Acute non-traumatic abdominal pseudoherniation in a geriatric cat

Abstract

Case summary

A 16-year-old female spayed domestic shorthair cat presented with an acute mass-like outpouching of abdominal viscera unilaterally in the right caudal abdominal ventrum without history of trauma. This abnormality was not identified on prior diagnostic investigations for hyporexia up to 3 weeks prior. A CT examination revealed a protrusion of the viscus through an area of anomalous abdominal wall thinning associated with the discontinuation of the transverse abdominis muscle in this region, rather than a true hernia. Exploratory celiotomy confirmed these findings, with the external rectus sheath and parietal peritoneum remaining intact without an overt hernia ring identified. Abdominal wall augmentation and reconstruction using internal abdominal oblique advancement and fold-over external rectus sheath imbrication resulted in complete resolution without recurrence on subsequent follow-ups. Despite gastrointestinal and muscle biopsies showing no evidence of neoplasia on histopathology, the patient developed an abdominal effusion and was diagnosed with granular lymphocyte lymphoma 4 weeks postoperatively, leading to euthanasia.

Relevance and novel information

This case describes a non-traumatic abdominal wall pseudohernia in a geriatric cat, a condition which has not previously been reported. A novel reconstruction technique was used to correct the body wall anomaly, with a good short-term outcome without recurrence.

Introduction

Abdominal wall herniation is defined as the protrusion of internal organs through a defect in the supporting structure of the abdominal wall.^1,2 The most common reported causes in cats include trauma and congenital defects. ³ Abdominal wall weakness mimicking herniation attributed to acquired neurogenic atrophy of the supporting abdominal musculature has been reported in humans. ⁴ Although bladder herniation through an abdominal wall defect without a history of trauma has been previously described in a cat, ² there are no known reports of an acute non-traumatic abdominal pseudoherniation in a feline patient.

Case description

A 16-year-old female spayed domestic shorthair cat was referred for hyporexia and weight loss. The physical examination at this time was unremarkable, with no abdominal anomalies present. An abdominal ultrasound performed by a boarded small animal medicine specialist 3 days before referral revealed moderate focal thickening of the jejunal muscularis layer and mild generalised thickening of the ileal muscularis layer. Haematology and biochemistry, including total thyroxine, were unremarkable.

The repeat ultrasound performed upon tertiary referral was consistent with the initial findings. Serum cobalamin and folate levels were low (37 pmol/l, reference interval [RI] 214–1107; 19.8 nmol/l, RI 22.0–48.9, respectively). Feline pancreas-specific lipase returned within normal limits. Treatment consisting of maropitant, cobalamin supplementation and a hypoallergenic diet was initially trialled. One week later, the patient was started on prednisolone (5 mg q24h) because of ongoing hyporexia and diarrhoea.

The patient presented 1 week later for a notable mass-like protrusion from its abdomen. There was no history of trauma or recent abdominal surgery. Abdominal palpation revealed a palpable anomaly unilaterally in the right caudal abdomen, with underlying viscera protruding and laterally displacing the peritoneum proper. This outpouching was large, with no evidence of visceral entrapment or incarceration. No discomfort was appreciated on direct palpation. No external wounds, bruising, erythema or discharge were appreciated over the area of concern or remainder of the body. A small scar on the right caudal abdominal flank was identified, which was consistent with a previous flank spay performed at least 15 years earlier. Creatine kinase level was unremarkable.

General anaesthesia was undertaken via methadone (0.1 mg/kg IV) and midazolam (0.2 mg/kg IV) premedication, alfaxolone (2.1 mg/kg IV) induction and isoflurane maintenance. A CT examination of the thorax, abdomen and vertebral column with intravenous (IV) iohexol contrast administration demonstrated that the right caudal abdominal wall bulging was associated with the intestines and bladder. However, all contents remained within the peritoneum and not within the subcutaneous space. No subcutaneous emphysema was present. The transverse abdominis muscle in the right caudal abdomen appeared to be discontinuous in the affected region (Figure 1). No intrathoracic concerns, vertebral column anomalies, compressive or inflammatory radiculopathy, or myelopathy were appreciable.

Figure 1

CT images: (a) three-dimensional reconstruction demonstrating the anomalous ventral abdominal wall thinning of the right caudal abdomen (green arrowheads); (b) transverse plane CT image in soft tissue window demonstrating discontinuity of the transverse abdominis musculature (red arrowheads); and (c) dorsal plane CT image in soft tissue window demonstrating bulging of the right caudal abdominal wall (yellow arrowheads). Note there is no herniation of abdominal viscera into the subcutaneous space

The patient proceeded to exploratory celiotomy and abdominal wall reconstruction. Intraoperative analgesia was via fentanyl constant rate infusion (CRI) (6–21 µg/kg/h) and a ketamine CRI (0.6 mg/kg/h). Perioperative flucloxacillin (22 mg/kg IV q1.5h) was administered. A routine ventral midline approach from the xiphoid to the pubis was performed. The subcutaneous layer was dissected to evaluate the external rectus sheath and associated abdominal wall. These remained intact, with no overt herniation or full-thickness defect extending to the peritoneum appreciable. However, in the right caudal abdominal region, 2 cm caudolateral to the umbilicus, a palpable wall thinning was appreciable (Figure 2). After a routine ventral midline approach, no visceral adhesion to the ventral abdominal wall was appreciated. The prepubic tendon remained intact. The external and internal inguinal rings appeared appropriate bilaterally, without dilation or herniation of viscera within canal.

