while neurectomy showed favorable results in selected patients [9].
The possibility of using a TAP block specifically targeted to the painful territory has previously been described. Nizamuddin et al. reported the use of targeted TAP blocks in three pediatric patients with ACNES [7]. Subsequently, Sahoo and Nair described two cases treated with ultrasound-guided TAP block, with significant and prolonged pain relief [8].
These experiences support the concept that the TAP block may be used not only as a broad regional block of the abdominal wall, but also as a targeted procedure when there is adequate correlation between the site of maximum tenderness and the anatomical course of the thoracoabdominal nerves.
The review by Top et al. identified various interventional strategies used in ACNES and documented favorable outcomes with TAP blocks across different series, although it highlighted heterogeneity in techniques, study populations, and definitions of therapeutic success [9].
Potential role of hydrodissection
A distinctive aspect of the present case was the use of ultrasound-guided hydrodissection associated with the transversus abdominis plane block.
The progressive administration of 10 mL of solution made it possible to visualize in real time the separation of the fascial interfaces and its distribution along the selected neurofascial territory. The solution consisted of ropivacaine 0.2%, at a total dose of 16 mg, associated with dexamethasone 8 mg.
From a pathophysiological standpoint, several mechanisms may explain the observed response. First, the effect of the local anesthetic on peripheral nociceptive conduction. Second, the distribution of the solution along a broader segment of the nerve course. Finally, hydraulic separation of the fascial interfaces could temporarily modify the compressive or traction forces exerted on the affected neural structures.
However, these mechanisms should be interpreted with caution. The present case does not allow demonstration that the improvement was exclusively the result of mechanical release of the nerve, since local anesthetic and dexamethasone were administered simultaneously. For this reason, it is scientifically more accurate to describe the procedure as a targeted TAP block associated with ultrasound-guided hydrodissection, avoiding attribution of the benefit to a single mechanism.
The persistence of the result throughout 12 months of follow-up represents one of the most relevant findings of the case. The duration of the benefit far exceeds the expected pharmacological effect of the local anesthetic, raising the possibility that additional mechanisms, such as modification of the neurofascial environment or prolonged interruption of peripheral sensitization, may have contributed. However, the observational nature of a case report precludes the establishment of causality.
In refractory patients, alternatives such as pulsed radiofrequency and anterior neurectomy have been described. Maatman et al. compared both strategies in a randomized clinical trial and demonstrated that neurectomy was more effective for certain outcomes, although pulsed radiofrequency may represent a minimally invasive alternative within a stepwise approach [4].
Subsequent reviews continue to show considerable heterogeneity among the therapeutic strategies available for ACNES and support individualized treatment [4,6]. In this context, a targeted TAP block associated with hydrodissection could represent an alternative prior to neuroablative or surgical procedures in selected patients.
Another potentially relevant aspect of the present case is the use of sensory mapping as a tool to assess response. Outcomes of pain interventions are usually expressed primarily as changes on numerical scales. In this patient, systematic repetition of the map made it possible to document an approximate 90% reduction in the painful territory, the disappearance of allodynia, and a negative Carnett sign, providing complementary clinical information regarding the therapeutic response.
Limitations
The present study shares the inherent limitations of a single case report. The observed response cannot be extrapolated to the entire population with ACNES, nor does it allow superiority over other therapeutic strategies to be established.
Likewise, the procedure combined ropivacaine, dexamethasone, and hydrodissection, making it impossible to independently determine the contribution of each component to the clinical outcome.
The coexistence of multiple previous abdominal surgical procedures and scar-related changes represents another factor that makes it difficult to attribute the entirety of the symptoms to a single pathophysiological mechanism.
The approximate 90% reduction in the painful territory was determined by clinical remapping and, although it provides a useful parameter for comparing the pre- and post-treatment states, it does not correspond to a quantitative tool specifically validated for ACNES.
Nevertheless, the concordance among multiple clinical outcomes—decreased pain intensity, reduced extent of the symptomatic territory, disappearance of allodynia, conversion of the Carnett sign to negative, and maintenance of the benefit for 12 months—reinforces the relevance of the observed response.
Conclusion
Anterior cutaneous nerve entrapment syndrome should be considered in the differential diagnosis of patients with localized chronic abdominal pain, particularly when cutaneous sensory abnormalities, well-defined tender points, and a positive Carnett sign are observed.
In the presented case, a targeted TAP block associated with ultrasound-guided hydrodissection using ropivacaine 0.2% and dexamethasone produced a marked reduction in pain intensity.
Post-intervention remapping demonstrated an approximate 90% reduction in the painful territory, accompanied by the disappearance of allodynia and a negative Carnett sign.
The therapeutic response remained stable over 12 months of follow-up, which represents a finding of particular interest given the minimally invasive nature of the procedure.
The combination of systematic sensory mapping of the abdominal wall with ultrasound identification of the neurofascial planes may enable an individualized approach to both selecting the territory for intervention and objectively assessing the clinical response.
Targeted TAP block associated with ultrasound-guided hydrodissection represents a potentially useful strategy in selected patients with ACNES. Prospective and comparative studies are needed to determine its efficacy, duration of benefit, optimal solutions and volumes, and its eventual position within established therapeutic algorithms.
References