Surgical removal of a cecal enterolith in a Rock Hyrax (Procavia capensis)

Abstract

The rock hyrax (Procavia capensis) is a small herbivorous mammal, and reports on gastrointestinal disease in this species are limited. Here, we describe the case of a 3-year-old female with intermittent anorexia. Computed tomography revealed a high-attenuation structure in the cecum, which gradually increased in size over time, as confirmed by serial radiography. Exploratory laparotomy was performed, and a multilobulated enterolith primarily composed of magnesium ammonium phosphate was surgically removed. The animal recovered without complications, and all clinical signs resolved. This is the first detailed report of enterolithiasis in a rock hyrax, emphasizing the importance of considering this condition in the differential diagnosis of gastrointestinal symptoms and demonstrating that surgical removal is an effective treatment option.

The rock hyrax (Procavia capensis) is a small mammal belonging to the order Hyracoidea, which is distributed across southwestern and northeastern Africa and the southeastern Arabian Peninsula [13]. Although its external appearance resembles that of rodents, genetic analyses have revealed that it belongs to the superorder Afrotheria, which includes elephants, manatees, and aardvarks [23]. In the wild, it inhabits rocky areas and feeds on herbaceous plants, lichens, and succulents [13]. Information on gastrointestinal diseases in captive rock hyraxes is limited. Kruse et al. summarized the gross and histopathological findings in 137 rock hyraxes and reported that the most frequently observed gastrointestinal conditions included sepsis originating from the liver or gastrointestinal tract, hepatic or intestinal hemosiderosis, islet and interstitial fibrosis of the pancreas, and enteritis/colitis [15]. Furthermore, a list of nutrition-related pathological findings compiled by Deborah et al. included diabetes mellitus, hepatic or intestinal hemosiderosis, gastrointestinal inflammation, and gastrointestinal obstruction as gastrointestinal-associated findings [5]. Gastrointestinal obstruction was observed in 2.9% of individuals. Although enterolithiasis was noted as one of the causes, its specific prevalence has not been reported [5]. To the best of our knowledge, no case reports describing enterolithiasis in this species have previously been published. This manuscript presents a case of cecal enterolith surgically removed from a rock hyrax.

The case involved a 3-year and 8-month-old female rock hyrax that was kept indoors and fed ground squirrel pellets (ground squirrel Selection Maintenance, Easter Co., Ltd., Tatsuno, Japan), Timothy hay, vegetables, and fruits. The animal presented with intermittent anorexia and a sloshing sound in the abdomen during movement. Radiographic examination revealed a multilobulated radiopaque structure in the lower abdomen, and palpation revealed a firm structure in that region. A computed tomography (CT) scanner (Aquilon Preime, Canon Medical Systems Co., Ltd., Tokyo, Japan) was used without contrast medium or anesthesia, while the animal was restrained in a laundry net, revealing a high-attenuation structure, 30 mm in diameter, within the cecum (Fig. 1). No continuity was observed in the gastrointestinal wall. Additionally, a separate 4-mm high-attenuation structure was observed in the distal portion of the cecum. No clear signs of peritonitis were observed in the surrounding abdominal fat tissue. Based on these findings, the differential diagnosis included gastrointestinal foreign bodies that could be cecal enteroliths. Although surgical removal was considered, given the mild clinical signs and high complication rate following enterotomy in rabbits [10], which are small herbivores similar to hyraxes, and the potential risk of dehiscence associated with enterotomy of the thin-walled cecum, conservative management was chosen to monitor changes in the size of the structure and clinical signs over time.

Fig. 1.

Coronal CT image. A high-attenuation structure (arrowhead) is observed within the cecum (arrow). Bar=3 cm.