Figure 2

Surgical approach to exploratory celiotomy after elevation of the subcutis. This intraoperative image demonstrates obvious thinning and outpouching of the right caudal abdominal wall (yellow arrowheads)

Examination of the right caudal abdominal wall demonstrated significant thinning in a region approximately 4 × 3 cm in size, with an absence of the transverse abdominis (Figure 3). The external rectus sheath and parietal peritoneum remained intact, without an appreciable hernia ring defect. The external rectus sheath was carefully dissected superficially off the right rectus abdominis (Figure 4). No traumatic muscular defect was apparent, though the transverse abdominis remained absent in the right caudal abdomen.

Figure 3

Comparison of (a) the left lateral abdominal wall thickness with normal anatomy to (b) the right lateral abdominal wall with significant thinning. Note the rectus abdominus is present and normal bilaterally (green arrowheads). Where normal anatomy and presence of the transverse abdominus abaxially to the rectus abdominus are seen on the left lateral abdomen (blue arrowheads), there is a notable absence of this muscle, and thinning of the abdominal wall on the right lateral abdomen (yellow arrowheads)

Figure 4

Intraoperative photo after dissection of the external rectus sheath (blue arrowheads) over the area of the defect. This revealed only parietal peritoneum (green arrowheads) and demonstrates the notable lack of transverse abdominis muscle in the area of the defect. Rectus abdominis musculature is denoted (yellow arrowheads)

Further dissection abaxially allowed identification of the internal abdominal oblique muscle. Incisional muscle biopsies of the internal oblique and rectus abdominis were obtained for histopathology. The application of stay sutures allowed for axial advancement of the internal abdominal oblique (Figure 5a), which was then directly augmented onto the rectus abdominis using 2-0 polydioxanone (PDS; Ethicon) in a simple continuous suture pattern (Figure 5b). On palpation, resolution of the previous wall anomaly was identified; however, the right caudal abdominal wall still felt subjectively weak and thinner compared with the contralateral left side. The abaxial portion of the ipsilateral external rectus sheath was folded over axially on itself across the affected region and imbricated towards midline to create a ‘double-layered sheath’ via a vest-over-pants mattress suture using 2-0 polydioxanone. A marked improvement in abdominal wall thickness and integrity without further outpouching was then appreciable.

Figure 5

Intraoperative images: (a) identification of the internal abdominal oblique muscle (green arrowheads) with stay suture applied to allow axial advancement towards and overlying the rectus abdominis muscle (blue arrowheads); and (b) fold-over imbrication of external rectus sheath axially after direct augmentation of the internal abdominal oblique muscle onto the rectus abdominis muscle

Palpation across the gastrointestinal tract found no significant gross changes. The remainder of the abdominal exploration was unremarkable.

Given the previous ultrasonographic changes, routine full-thickness incisional biopsies were performed of the stomach, duodenum, jejunum and ileum. The linea alba was closed using 2-0 PDS in a simple continuous suture pattern. The subcutaneous layer was closed using 3-0 poliglecaprone 25 (Monocryl; Ethicon) in a continuous quilting pattern, ⁵ followed by intradermal skin closure using 4-0 Monocryl.

The patient’s recovery was uneventful and it was managed postoperatively with maropitant (1 mg/kg IV q24h) and fentanyl CRI (3.6 µg/kg/h). The patient was discharged 2 days later with buprenorphine (0.02 mg/kg sublingual q8–12h) and gabapentin (50 mg PO q8–12h) for 5 days. At the 2-week recheck, the abdominal wall reconstruction site remained comfortable, with no ongoing pseudoherniation appreciable.

On histopathology, the muscle biopsies returned as normal skeletal muscle without evidence of degenerative or denervation-associated atrophy. Gastric biopsies revealed mild lymphoplasmacytic gastritis. Intestinal biopsies revealed lymphoplasmacytic enteritis with moderate to marked lamina proprial infiltration of small lymphocytes and plasma cells consistent with inflammatory change. No overt neoplastic process was identified.

Four weeks after discharge, the patient re-presented for ongoing hyporexia. An abdominal ultrasound found a moderate amount of free fluid and loss of small intestinal wall layering. No recurrence of pseudoherniation continued to be identified. Cytology of the free abdominal fluid revealed a neoplastic effusion consistent with granular lymphocyte lymphoma. As a result of the associated grave prognosis, ⁶ the owners elected for euthanasia.

