Chronic expanding haematoma in a cat

Abstract

A 5-year-old cat developed a recurrent haematoma in the right hindlimb after receiving an intramuscular injection. Cold packs and a compressive bandage were applied without success. The haematoma resolved initially but recurred twice within a week after conservative treatment. Contrast computed tomography was performed after the second recurrence. A large cavernous lesion was found craniolateral to the right stifle. The lesion was removed surgically. No recurrence occurred during a 5 month follow-up. On histopathology the lesion was characterised as a chronic expansive haematoma. To our knowledge, this type of lesion has not previously been described in a small animal.

Case Report

In humans, tangential shearing injuries can cause a separation of the skin and the subcutaneous fat from the underlying fascia, forming a dead space that may be filled with blood, lymph, serum or a mixture of these fluids. The accumulation of fluid is usually surrounded by a fibrous pseudocapsule.^1–5 This lesion is commonly designated a ‘Morel–Lavallée lesion’, but other terms are also used, such as ‘closed internal degloving injury’, ‘post-traumatic soft tissue cyst’, ‘chronic expanding haematoma’ and ‘Morel–Lavallée extravasation or effusion’. ¹ In this report, we describe a case of a chronic expanding haematoma in a cat and postulate a pathogenesis.

A 5-year-old male castrated domestic shorthair cat was sedated for routine radiography 6 weeks after surgical repair of an ilial fracture. The cat was not lame at the time of the investigation. An intramuscular injection of medetomidine (10 mg/kg), ketamine (6 mg/kg) and midazolam (0.3 mg/kg) was given in the proximal part of the right hindlimb using a syringe and a 22 G hypodermic needle. During the injection the cat became very agitated while the needle was still in the muscles of the hindlimb. Within minutes after the injection a swelling developed. There was no discolouration of the skin. Cold packs were applied and tranexamic acid was administered intravenously at a dose of 15 mg/kg body weight to prevent further blood loss. Results of blood chemistry, complete blood count, prothrombin time (PT), activated partial thromboplastin time (aPTT) and rotational thromboelastometry (ROTEM Delta) were within normal limits.

The patient was hospitalised overnight. The next day the swelling had markedly decreased and vital parameters were within normal limits. The cat was discharged without medication. The owners were advised to restrict the cat’s movement for 3 weeks.

Seven days later the swelling had recurred. It was half a tennis ball in size and extended distal to the stifle. On palpation, there was slight fluctuation.

Aseptic aspiration of the swelling yielded 50 ml of aspirate with a haematocrit (Ht) of 31%; the Ht of a simultaneously taken blood sample was 38% (reference interval [RI] 33–45%). Following aspiration, a compression bandage was applied. Cefovecin was administered at a dose of 8 mg/kg body weight to prevent infection. The bandage was removed the following day. The leg had returned to its normal size and the cat was discharged without a bandage. Restriction of movement was recommended as before.

Eight days later, the cat was again presented with a fluctuating mass in the same leg. As at previous presentations, the skin looked healthy. The size of the swelling did not change over the next 4 days. The cat’s gait was normal and the leg was not painful on manipulation.

Aspiration of the swelling yielded 60 ml of haemorrhagic fluid with a Ht of 31% and a protein content of 56 g/l. A simultaneously taken peripheral blood sample had a Ht of 34% and a protein content of 70 g/l (RI 64–80 g/l). Thrombocyte count, PT, aPTT, ROTEM Delta and mucosal bleeding time using a lancet (Surgicutt adult; ITC) were within their RIs. The cytological diagnosis of the aspirated fluid was pure blood without evidence of neoplastic cells.

Computed tomography (CT) of the thorax, abdomen and both hindlimbs was performed using a 16 slice helical scanner (Phillips Brilliance CT 16 slice; Phillips). Angiographic CT of the pelvis and hindlimbs was performed immediately after pre-contrast. An iodinated contrast medium (Acupaque 350, Iohexol; GE Healthcare) was administered intravenously at an injection rate of 1 ml/s (Accutrom CT-D, Medtron, Firma SMD; Medical Trait). Acquired images were reconstructed and exported to a workstation (OsiriX v 4.1. 64-bit, DICOM Viewer; www.osirix-viewer.com).

A large cavernous lesion extended craniolateral to the right stifle between the subcutaneous fascia, the quadriceps muscle, the patella and the planum cutaneum of the tibia. There was mild contrast enhancement of the capsule. No vessels were identified in close proximity to the lesion and there was no indication of an underlying disease (Figure 1a,b). The radiographic diagnosis was a fluid-filled occupying mass.