Radiographic re-evaluations in the lateral and ventrodorsal views were performed on days 57, 162, 343, and 525 using an X-ray imaging system (MRAD-A50S RADREX; Canon Medical Systems Co., Ltd., Tokyo, Japan). Although the location of the structure remained unchanged during this period, its size gradually increased. The maximum diameters measured on the lateral radiographs were 37, 42, 48, and 49 mm. Anorexia episodes occurred intermittently, with a frequency of two to three times per month in most months, whereas no episodes were observed in some months. Anorexia temporarily improved with oral medications, including 0.6 mg/kg metoclopramide (Vomitbuster tablets, Kyoritsu Co., Ltd., Tokyo, Japan), 6.6 mg/kg dimethicone (Gascon tablets, Kissei Pharmaceutical Co., Ltd., Matsumoto, Japan), and 66.6 mg/kg probiotics (Mito Max Super, Kyoritsu Seiyaku Co., Ltd.), but recurred repeatedly. During episodes of anorexia, the animal occasionally showed signs of colic, including a prone posture with an extended abdomen and reluctance to move. In addition, sloshing sounds from the abdomen were consistently heard during movement. Based on the persistent clinical signs and progressive enlargement of the radiopaque structure, a presumptive diagnosis of a gastrointestinal foreign body was made. On day 525, surgery was performed after discussion with the owner. An exploratory laparotomy was performed on day 556.

Anesthesia was induced via intramuscular injection of 50 µg/kg medetomidine (Dorbene; Kyoritsu Seiyaku Co., Ltd.), 5 mg/kg ketamine (Ketalar; Daiichi Sankyo Co., Ltd., Tokyo, Japan), and 20 µg/kg buprenorphine (Zalvin; Nissin Pharmaceutical Co., Ltd., Toyama, Japan), followed by maintenance with 1% isoflurane (Isosol; Vedco Inc., Saint Joseph, MO, USA) via mask inhalation using a mixture of oxygen (3 L/min). On laryngoscopy, the soft palate appeared long and covered the epiglottis anteriorly, making it difficult to visualize the larynx. Therefore, a bronchoscope (Bronchoscope Model 1, Tokibo Co., Ltd., Tokyo, Japan) was used as a guide to visualize the larynx and trachea for intubation with a tracheal tube with a 3.0-mm internal diameter. After intubation, a 24-G 1/2 intravenous catheter (Venula S SS-7, Top Co., Ltd., Tokyo, Japan) was placed in the radial vein, and lactated Ringer’s solution (FUSO, Fuso Pharmaceutical Industries Co., Ltd., Osaka, Japan) was administered at a rate of 10 mL/kg/hr. Intraoperatively, the inspired oxygen concentration was maintained at 50% by mixing oxygen with medical air, and the end-tidal isoflurane concentration was maintained between 0.7% and 0.8%. Spontaneous respiration was maintained at a respiratory rate of 9–13 breaths/min, end-tidal carbon dioxide ranging from 25 to 35 mmHg, and percutaneous oxygen saturation of 98–100%. The esophageal temperature ranged from 34.2°C to 35.6°C. The heart rate ranged from 95 to 115 beats/min, and the noninvasive mean arterial blood pressure, measured with a cuff on the hind limb, was maintained between 60 and 90 mmHg. No pain responses, such as increased heart rate or blood pressure, were observed during surgical manipulation. After surgery, 250 µg/kg atipamezole (Atipame, Kyoritsu Seiyaku Co., Ltd.) was administered intramuscularly. The animal recovered completely after 6 min.

The patient had a sensitive temperament, and no preoperative hospitalization was performed to reduce stress. Preoperative subcutaneous 10 mg/kg enrofloxacin (Baytril, Elanco Japan Co., Ltd., Tokyo, Japan) was administered. A standard midline laparotomy was performed [26]. No ascites, inflammation, or adhesions were observed. A solid structure was observed within the cecum (Fig. 2). A cecotomy was performed, and the removed structure was identified as an enterolith. The enterolith was irregular in shape and multilobulated, measuring 4.5 × 3.5 × 3.5 cm and weighing 48 g (Fig. 3). Its surface was dark brown to black with a rough texture characterized by multiple deep grooves and was firm in consistency. The cecal incision was closed using 5–0 absorbable sutures (Monodiox; Alfresa Pharma Co., Ltd., Osaka, Japan). The cecal wall was closed using a two-layer suturing method, with the first layer employing a Gambee suture pattern and the second using an inverted suture pattern of the serosa. The abdominal wall was closed using continuous 3–0 absorbable sutures. The subcutaneous tissue was closed with continuous 4–0 absorbable sutures, and the skin was closed with simple interrupted sutures using 3–0 nylon (Nesco Suture, Alfresa Pharma Co., Ltd.). The total operative time from skin incision to closure was 43 min. Postoperative subcutaneous 0.3 mg/kg dexamethasone (Decadron, Sando Pharma Co., Ltd., Tokyo, Japan) was administered. The animal was returned home after full recovery from anesthesia with no postoperative hospitalization.