Discussion

Abdominal wall herniation, defined as the protrusion of visceral contents beyond the confines of the peritoneum, is well described in small animals.^{1 –3} These can be classified as true hernias, where they are enclosed within the peritoneum or hernial sac, such as umbilical, inguinal and femoral hernias, or false hernias, where they lack a peritoneal sac. Most traumatic hernias are false hernias. ³ Incisional hernias occur because of inherent tissue weakness after a previous incision.^2,3

The linea alba is the convergence of aponeuroses from the external abdominal oblique, internal abdominal oblique and transversus abdominis muscles.^1,7 The external abdominal oblique aponeurosis fibres run superficially over the rectus abdominis along the length of the abdomen. The internal abdominal oblique fibres pass both superficially and deep to the rectus abdominis in the cranial third, though only superficially caudal to the umbilicus. The transversus abdominis passes deep to the rectus abdominis cranially, though superficially in the caudal third of the abdomen.^1,8 In cats, the linea alba also progressively thins down from cranial to caudal. ⁷ A cadaveric experiment biomechanically evaluating the feline ventral abdominal wall determined that regions caudal to the umbilicus may be more prone to developing incisional herniation as a result of it being structurally weaker compared with cranially. ⁷

In the human literature, abdominal wall outpouching without herniation has been associated with acquired neurogenic atrophy of the supporting musculature, with multiple reported cases of underlying disease processes, including paralytic poliomyelitis, spinal meningioma, post-herpetic neuralgia and diabetic radiculitis. These cases usually show transient signs and self-resolve within months, with requirements for surgical fixation rarely reported. ⁴

The incidence of traumatic abdominal wall herniation and its associated surgical approaches are commonly described in cats.^1,3 In a case series of 10 cats and 26 dogs diagnosed with traumatic body wall herniation, 27% of the hernias in cats were of the ventral body wall, 27% were lateral paralumbar, 18% were due to cranial pubic ligament rupture and 9% were paracostal. Of the cats, 60% also suffered concurrent injuries, with a 20% mortality rate. ³ Surgical correction of acquired hernias often involves a midline approach to the linea alba, reduction of herniated contents and primary closure of the muscle defect with synthetic monofilament absorbable or non-absorbable suture material. Autologous techniques using local muscle flaps and use of bioprosthetics or synthetic mesh reconstruction can also be utilised in cases where primary closure is not possible.^{1,9 –13}

In this case, the patient had abdominal wall outpouching, consisting of an intact external rectus sheath and parietal peritoneum, without overt herniation. On investigation, the transverse abdominis muscle and aponeurosis were absent in this location. Surgical reconstruction via axial advancement of the internal abdominal oblique and novel imbrication of the external rectus sheath resulted in palpable and structural resolution of the abdominal wall outpouching. The patient recovered uneventfully from surgery and surgical repair remained intact on recheck 4 weeks later. Unfortunately, the subsequent diagnosis of lymphoma and euthanasia inhibits the reporting of long-term follow-up and remains a limitation to the efficacy of this repair. The use of an internal abdominal oblique muscle flap to correct a major abdominal wall defect has previously been described in a dog, with excellent long-term success. ¹¹

To the authors’ knowledge, there are no prior reports of non-traumatic abdominal pseudoherniation in cats. One case report similarly describes a caudoventral abdominal wall defect in a geriatric cat without history of trauma; ² however, that case was noted to have true herniation of the bladder through the defect and was concluded to be of idiopathic origin. Similarly, the significance of our case having undergone a prior flank spay procedure on the ipsilateral side of the abdominal wall anomaly remains unclear. Although poor apposition of the muscular layers during the initial procedure could be hypothesised, dehiscence or herniation would have been expected in the acute or subacute phase of recovery rather than occurring spontaneously 15 years later.

The relevance of the lymphoma diagnosis with the presentation of the abdominal pseudoherniation is uncertain. Although a single case study of renal lymphoma causing a peripheral neuropathy in a cat has been reported, ¹⁴ lymphoma-associated paraneoplastic acquired focal muscle atrophy of the abdominal musculature is deemed unlikely. Glucocorticoid-induced cachexia or age-related sarcopenia causing inherent weakness and pseudoherniation could be postulated as a cause, albeit the unilateral and focal presentation would be unusual. ¹⁵ Normal serum blood glucose levels rule out diabetic neuropathy, a known cause of abdominal pseudoherniation in humans. ⁴ Retroviral testing was not carried out in this patient, which is a limitation as feline immunodeficiency virus-associated myopathies have been reported in cats. ¹⁶ Furthermore, the patient’s vaccination status and prior exposure to feline herpesvirus were unknown. Although post-herpetic neuralgia is a recognised differential for pseudoherniation in humans, ⁴ it has not been reported in veterinary literature and could be considered.

Although myeloradiculopathy was not evident on CT, more definitive evaluation using MRI and electromyography would have been preferable and remains a limitation of this case study. ¹⁷

Conclusions

To the authors’ knowledge, this case report is the first to document a non-traumatic acute abdominal wall pseudoherniation in a geriatric cat. A novel reconstruction approach was described, demonstrating good short-term efficacy. Future studies with extended follow-up are necessary to properly evaluate the long-term efficacy of this technique.