Figure 1

(a) Computed tomography (CT) reconstruction of a transverse section of the hindlimbs at the level of the stifle in the venous phase after intravenous (IV) contrast administration. Right leg: a round subfascial space-occupying lesion is seen cranial to the moderately compressed biceps femoris muscle extending towards the patella. This lesion shows a central region of hypoattenuation in comparison with the musculature with thin rim enhancement. (b) Dorsal CT reconstruction of the upper hindlimbs in venous phase after IV administration of contrast medium. The lesion is extending to the mid-diaphyseal level of the right femur, compressing the right biceps femoris muscle. F = femur; GC = ossa sesamoidea with adjacent musculus gastrocnemii; BF = biceps femoris; H = haematoma/lesion

The decision was made to remove the haematoma and the capsule in their entirety. At surgery, the haematoma was well encapsulated (Figure 2). Active bleeding was not observed and an associated mass could not be identified. Adherence of major vascular structures to the capsule was not seen. Most of the capsule could be removed. The wound was closed, and attention was paid to eliminating dead space using monofilament suture material. A bandage was applied during the first night after surgery to provide mild compression. Non-steroidal anti-inflammatory drugs were avoided because of their possible effect on coagulation. Moderate lameness of the right hindlimb was noted after surgery. The lameness resolved in 10 days. The duration of hospitalisation was 5 weeks, partly owing to the owners’ vacation. Ht, PT and aPTT were performed prior to discharge. The Ht had returned to 42% after an initial fall to 20% before surgery. The remaining variables were within their RIs.

Figure 2

Intraoperative picture of the haematoma capsule (arrow)

Five months after discharge the owners confirmed the overall good condition of the cat and the absence of any swelling or lameness.

The term ‘chronic expanding haematoma’ is used if haemolymphatic fluid accumulates between the fascial planes, which was confirmed via CT scan. ¹ In humans, this condition is also called a Morel–Lavallée lesion. These lesions typically occur when tangential shearing injuries cause a separation of the skin and subcutaneous fat from the underlying fascia. These lesions typically arise at locations where superficial tissues can move easily relative to deeper structures. ⁶ A common site in humans is the area between the pelvis and the knee, ¹ as in our case. Extensive injury is common but not a prerequisite as Morel–Lavallée lesions have also been reported after minor trauma.^5,7 In our case, the hypodermic needle may have caused vascular trauma to the skin and subcutaneous tissue, potentially including a separation of the fascial planes. It is unlikely that a single injury caused by a needle will result in a chronic haematoma. In man the main cutaneous blood supply is provided by the perforator arteries, which run perpendicular to the skin. In the cat the main direct cutaneous vessels run parallel to the skin. Perforator arteries are also described in the cat but they are less prominent than in humans.^8,9 This difference makes cats less susceptible than humans to Morel–Lavallée lesions after shearing injuries. Despite the different pathogenesis in humans and cats the treatment is the same in both species.

Morel–Lavallée lesions can be classified into six types (Mellado and Bencardino classification) ² based on their appearance on magnetic resonance imaging (MRI), but MRI was not performed in our case and the lesion can therefore not be classified.

Soft tissue sarcoma and bursitis are two alternative diagnoses that need to be excluded. ³ In humans, MRI is the method of choice to distinguish between Morel–Lavallée lesions and neoplasia or bursitis. ¹ Based on the CT study of our case we did not expect neoplastic disease. This was confirmed by the absence of neoplastic cells on histopathological examination.

A subcutaneous haematoma due to trauma or a bleeding disorder is another alternative diagnosis, but this would typically present with discolouration of the skin and resolve over time. Coagulopathy was excluded based on the results of the coagulation tests that were performed.

Our patient had lost a significant amount of blood in the haematoma resulting in a Ht of 20% shortly before surgery. This is rare in humans but has been described after surgery. ¹⁰ Haemorrhage has been attributed to inflammation, which is also believed to initiate the formation of a pseudocapsule around the lesion. ² The most common complications in humans are necrosis of the skin and infection. ² These were not observed in our case.

In humans, conservative therapy has a success rate of <50%. Conservative treatment also failed in our case and prompted us to remove the mass surgically. Other treatments that have been applied in humans with varying results are sclerodesis, resection of the haematoma, closure of dead space, drainage and synthetic glue.^1,11,12

Conclusions

We conclude that chronic expansive haematoma can occur in cats and recommend surgical removal of the mass if conservative treatments fail.