Fig. 2.

Intraoperative view of the cecum. A small incision was made to extract the enterolith (arrow).

Fig. 3.

Extracted enteroliths. The surface appears dark brown to black, exhibited a rough texture with multiple pronounced grooves, and demonstrated firm consistency. Bar=3 cm.

On the day after surgery, oral administration of 10 mg/kg enrofloxacin, 0.25 mg/kg meloxicam (Nichi-Iko Pharmaceutical Co., Ltd., Toyama, Japan), 10 mg/kg tranexamic acid (Transamin, Daiichi Sankyo Co., Ltd.), and 0.5 mg/kg famotidine (Sawai Pharmaceutical Co., Ltd., Osaka, Japan) was provided. Food intake, water consumption, and general activity were observed on the day following surgery. The sutures were removed two weeks after surgery. Postoperatively, intermittent anorexia, signs of colic, and sloshing sounds from the abdomen completely resolved. Radiographs taken at recheck on day 694 showed no evidence of enterolith recurrence. No recurrence of clinical signs was observed after surgery, and follow-up was performed. The enteroliths were analyzed using infrared spectroscopy (IR) with the KBr pellet method, in which a finely ground sample was mixed with potassium bromide and pressed into a transparent pellet for spectral measurements [12]. The analysis revealed that the enteroliths were composed of more than 98% magnesium ammonium phosphate.

To date, no study has compared different anesthetic protocols for rock hyrax treatment. Several anesthetic protocols for rock hyraxes have been described using different methods. Naylor et al. [22] reported the use of medetomidine, ketamine, and isoflurane for diagnostic imaging. Gravett et al. [9] reported the use of xylazine, ketamine, and isoflurane for electroencephalographic recordings. Moresco et al. [18] reported the use of midazolam, alfaxalone, ketamine, and isoflurane for surgical removal of hydrometra. Manharth et al. [16] reported the use of isoflurane alone for castration. In the present case, considering the need for a balanced anesthetic protocol, the protocol described by Naylor et al. [22] was used as a reference. Medetomidine, ketamine, and isoflurane were administered in combination with buprenorphine as an analgesic. This case demonstrates that anesthesia can be maintained at a low isoflurane concentration without a pain response, suggesting that medetomidine, ketamine, and buprenorphine may have achieved sufficient anesthetic depth. Hyraxes have an elongated soft palate that obscures the arytenoid cartilage, making visualization of the glottis difficult [16]. In the present case, the glottis could not be visualized using a laryngoscope. However, successful endotracheal intubation was achieved under bronchoscopic guidance, indicating that bronchoscopy may be a useful tool for airway management in this species.

In dogs, it has been reported that a two-layer closure consisting of appositional and inverting patterns following small intestinal enterotomy results in luminal narrowing, whereas a single-layer appositional closure demonstrates a more favorable healing outcome [14]. In contrast, a histological comparison of enterotomy closure at the pelvic flexure of the ascending colon in horses reported that a two-layer closure composed of appositional and inverting patterns exhibited good tissue alignment and a favorable healing process and was more effective in preventing leakage of intestinal contents than a single-layer closure [27]. Additionally, in an experimental study on rabbits, which are small hindgut fermenters, such as hyraxes, 80% of the animals developed leakage of intestinal contents following single-layer closure of the cecum transection [1]. In the present report, considering the thin cecal wall, a two-layer closure using appositional and inverting patterns [27] was performed to prevent the leakage of intestinal contents. As no postoperative complications were observed, this technique is suggested to be safely applicable, at least in this case.

Hyraxes are hindgut fermenters [6]. Although direct descriptions of the macroscopic characteristics of the cecal contents in healthy rock hyraxes are limited, previous studies have demonstrated that the cecum functions as a major fermentation chamber that contains fermenting digesta under normal physiological conditions [7]. Therefore, the presence of a large, firm enterolith observed in the present case represents a deviation from normal cecal physiology rather than a normal variation. In the present case, the animal exhibited signs of intermittent anorexia and colic, including reluctance to move, which resembled the clinical presentation of equine enterolithiasis [25]. While other gastrointestinal or systemic diseases could not be completely excluded and supportive therapy and spontaneous improvement may have contributed, in part, to the favorable clinical outcome, the complete resolution of the clinical signs after surgical removal of the enterolith, with no recurrence thereafter, suggests that the enterolith was the primary cause of intermittent gastrointestinal irritation.

As horses are the domestic species in which enterolithiasis has been most extensively studied, the following description summarizes equine enterolithiasis as a reference: enteroliths commonly form in the right dorsal colon [11, 25]. They may be asymptomatic or cause recurrent mild colic episodes [25]. Migration of an enterolith into the narrow descending colon can lead to gastrointestinal obstruction and severe acute colic [11]. Although the exact etiology of enterolith formation is unclear, factors such as reduced exercise due to stall confinement and a diet high in magnesium and phosphorus have been suggested as contributing factors [21, 24]. The most common component of enteroliths is magnesium ammonium phosphate, which forms through mineral accretion around a nidus, such as a small stone [8]. Although they are mostly spherical or tetrahedral, irregular morphologies have been observed [21, 24]. Diagnosis is made by radiographic examination, although they may also be discovered during exploratory laparotomy for colic [11, 25]. Surgical resection is the primary treatment for this condition [25]. Enteroliths have also been documented in herbivorous zoo mammals other than horses. For example, cases have been documented in Grant’s zebras in which both the clinical signs and stone composition were similar to those observed in equine enterolithiasis [17]. Enteroliths have also been described in tapirs, although mineralogical analyses have demonstrated that their composition differs from that of equine enteroliths, with vivianite and newberyite reported as the major components, rather than magnesium ammonium phosphate [20]. Considering the equine data, it is possible that the development of enteroliths in the hyrax in the present case was influenced by factors such as limited exercise due to indoor housing and the mineral content of the diet [21, 24]. However, there are several differences between horses and rock hyraxes. With regard to feeding behavior, horses are grazers that primarily consume grasses [2], whereas rock hyraxes are browsers that primarily consume shoots, buds, and leaves, with grass accounting for only a minor proportion of their diet [5]. In terms of gastrointestinal anatomy, rock hyraxes possess a connected colon linking the cecum and colonic sacs [7], whereas horses lack connected colons and colonic sacs [3]. Therefore, the etiological factors identified in horses cannot be directly extrapolated to this species, and the findings of this case report should be interpreted with caution, as they are based on a single case. Nevertheless, based on the clinical course and mineral composition of the enterolith, we consider that factors such as limited exercise and dietary mineral balance likely contributed to enterolith formation in this case.

Although the IR with the KBr pellet method employed in the present case is reliable for identifying major mineral components, several factors, including particle aggregation, moisture uptake, variability in sample mixing, particle size-related effects, and weighing inaccuracies, may limit the reliability of the quantitative interpretation [19]. Therefore, although the present analysis supports magnesium ammonium phosphate as the predominant component, complementary techniques, such as X-ray diffraction [4], would be valuable for a more definitive characterization of the relative composition. However, such analyses were not performed in the present study because of limitations in the analytical resources. Further studies incorporating additional analytical techniques would be valuable for confirming the detailed mineralogical composition.

To our knowledge, this is the first report of enterolithiasis treatment in a rock hyrax. Our findings suggest that enteroliths should be considered in the differential diagnosis of gastrointestinal symptoms in this species. Similar to horses, enteroliths may cause intermittent colic, and surgical removal appears to be an effective treatment. However, as this report describes only a single case, individual-specific factors, such as husbandry conditions, diet, and genetic background, may have influenced the clinical presentation. Further studies are needed to clarify the incidence, etiology, and appropriate treatment of enterolithiasis in rock hyraxes.

CONFLICT OF INTEREST

The authors declare no conflicts of interest directly related to the content of this article.